Pump Maintenance

PAGE 1

1.0 INTRODUCTION

Pump is the machine that lifts liquids, moves them from place to place,

pressurises them for a number of useful tasks.

Enter into a power station. A number of pumps are in action - feeding water

to boiler, cooling the condenser, oiling the bearings etc. So it is obvious that

reliability, availability and efficiency of a power station depends a lot on the

behaviour of these machines; hence the importance of maintaining pumps in a well

planned way.

Implementation of the maintenance plan needs skilled and trained

maintenance personnel. ln the following section soft his book, attempt has been

made to acquaint trainees with different types of pumps used in power stations (See

Table 1. 1 Fig. 1. 1) and the ways of maintaining them systematically. A 'trouble

shooting chart' has also been added to enable the trainees to react quickly to

abnormal conditions.

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TABLE-I TYPICAL PUMP APPLICATION IN THERMAL POWER STATIONS

Sr. No.

Location/Name Type of Pump in Use Function of the Pump Remarks

1 Intake channel make up water pump

Vertical, Single Stage, Volute casing,Centrifugal

To maintain water level of the channel

2 Discharge Channel (C.T. Pump)

Vertical, Double Stage, Propeller type, Mix Flow

Pumping water through Cooling tower

When Cooling Towers are required to maintain water temperature

3 Control Structure H.P.5 Stages, Vertical. L.P. Pumps 3-stages, Vertical, Volute type

To supply water to various systems like fire fighting, E.S.P. for flushing, bottom ash removal,ash pump sealing and coolign system

4 Clarifloculator (Clarifired water pump)

Vertifical, Centrifugal To supply water to tretment plant for demineralising and for supplying clarifired water to plant equipment cooling

5 Intake channel inside Turbine House (Circulating water pump)

Vertical,Mix flow, two stage

To Provide cooling water to condenser

6 Hot well (Condensate Extraction Pump)

Vertical,Multistage, Centrifugal

To pump water from hot well through ejector to L.P. Heater to Dearator

For recycling the condensate to Boiler

7 O. Metre Turbine (Drip Pump)

Single-Stage, Centrifugal, Split casing, Horizontal

To maintain L.P. Heater level



PAGE 3



PAGE 4 8 O.Metre, B.F.P.

(Boiler Feed Pump) Multi stage, Barrel type Centrifugal

Feeding water to boiler drum through feed heters.

9 O.Metre, S.O.P. (Starting oil pump)

Vertical/Horizontal To Provide oil to bearings during start up.

Workings as taking oil pump.

10 O. Metre (Centrifuge Oil Purifier pump)

Vertical,Bowl type, centrifugal

To purify oil for recyling in the system

To Provide purified clean oil to turbine oil system for bearings and gover- ning systems.

11 O Metre Boiler Bay

i) Boiler Fill Pump i) Centrifugal, Multistage, Guidevanetype, or Single stage, Volute type

i) For filling the boiler for testing & startups.

ii) DM make up pump ii) Centrifugal,Single Stage, Volute type

ii) To provide make up water to the system

12 Ash pump House (-4 M level) (Slurry pump)

Closed impeller, Centrifugal, or Single stage Positive head

To remove slurry from ash channel to lagoons

13 13 Metre (Boiler) (Phosphate dosing pump.)

Reciprocating To inject trisodium phosphate to boiler drum water.

14 O. Metre, Turbine (Booster pump)

Single Stage, Radial Impeller

For bearing cooling of condenasate pump, boiler feed pump A.C. Lube oil pump, and to provide cooling water to Ball Mills.

PAGE 5

2.0 Classification of Pumps

Pumps are basically of three types

i Reciprocating

ii Rotary, and

iii Centrifugal

2.1 Reciprocating pump

In this type energy is added to the liquid by the to and fro movement of piston(s),

plunger(s), diaphragms etc.

Reciprocating pumps can be sub-divided into following varieties i) Piston pumps

i Plunger purnps



ii Ram pumps

iii Diaphragm pumps

2.2 Rotary pumps

Here the pumping action is caused by relative movement of rotating and

stationary elements of the pump. They can be sub-divided into following categories

i) Gear pump

ii) Screw pump

iii) Vane pump

iv) Lobe pump

2..3 Centrifugal pumps

This defination is applied to all types of pumps with an impeller housed in a

suitable shaped casing so that when the impeller rotates momentum is applied

toliquid in the pump casing transporting it from the inlet to the outlet side by

changing velocity into pressure energy. Centrifugal pumps are also sub-divided into

various categories which will be discussed in next chapter.

It can be seen from Table-1 that most of the pumps engaged in power stations

are of centrifugal type. So most of the discussions in the following chapters will

centre around centrifugal pumps.PAGE 6

3.0 Centrifugal pumps

Majority of the pumps used in Power Stations are of this category. It is the

machine that moves fluid by spinning it with a rotating impeller in a casing that has

a central inlet and a tangential outlet, as shown in Fig. 3.1 The path of the fluid is an

increasing spiral from the inlet at the centre to the outlet tangent to the annulus. The

(pressure) 'head develops against the inside wall of the annulus because the curved

wall forces the fluid to move in a circular path rather than by converting velocity

head to (pressure) head.

Useful work comes from the pump when some of the spinning fluid flows

from the casing tangential outlet into the pipe system. Power from the motor

accelerates the fluid coming in the inlet to the speed of the fluid in the annulus.

Some of the power is lost in fluid friction in the casing and impeller. Head

(pressure) is controlled by rpm, impeller diameter, and flow rate.



PAGE 7

3.1 Classification of centrifugal pumps

Centrifugal pumps are generally classified as under

Types Classification based on

Volute Casing (Fig. 3.2a)

Diffuser Casing (Fig. 3.2b)

Radial Flow lmpeller

Mixed Flow lmpeller Fig. 8.

Axial Flow lmpeller

Each of the above types can be further classified in many ways detailed below :

Single stage of multistage based on number of impellers mounted on the shaft.

Single suction or double suction depending on the number of liquid entrv Path

Axially split or radially split casing (See Fig. 3.20 Vertical/Horizontal pumps

3.2 Mulii Stage Pumps

If a larger head is required more impellers are to be fitted in series, so that the

discharge from the first impeller is guided into the inlet of the second impeller. This

is repeated with the third impeller and so on until the required head is reached. Each

impeller will increase the pressure by the same amount. A pump of this type is

called a multi stage pump A typical boiler feed pump may have as many as six to

eight stages.

All the impellers are keyed to the same shaft and usually all impellers dnd

diffusers of one pump are identical. This has the advantage of reducing the labour



in manufacture and stocking spares of maintenance. The discharge from each

diffuser is either circumferential or radial, this is collected by vanes attached to the

casing which direct, the liquid into the edge of the next impeller. The last diffuser

will discharge into the delivery pipe.

Fig. 3.3 shows 5 stage ring type pressure pump Fig.3.4shows a multistage vertical

pump used for condensate extraction.

PAGE 8

PAGE 9



PAGE 10

PAGE 11





PAGE 12

4.0 Rotary Pumps

4.1 Rotary pump is a positive displacement pump employing rotary motion.

This definition can be expanded further by saying that gear and vane pumps are of

the rotary type. Therefore, a gear-type pump is a rotary, positive displacement

pump. Most hydraulic systems use rotary pumps of the gear type.

The screw type rotary pumps is also a positive displacement pump but it is

constructed differently than the gear pump. It has the same general opera ting

characteristics. Usual] y, screw type pumps are used as itransfer pumps be cause of

their large capacities.

4.2 Gear Pumps

4.2.1 Gear pumps, sometimes called external gear pumps, are probably the most common

type of rotary pumps used for industrial applications. As previously mentioned,

hydraulic systems are the prime users of gear pumps. But many machine tools use

gear pumps for bearing lubrication as well as for supplying cu ' tting fluid to the

various points on the machine. In addition, the oil pump in the engines of most fork

lift trucks is.a gear type pump.

4.2.2 The operation of a gear pump, as shown in Fig. 4.1 is quite easy to understand. One

of the most common misunderstandings that people have about gear pumps

concerns the fluid flow. Many people first think that the material being pumped is

forced between the teeth of the gears and out the discharge side. As shown by the

arrows in the illustration, the material being pumped is drawn through the space

between the rotors and the Pump casing by the gear teeth and forced out of the

discharge port. The fluid is prevented from flowing back to the suction side of the

pump by the meshing of the gears.



PAGE 13

4.2.3 Although spur gear impellers are generally the most common type used in gear

pumps, both helical and herringbone gears are also used in many pumps. Two types

are shown in Fig. 4.2.,

4.3 Internal Gear Purnps

4.3.1 Another type of rotary gear pumps is the internal gear pump. This pump is entirely

different in construction than the standard or external gear pump.

4.3.2. The internal gear pump, as shown in Fig. 4.3 also consists of two gears in mesh with

one another. The outer or external gear of the set is the driving gear. The internal

gear is the driven or idler gear of the pump. T he: crescent keeps the gears separated

and reduces eddy currents, increasing the pump efficiency. In some models, it is

movable to allow the pump to operate in either direction.

4.3.3 In operation, the rotating internal gear opens the space between the teeth of both

gears at the intake port area. Fluid is drawn in through the

PAGE 14

intake port and passes around the crescent area of the pump. As the gear teeth again

come in contact with one another near the exit port, the fluid is discharged. Notice

that the driven gear has fewer teeth than the driving gear. However, the gears mate

smoothly at all times - without causing inter-ference. This occurs because the pitch

of gears is equal, even though the pitch diameter is unequal.



4.4 Vane Type Pumps

The vane type pump is another type of rotary pump used in many applications in

industrial plants. Although they are generally used for transferring hydraulic or

lubricating oil, they are also used for solvent or chemical transfer. Vane type pumps

are used for viscous materials such as paint or other heavy fluids which may contain

abrasive particles. For these applicaiions, the vanes are made of a softer material

than the pump casing. They wear less and are replaceable at a relatively low cost.

The, vane type pump shown in Fig. 4.4 is very simple in operation . As the impeller

rotates, its offset position above the pump centerline allows the vanes or blades to

extend and draw in fluid on one side. The open spaces between the impeller and the

housing at the bottom of the pump allow movement of the fluid through the pump.

As the impeller continues its rotation, the vanes are

PAGE 15

pushed back in their slot as they near the top of the pump. This constriction of

available space forces the fluid out of the discharge port.

The pump inlet and discharge ports are oval shaped and extend about three-

fourths across the casing width. This less than full opening helps con-tain the vane

within the pump casing. The oval shape smooths the fluid transfer.



4.5 Screw Pumps

4.5.1 Screw ' pumps are a special type of rotary positive displacement pump in which the

flow through the pumping elements is truly axial. The liquid is carried between

screw threads on one or more rotors and is displaced axially as the screws rotate and

mesh. In all other rotary, pumps the liquid is forced to travel circumferentially, thus

giving the screw pumps with its unique axial flow pattern and low internal velocities

a number of advantages in many application areas where liquid agitation or

churning is objectionable. Fig. 4.5(a)(b)

4.5.2 The applications of screw pumps cover a diversified range of markets such as navy,

marine, and utilities fuel-oil service, marine cargo, industrial

PAGE 16

oil, burners; lubricating-oil service; chemical process; petroleum and crudeoil

industries; power hydraulics for navy and machine tools; and many others. The

screw pump can handle liquids in a range of viscosity from molasses to gasoline, as

well as synthetic liquids in a pressure range of 3.5 to 350 kg/,tm2 and flows up to

1300 L/min.

4.5.3 Because of the relatively low inertia of their rotating parts, screw pumps a re

capable of operating at' higher speeds than other rotary or reciprocating pumps of

comparable displacement. Some turbine-attached lubricating-oil pumps operate at

10,000 rpm and even higher. Screw pumps, like other rotary positive displacement

pumps, are self-priming and hav@ a delivery flow characteristic which is essentially

independent of pressure.



PAGE 17

5.0 Reciprocating Pumps

5.1 A reciprocating pump may be defined as a pump that operates using a back and

forth, straight-line motion. Frequently the reciprocating pump is driven by an air or

steam-driven 'reciprocating piston. Some types of reciprocating pumps are driven

by a rotating crank shaft powered by an internal combustion engine or electric

motor.

5.1.1 Reciprocating pumps have two sections, the liquid section, and the steam.or air

section. The liquid section does the pumping. The steam or air section provides the

driving force necessary to operate the liquid section.

5.1.2 Although the pumping and driving ends may vary in construction in different

pumps, their general operating characteristics an esign are similar. The terms used

to describe the different components in the two sections (pumping and driving) are

similar in most cases, as shown in Fig. 5.l

PAGE 18

Piston - in the drive end converts the steam or air pressure into mechnical energy.

The piston in the pumping end converts the mechanical energy into fluid movement.

Piston Ring - acts as the seating element between the piston and the cylinder walls.

Cylinder - the tubular chamber that contains the piston.



Cylinder Head the cap on the end of the cylinder. The cap seals the cylinder and

allows'the piston to convert steam or air pressure into mechanical energy.

Packing Gland or stuffing box as it is also called, is located where the connecting

rod or piston rod passes through the cylinder head. The packing gland prevents

leakage of the steam or liquid from the cylinder.

Connecting Rod connects the piston on the pumping end to the drive section.

If the driving force is a crankshaft, the liquid-section connecting rod is usually

constructed in two pieces.

Valves - the valves are of two types. Either they control the power (steam or air)

flow into the driving side or the liquid flow into the pumping side. Although both

valves control flow, they are quite different in construction and operation. Note that

the valves in the di riving side of the pump are mechanically actuated, while the

valves in the pumping side are material actuated.

5.2 Diaphregrn Pumps

5.2.1 The pumping action of a diaphragm pump is similar to a single acting reciprocating

pump. This is shown in the diagram in Fig. 5.2., As the diaphragm is drawn into the

upper portion of the pump cavity, fluid is drawn into the pump through the check

valve in the suction line. As the diaphragm is driven downward, the fluid is forced

out of the cylinder through the check valve on the discharge side. As the cycle is

repeated, the discharge valve is closed by the pressure in the discharge side and the

suction created by the intake stroke.

5.2.2 Most diaphragm pumps are operated mechanically, but some are air- operated. Air

operated pumps can be operated by either compressed-air or Vacuum-air, depending

on the pump. Becaus @ of their simple construction

PAGE 19

these pumps are used for metering, transferring, or as sump pumps. Also,. they,can handle

fluids, scurries, or sewage.



5.2.3 The travel or stroke of the diaphragm in the mechanically operated pump is

controlled by an adjustable connecting r_od or other mechanism. The travel of air-

operated pumps is controlled by an adjustable diaphragm stop as shown in Fig. 4.2.

The stop limits the upward travel of the diaphragm rather than adjusting its overall

travel.

5.2.4 For handling chemicals or other corrosive fluids, pumps should be either lined or

manufactured of stainless steel or other corrosion resistant metals. If should be

remembered that the flow from a diaphragm pump is not steady, but pulsating.

PAGE 20

6.0 Construction of Centrifugal Pump



The Centrifugal pump in its simplest form consists of two main partse Stationary

parts consisting. of the casing, bearings and stuffing box. Rotating parts consisting

of the impeller and the shaft.

6.1 Casing

Casing or housing is the main casting which is firstly used to restrain the

water into an approximately circular or spiral path and secondly to collect the water,

as it is delivered from the periphery of the impeller.

It is provided with the inlet 'Suction', the outlet 'Discharge' and with a

stuffing box to permit the projection of the spindle or a shaft.

6.1.1 Materials for Casing

The following criteria should be considered in the selection of material for

centrifugal pump casings :

Strength

Corrosion resistance

Abrasive-wear resistance

Casting and machining properties

Cost

For most pumping applications cast iron is the preferred material for pump

casings when evaluated against initial cost. For single-stage pumps cast iron is

usually of sufficient strength for the pressures developed. For corrosive and volatile

products it may be necessary to specify cast steel or cast stainless steels.

Cast iron casings for multistage pumps are limited to approximately 10

kg/cm2 discharge pressure and 175"C. For temperatures above 17CC and pressures

upto 150 kg/tm discharge pressure, a cast steel is usually specified for split-casing

multi-stage pumps. For pressures higher than 150 kglcm2a cast or forged steel

barrel-type casing is required.

In any evaluation of cast iron versus steel casings, consideration should be given

to the probability of casing erosion during operation. Erosion can

PAGE 21

occur from either abrasive particles 'in- the fluid or from wire drawing across the

flange of c split-case pump. While the initial cost of a steel easing is higher than that

of a cast irom casing can often be salvaged by welding the eroded portions and then



remachining. Salvaging a cast iron casing by welding is not practical, and the

casing usually must be replaced.

The ductile irons are useful casing materials for pressure and temperature

ratings between cast iron and steels. While the modulus of elasticity for the ductile

irons is essentially the same as that for cast iron, the tensile strength is

approximately doubled. In any evaluation of the ductile irons as a substitute for the

steels in the intermediate pressure and temperature range, it must be remembered

that ductile iron casings cannot be effectively repair-welded in the field.

6.2 lmpeller

The, lmpeller can be described as a wheel having equally spaced Blades or

Vanes, arranged around the shaft.

At one side is the inlet or eye. From,the eye, the blades run in a curved path

to the outer edge of the wheel. (Fig. 6. 1)

6.2.1 Classification

lmpeller can be classified in various types as detailed below:

IMPELLERS

TYPE OF SUCTION FORM OF VANES MECHANICAL DESIGN

Single Double Radial Mixed Axial Over- Open Semi Closed

Suction Suction Flow Flow Flow h,u,ng Open

(See Fig. 6.2)



PAGE 22

PAGE 23

6.2.2 Materials for lmpelier

The following criteria should be considered in the selection of the material

for the impeller :


Abrasive-wear resistance

Cavitation resistance

Casting and machining properties



Cost

For most water and other noncorrosive services bronze satisfies these criteria

on an evaluated basis. As a result bronze is the most widely used im. peller material

for these services. 13ronze illipellers, however, should not be used for Pumping

temperatures in excess of 120'C. This is a limitation imposed primarily because the

differential rate of expansion between bronze and steel will produce an unacceptable

clearance between the impeller and shaft. The result would be a loose impeller on

the shaft.

Cast iron impellers are used to a limited extent in small low-cost pumps. As

cast iron is inferior to bronze in corrosion, erosion and cavitation resistance low

initial cost.wouid be the only justification for a cast iron impetier on an evaluated

basis.

Stainless steel impellers are widely used where bronze would not satisfy the

requirements for corrosion, erosion, or cavitation resistance. The stainless steels are

not used for seawater, however, as pitting will limit their performance life. The

stainless steels should be used where the pumping temperature exceed 120 0 C as

the differential expansion problem no longer exists with a steel impeller on a steel

shaft.

The austenitic stainless steels are the next step up on the corrosion and

cavitation-resistance scale. Initial cost is a factor here that should be evaluated

against the increased performance life.

6.3 The Shaft

The basic function of the shaft is to transmit the torque and supporting the

impeller and other rotating parts. The impeller is keyed to the shaft which is

supported at either ends by bearings. (Ref. Fig. 6.3)



PAGE 24

PAGE 25

The following criteria should be considered in the selection of the material

for a centrifugal pump shaft :

Endurance limit


Notch sensitivity

The endurance 1'tm'tt 'is the stress below which the shaft will withstand an

infinite number of stress reversals without failure. Since one stress reversal occurs

for each revolution of the shaft this means that, ideally at least, the shaft will never

fail if the actual maximum bending stress in the shaft is less than the endurance limit

of the shaft materials.



In actual practice, however, the endurance limit is substantially reduced

because of corrosion and stress raisers such as threads, keyways and shoulders on

the shaft. In the evaluation of the selection of the shaft mateiral consideration

must be given to the corrosion resistance of the material in the fluid being pumped

as well as the notch sensitivity.

6.3.1 Shaft Sleeves

Pump shafts are usually protected from erosion, corrosion, and wear at

stuffing boxes, leakage joints, internal bearings, and in the water ways by renewable

sleeves.

The most common shaft-sleeve function is that of protecting the shaft from

wear at a stuffing box (See Fig. 6.4).Sha'ft sleeves serving other functions

PAGE 26

are given specific names to Indicate their purpose. For example, a shaft sleeve used

between two multistage pump impellers in conjunction with the interstage bushing

to form an interstage leakage joint is called an interstage or distance sleeve.

6.4 Bearings

The function of bearings in centrifugal pumps are :

Reducing frictional force.



To keep the shaft in correct alignment with the stationary parts under

the action of a radial and transverse loads.

In horizontal pumps the bearings are usually designated as inboard and

outboard. Inboard bearings are located between the casing and coupling. Because

of the heat generated by the bearing itself or the heat of the pumped liquid (more

than 120"C), the bearing temperature are kept within proper limits (40* C to 60" C)

either by a forced feed lubrication system @incorporatina oil ..ooieror by Jacket

cooling. All type: of bearings are used in centritugai :)umps depending on the

service conditions.

6.5 Punip Sealing

Sealings are provided to prevent any leakage at the point where the pump

shaft passes out through the casing. The pump seals prevent air leakage into the

pump if the pump pressure is less than atomospheric and if the pressure is above

atmospheric the function is to prevent the liquid leaking out of the pump.

Basically two types of sealings are used

Stuffing Box

Mechanical seal

6.5.1 Stuffing Box

A stuffing box consists of a number of rings of packing around the pump

shaft housed inside a cylindrical recess between the pump casing

PAGE 27

and the pump shft. The packing is compressed to give the desired fit on the shaft by

a gland that can be adjusted in the axial direction. Fig. 6.5 a It sealing the box is

desired, a lantern ring(Fig. 6.5 b)is used that separates the rings of packing into

appoximately equal sections.



Fig. 6.5 a Conventional stuffing box with bottoming ring.

Fig. 6.5 Lantern gland or seal cage PAGE 28

6.4.3 PACKING PROCEDURE OF GLAND PACKING :

(A) PREPARING THE EQUIPMENT

1. With the pressure off the stuffing box, and liquid drained where necessary, remove

the gland follower nuts and null the gland follower clear of the stuffing box.

2. Carefully withdraw the old packing, using paired extractor tools of the correct size,

placed on opposite sides of the shaft. Remove any vestiges of the old packing and

wipe the stuffing box clean.



3. Check the shaft to concentricity with the stuffing box bore.

4. Check the shaft to ensure run out does not exceed 0.025 mm T.I.R.

5. The shaft surface in way of the packing rings must be free from scars, pitting, grooves

or ridges.

PAGE 29

6. Examine the gland follower for general condition and fit. The inner radial clearance

should be .25 mm to .4 mm maximum and the outer radial clearance should be .25

mm maximum., to prevent risk of cocking or touching on the shaft.

7. Check the clearance between the neck bush and 'the r 1 haft. If this is greater than

.25 mm radiaily. it may be advantageous to employ a tin, close clearance spacer

ring in the bottom of the stuffing box, to prevent risk of packing extrusion.



(C) PARKINGS

1. Gland packings are normally supplied as spirals or on a spool or coil, or as die-

formed rings made to specified dimensions. When specified as a continuous length, it

is necessary first to cut off the length of material to make the required number of

rings.

2. Place the packing round the shaft, or a- mandrel of the specified diameter. (The bore

of metallic and intruded packing spirals should conform to this diameter).

3. To assist in cutting. rings, two guide lines parallel, to the shaft axis and separated by

a distance equal to the packing section may be drawn on the spiral.

PAGE 30

4. Cut the rings from the spiral at an angle of 45' diagonally across the guide lines - no

gap is left between the ends.



5. Metallic and extruded packing rings are, spirally opened ready for fittings by pulling

the ends axially apart.

6. Check the first ring to ensure a correct fit in the stuffing box, before cutting further

rings in the same way.

(C) FITTING THE PACKING

1. Check the shaft to ensure it turns freely.

2. Fit each packinq ring individually.

3. Joints are staggered by 120'.

4. Check the shaft to ensure it can be turned. afte@ fittina each packing ring.

5. If alantern ring is fitted, it must be correctly Positioned below the inlet connection

allowing for slight compression of the bottom Packing rings. Bring the gland

follower up squarely against the last packing ring and tighten the nuts to finaer

pressure.

6. Tighten the nuts finally aftpr charqinq the valve.



PAGE 31

6.44 SUMMARY OF PACKING TYPES AND PROPERTIES Type Material Construction Temp. (Max.

of range) Maximum pressure

PH Suitable for

0F 0C lb/in2 bar

Natural fibre Cotton Plaited or bri- ded with lubricant

199 90 - - 6-9 Water

Hemp Plaited or bri- ded with lubricant

176 80 - - 5-9 Water

Flex Plaited or bri- ded with lubricant

160-250 70-120 - - - Water

Synthetic fibre

Nylon,rayon etc.

Plaited or bri- ded impregnatedwith PTEE

Not used for valve packing

Asbestos White asbestos

Plainted or braided with graphite, mica or,oil lubricant

-22 to 570

-30 to +300

5-12 Steam, liquors,etc.

Asbestos (reinforced)

White asbestos, inconel wire reinforc- ement

Plaited or braided with graphite, mica or oil lubricant

-60 to +1380

-50 to +750

3600 to 9500

250 to 650

4-11 Water,steam solvents, hydrocarbons incorporating acids and alcohols

Asbestos graphite

Asbestos fibres mixed with graphite

Wet-spun,dust free type preferred as smoother than dry mix.

-30 to +570

-40 to +300

5-12 High temperaature and stem services.

PTFE PTFE yaarns or tape

Plainted or braided

-328 to +490

-200 to +250

0-14 Water,steam, hydro-carbon, soft packings

PTFE yarns with lubricant



PAGE 32 PTFE yarns,

treated with PTFE dispersion

Plaited or braided

-328 to +570

-200 to +300

1450 100 0-14 All media, but little used for valves.

PTFE / graphite

PTFE / graphite mix

Solid extrusion

+480 +250 1450 100 0-14 Water,oils hydrocarbons alkalis, acids, alcohols etc.

PTFE / aramid

Aramid fibres treated with PTFE dispersion

coated fibres braided or plaited and impregnated with lubricant

-364 to +570

220 to +300

2900 to 14500

200 to +1000

1-14 Not particularly suitable for valve stem seals.

Expanded graphite

Pure expanded graphite

Tape form -328 to +1100

-200 to +600

4350 300 0-14 High temperature services sealing gases and low

pure expanded 'graphite

Flexible plait -328 to +1100

-200 to +600

4350 300 0-14 Viscosity fluids : all services requiring superior leak tightness.

Carbon fibre Amorphous carbon yarns treated with graphite powder

Twisted or plaited

-328 to +1100

-200 to +600

0-14 High temperature services but little used for valves

Glass fibre Glass fibre yarns

Braided with added lubricant

Corrosive media (except strong alcohols)

Alumina silicate

Alumina silicate

Plaited,with or without inconel wire rein forcement

2300 1260 0-9 Extremely high temperature services.



PAGE 33

6.5.2 Mechanical Seals

The stuffing box cannot provide minimum leakage because to lubricate the

shaft and the packing, the pumped fluid must be allowed to leak out of the pump.

The packing requires periodic tightening. This leads to frictional losses and

consequent failure of the stuffing box.

In order to avoid the above, the mechanical seals are used. In mechanical

seals, the sealing surfaces are located in a plane perpendicular to the shaft.

Mechanical seal essentially consists of two, highly polished surfaces running

adjacently, one surface being placed on the shaft and the other to the stationary

portion of the pump. The lapped surfaces, made of dissimilar metals are held in

continual contact by the spring, forming fluid tight seal between the rotating and

stationary members with very little frictional losses. Fig. 6.7 shows the details of

mechanical seals of a KH 1 Boiler Feed pump.

6.5.3 Cooling of Mechanical Seals

There are a number of reasons for cooiing mechanical seals :

To prevent the destruction of the liquid film between sealing faces due to

high temperature

To prevent vaporization of the liquid at the seal faces

To protect the seal faces by oreventing overheating and continuous flushing

Basically there are two types of seal arrangements-internal and External.

Internal assembly is the one of which the rotating element is located inside

the box and is in contact with the liquid being pumped Fig. 6.6A

In External assembly the rotating element is located outside the box Fig. 6.6 b.



PAGE 34

PAGE 35

Both internal and external types always have three primary points Fig. 6.8 at which

sealing must be done as described below:

Point (1) - Between the stationary element and casing. This point. is sealed by

conventional gaskets or some synthetic 'O' ring.

Point (2) - Between the rotating element and shaft (or shaft sleeve). This point is sealed

by '0' rings, bellows or some form of flexible wedges.

Po i nt (3) - Between the mating surfaces of rotating and stationary seal elements.

Leakage between these two surfaces cannot be entirely stopped but can be

reduced to insignificant amount by maintaining a very close contact.



Whenever the temperature of liquid being pumped is above 7@ C, the thin film of

liquid entrapped between the seal faces flashes into steam because of rise of

temperature in the seal faces due to friction. This causes the seal faces to wear very

rapidly.

So, it must be ensured that liquid around seal area is limited to 7@C. While pumping

liquid at 70" C or more, arrangements must be made to cool the seal faces either by

flushing the seal faces with external cold water or by a close circuit sealing system

with external cooler.

PAGE 36

6.6 Wearing Rings

Wearing Rings are used between the pump casing-and impeller to provide a

leak tight joint using renewable parts. The wearing ring can either be fixed to the

casing or to the impeller and in some cases it is a double ring fixed to both impeller

and the casing.

There are various types of wearing ring design and selection of a type

depends on the liquid handled, the pressure differential across the leakage joint, the

rubbing speed and pump design. The various designs are shown in the Fig. 6.9 .

These designs are based on the variation of the leakage joints to provide

resistance to leakage, flow from high pressure discharge side to low pressure suction

side.

The clearance between the wearing ring mounted on the casing or casing ring and

the impeller is a function of the leakage joint, diameter.



PAGE 37

7.0 Axial thrust & hydraulic balancing

Axial thrust is the summation of unbalanced impeller forces acting in the

axial direction.

7.1 Axial thrust in single-stage pumps

The ordinary single suction radial flow impeller, with the shaft passing

through the impeller eye, is subject to axial thrust because a portion of the front

wall. is exposed to suction pressure.

Thus the net axial force will be acting towards the suction side and it will be :

(Pd - Ps) x hub area, where Pd' = discharge pressure and Ps = suction side pressure

Fig. 7.1,.

A double-suction impeller is axialy balanced with the pressure orv one side equal to

that on the other side Fig. 7.2 . Though this is theoretically true, in practice even in the

double suction pump axial unbalance persists. To compensate for this, all centrifugal

pumps incorporate thrust bearings.



PAGE 38

To eliminate the axial thrust of a singte-sijction impeller, a Pump can be provided

with both front and back wearing rings. To equalise thrust areas, the inner diameter of

both rings is made the same. Pressure approximately equal to the suction pressure is

maintained in a chamber located on the impeller side of the back wearing ring through

drilled balancing holes through the impeller Fig. 7.3.

Leakage past the back wearing rings is returned into the suction area through these

holes. In case of large single-stage single-suction pumps, balancing holes are replaced

by a piped connection to the pump suction.

7.2 Axial thrust in multistage pumps

A multistage pump essentially consists of a number of singie-stage impellers

mounted on the same shaft.

Single-stage impiollers can be mounted in two ways

i) Several impeders mounted on one shaft each having its suction and facing

in the same direction and its stages following one another in ascending

order of pressure. The axial thrust is then balanced by hydraulic balancing

device.

PAGE 39

(ii) An even number of single-suction impellers can be mounted half in one

direction, half in opposite Erection. With this arrangement, axial th. rust-on



the one half is compensated by the thrust in the opposite direction on the

other half.

7.2.1 Hydraulic balancing devices

Hydraulic balancing devices are mostly used in multistage pumps to balance

the axial thrust and to reduce the pressure on the stuffing to the fast-stage impeller.

This hydraulic balancing device may be a balancing drum, a balancing disc or a

combination of the two.

7.2.2 Balancing drum

Balancing chamber is provided after the fast stage impeller. The chamber is

separated from the pump interior by a drum that is either keyed or screwed to the

pump shaft and hence it rotates with the shaft. The drum is separated by a small

radial clearance from the stationary portion of the balancing device. The balancing

chamber is connected either to the pump suction or to the vessel from which the

pump takes its suction. Thus, the back pressure in the chamber is slightly higher

than the suction pressure Fig. 7.4).

The forces acting on the balancing drum are the following :

i) Towards the discharge end -F, = Pd x front balancing area

ii) Towards the suction enct.F2 = Pb x back balancing area,

Pb = back pressure, Pd = discharge pressure.

The first force is greater than the second thereby counter balancing the axial

thrust exerted.

Since 100% balance@ is unattainable in practice, the balancing drum is often

designed to balance only 90 to 95% of total impeller thrust.



PAGE 40

However, the major disadvantage of balancing drum, is that it does not compensate

automatically for any change in the axial thrust caused by varying pump operating

conditions.

7.2.3 Bglgncing disc

In this case balancing disc rotates with the pump shaft and it is separated

from the balancing disc head (stationary part) by a srnall axial clearance. The

leakage through this clearance flows into the balancing chamber and from there

either to the pump suction or to the vessel from which the pump takes its suction.

The back of the disc is subject to the balancing chamber back pressure,

whereas the disc face experiences a range of pressures (discharge pressure at its

smallest diameter to back pressure at its periphery). The inner and outer

diameters of the disc are so chosen that the total force acting on the disc face and

that acting on its back wall will balance the impeller axial thrust Fig. 7.5.

If the axial thrust increases during operation, the disc moves tovvards the disc

head reducing the axial clearance. This will result in reduction in leakage and

hence in the back pressure in the balancing chamber. This automatically

increases the A p acting on the disc and moves it away from the disc head,

increasing the clearance. Now, the pressure builds up in the balancing chamber

and the disc is again moved towards disc head until an equilibrium 1 is reached.

Thus automatic compensation is ensured.



PAGE 41

The disadvantage of a balancing disc arrangement is that the pressure on the

stuffing box packing is variable and this is quite detrimental to the life of packing.

7.2.4 Combination of balancing disc and drum

The combination of balancing disc and drum is developed to overcome the

shortcomings of the disc while retaining the advantage of automatic compensation

for any axial thrust changes Fig. 7.6).

7.2.5 Balancing device in Boiler Feed Pump

The axial thrust in case of a BFP type 200 KHI/150 KHI(BHEL)

isapproximately 34 tons and is balanced by the provision of balancing device. It

consists of a rotating balancing disc with a small axiai clearance of 0.08 to 0.12mm

against a static balancing disc. A part of the higli pressure water a fter the last

impeller is allowed to pass through the throttling bush and to act on the front surface

of the balancing disc. The back surface of the disc is exposed to suction pressure by

connecting the space behind the disc to deaerator through piping. The difference in

pressure on both sides of the disc exerts a thrust on the disc and tries to move the

entire rotor towards right. Since this force is opposite and equal to axial thrustthe

rotor comes in equilibrium position maintaining the clearance of 0,08to 0.12mm

depending on the type of pump i.e. 200 or 150 KH 1.

PAGE 42

8.0 Pump Maintenance



8.1 SAFETY : While taking up any maintenance job the related safety aspects should

always be kept in mind and never be ignored. Following steps must be observed'

1) Obtain a 'permit to work' from competent authority, Permit must specify the

pump(s) to be taken up for maintenance, inform the steps to be taken for

isolating the pump from the system.

2) Ensure that isolation is actually carried out as per the instructions.

3) Drain the pump and connected pipe line before working and be sure of the

nature of the fluid being carried through the pipe. If the line handles liquid of

corrosive nature use required personnel protective equipment.

4) Allow the pump to cool down sufficiently.

5) Clean the surrounding area, make proper access to the working place. Take

care of other hot lines, if any, around the pump.

6) Choose right tools. Consult manufacturers instruction for special tools, if

required.

7) Allow only authorized persons in the work area.

8.2 Maintenance operations for centrifugal pumps fall into two categories

a) Routine preventive maintenance

b) Major overhaul or Repairs

Routine Maintenance

Routine maintenance can be classified as work done primarily to rectify the

effects of normal wear in a pump.

Overhaul or Repair are carried out to rectify the results of excessive wear,

over heating, damag e from solids in the liquids or injury or wear due to any other

cause.

PAGE 43

A maintenance record for the pump must be kept and preserved to monitor

machine performance

Maintenance Intervals

The usual intervals recommended for routine preventive maintenance are monthly,

quarterly, half-yearly and annualiv, Theseare satisfactory for all common

centrifugal pumps, provided hourly checks are regularly carried out.

8.2.1 Daily Observation of Pump Operation



When operators are on constant duty, hourly and daily inspections should be

made, and any irregularities in the operation of a pump should be reported

immediately. This applies particularly to changes in the sound of running pump,

abrupt changes in bearing temperatures, and stuffing box leakage. A check of the

pressure gauges and of the flowmeter ,,if installed, should be made hourly. If

recording instruments are provided, a daily check should be made to determine

whether the capacity, pressure or power consumption indicate that further inspection

is required.

8.2.2 Monthly Check

Use a thermometer to check temperatures of each bearing of the pump.

Temperature, in no case should go beyond 720C. Before allowing any bearing to

operate at any temperature above that recommended, check with the pump

manufacturer. Much depends upon the type of bearings, its lubricant and the duty

the bearing performs in the pump. In bigger size pumps on line temperature

measuring points are provided for this purpose.

8.2.3 Quarterly

a) Check oil & Replace

Once in every 3 months, drain the oil from sleeve type bearings. Washout

the oil wells and bearings interior parts with kerosene oil. Check the oil rings.

b) Check bearing lubrication, arrangements

Rings must be free from all the dirt, completely circular and must turn freely

when the pump shaft is rotated. Repair or replace any defective oil rings. Refill

the bearing with the correct oil.

PAGE 44

c) Check Grease for Specifications

Inspect grease lubricated rolling contact and sleeve bearings for

saponification, a condition revealed by a whitish colour of the grease. It is caused

usually by leakage of Water or other liquids past the bearing shaft seal To relieve

this condition, flush all grease from the bearingluse clean warm Kerose@ne oil to

do the same. When the bearing is clean atid dry, replace it with new clean grease of

recommended grade.

d) Measure bearing clearance



Place three length of metallic packing or plastic wire on top of the journal.

The wire should not be more than 0.20 mm thicker than the estimated clearance.

Replace the bearing cap and tighten its hold down nuts.

Remove the cap and measure the thickness of each of Flattened wire with

micrometer. If all leads are of the same thickness, the clearance is uniform,

throughout the bearing.

Thickness of any wire gives the bearing clearance at the point at which wire

was located. Check the clearance, and enter it in the pump record card, along with

the date of the replacement.

8.2.4 Half Yearly

Good, stuffing box must leak

Check the shaft packing by observing the leakage from it, leak should be 40

to 60 drops per minute for adequate cooling, this may vary with pump service

conditions, liquid handled and the type of the packing used.

If rate of leakage is higher than the recommended one check packing, and

replace all. Don't replace one or two packs.

Removal of old packing

Remove packing by extractor. Make sure that shaft is not scratched while

removing worn out packing.

Note down seal position

If seal cage or lantern ring is provided, note down its position. Count the

number of packing in front. or in the rear side of the seal cage.

PAGE 45

Check Shaft sleeve

Check the shaft sleeve for wear. If the sleeve is badly scarred or worn,,

replace it.

To slip the sleeve from the shaft, use sleeve puller. If there is some

difficulty, apply some heat on the sleeve and pull by puller.

Check run out of the Shaft.

If packing wear is more, and sleeves are in good condition, check the shaft

run out, use Dial Test Indicator (DT I).



Check with D.T.I. and if run out is more than the permissible limits get your

shaft straightened

Find out right size of packing thickness

Measure the stuffing box bore, subtract the shaft diameter. Divide bv 2, to

find out the right size of the packing to install.

Stagger the joint at :

a) 1800' if the stuffing box has two packings

b) 120 if the stuffing box has three packings

c) 9011 if the stuffing box has four packings

Insert packings and be sure that packing has reached its proper place.

Locate Lantern Ring

Be sure each ring is firmly seated before the next one is inserted. Locate the

Lantern ring, it lines up with the centre of the cooling liquid opening. Remember

the ring moves back into the box as the packing is compressed. Allow the packing

to leak until it seats itself. As the packing, is being installed, turn the shaft by hand

in the normal direction of rotation to level off any high spots in the packing.

Gland Adjustment

Tighten the packing gland just enough to prevent excessive leakage before

starting the pump. As the packing adjust itself in the shaft, tighten the gland slowly,

one flat at a time until the desired results are achieved.

PAGE 46

Do not back off the gland nuts

Do not back off the gland nuts, while the pump is running. This will allow

the entire sets of rings to move away from the bottom of the box without relieving

pressure of the packing on the shaft sleeve. The best islif packing is too tight,to stop

the pump, and allow the stuffing box to cool, and then readjust the packing. Start

the pump and check stuffing box temperature. It may be necessary to stop and start

pump several times before the proper leakage and temperature is obtained.

8.2.5 Annual Inspection

Centrifugal pumps should be very thoroughly inspected once a year. In

addition to the semi annual maintenance procedure the bearings should be removed,

cleaned and examined for flaws. The bearing housings should be fully cleaned.



Antifriction bearings should be examined for scratches and wear after cleaning.

Immediately after inspection, antifriction bearings should be coated with oil or

grease to prevent dirt or moisture from getting into them.

The packing should be removed and the shaft sleeves, or shaft, if sleeves are

not used, should be examined for wear.

The coupling halves should be disconnected and alignment checked. In the

case of horizontal pumps with babbitt bearings, the vertical shaft movement for both

ends should be checked with the packing out and the coupling disconnected. Any

vertical movement more than 150 per cent of the original play reuires investigation

to determine the cause. If the end play is higher than allowed and recommended by

the manufacturer, the cause should be determined and corrected.

Drains, sealing water piping, cooling water piping, and other piping should

be checked and flushed. If an oil cooler is used, it should be flushed and cleaned.

The pump, stuffing boxes should be repacked and the coupling reconnected.

If instrument and monitoring devices are available, these should be

recalibrated and a test made to determine whether proper performance is obtained.

If internal repairs are made, the pump should again be tested after completion of the

repairs.

PAGE 47

8.3 Complete Overhaul

General rules cannot easily.be made to determine the proper frequency and

regularity of complete overhauls of centrifugal pumps. The type of service for

which the pump is intended, the general construction of the pump, the liciuid

handled, the materials used, the average operating time of the pump, and the

evaluation of overhaul costs against possible power savings from renewed

clearances, all enter into the decision on the frequency of complete overhauls. Some

pumps on severe service may need a complete overhaul monthly, whereas other

applications only require overhaul every two to four years or even less. frequently.

8.3.1 Stages of Major Pump Checkup

1 . Stripping the pump

Identification and marking of parts

2. General Inspection of parts removed.



3. Specific fault detection.

4. Rectif ication of fau Its,

Bearing housing

Bearing replacement

Neck ring clearance

lmpeller condition

Changing gland packing

Check shaft for straightness

Keyways and keys

Shaft sleeve tolerances

Condition of nuts & bolts

5. Condition of gland and gland housing (Clearances)

6. Assembly of pumps

7. Pump alignment

PAGE 48

8.3.2 Method of Marking or Stamping items when Stripping Pumps

Stamping the Pump

1 Clean pump, motor, bedplate etc.

2. Remove any klinger cocks, valves, gauges, tundishes etc. from pump body.

3. Check if any existing marks or stampings are visible on pump, body,

couplings, gland etc.

It may be possible to use original stamping and so not to confuse when

rebuilding pump

4. Stamp glands.C.E. (coupling end) or C.D.E. (Coupling drive end) and B.E.

(back end) or N.D.E. (non drive end).

5. Stamp pedestal caps and bearings C.E. or C.D.E. and B.E. or N.D.E. on top

and bottom halves.

6. Stamp bearing housings. C. E. or C. D. E.' and B. E. or N. D. E.

7. Mark any covers to be removed including the top cover of single and twin

stage pumps.

8. All parts not suitable for stamping must be marked or lables attached i.e. oil

rings, junk rings, lantern rings, water or oil throwers, ball and roller



bearings, sleeve nuts etc. and ail dowels removed from covers or feet of

pumps.

9. All bushes and neck rings must be stamped or marked from coupling end of

pumps.

10. When marking a multi-stage pumpchambers should be stamped from

coupling end of pump i.e. suction chamber is No. 1 chamber and so on.

(See. Fig. 4).

11. When marking impellers, the impeller whose necking enters suction

chamber should be marked or stamped on the delivery side of impeller.

12. All keys should be stamped from coupling end i.e. (coupling key) No.l. (No.

1 lmpeller) No. 2., (No. 2 ]mpeller) and so on right up to B.V. (Balance

Valve) Key.

13. All chamber plates should be stamped from coupling end i.e. suction

chamber plate No. 1 and so on.

14. All neck rings and bushes removed from chambers or plates should be

stamped from coupling end of pump as they will be used for reference.

15. Any Guide vane tips removed from chambers must be stamped for

reference use numbered from suction end.

PAGE 49

8.3.3 Complete Dismantli g of A Centrifugal Pump

Centrifuga pumps should be dismantled with great care. The suction and

discharge valves should be-closed and the pump casing drained. All necessary

piping and parts that would interfere with thd disassembly of the pump, such as

bearing covers, should be taken apart as required by the manufacturer's instructions.

The upper half of pumps with axially split casings should be lifted straight up

after the dowels and the nuts of the casing bolts have been removed, to prevent

damage to internal parts. The rotor should also be removed vertically to prevent

injury to the impellers, wearing rings, and other parts.

During the dismantling procedure, the various parts removed must be marked

to ensure proper reassembly. All individual parts and all important joints should be

carefully examined. If the pump has been operating satisfactorily with only a slight



reduction in head and capacity due to increased leakage, a decision on

reconditioning will depend on several factors- like

Availability of spare parts.

Length of time the pump can be left out of service.

Economic considerations and importance of getting the service from the

unit without overhauls.

Generally, worn parts should be renewed if the pump is not to be examined

until the next routine period, regardless of the performance of the unit, because

when parts in new or good condition are assembled in contact with dirty or worn

parts, the new parts are very likely to wear out re-Pidly.

8.3.4 Maintenance of specific pump parts

i.) Special care is required in the reassembly of multistage pump rotors with

axially split casings. These casings are made from castings and, when the

pump is built, it is sometimes necessary to allow variations in longitudinal

dimensions on the casings. This is done by making assembly floor

adjustments to the rotor, in order to preserve the designed impellers in their

correct positions, with respect to their volutes or diffusers.

ii.) When making field renewal of rotors or of stationary parts, all lateral

PAGE 50

distances should be compared with those on the old parts and where lateral

end movement is affected, these distances should be duplicated.

iii.) The assembled rotor and stationary parts (such as casing wearing rings,

stag-pieces, diffusers) $hould be placed in the lower half of the casing and

the total lateral clearance checked.

iv.) When the thrust bearing is assembled and the shaft is in its proper position,

this total clearance should be suitably divided and the impeliers centrally

located in the volutes or diffusers. The shaft nuts can be manipulated for

final adjustments.

v.) To avoid shaft distortion, all abutting joints must be square with the shaft

axis and with each other, and the impeller and shaft sleeve nuts must not be

tightened with excessive force. Otherwise, the metal may be crushed at

these joints, exerting severe moments on the shaft. ]'he shaft may become



bowed under the influence of these moments and develop a marked

vibration, in addition to the possibility of rubbing and binding at the

internal running joints.

vi.) When using locking screws of the safety, type, the assembly should be

cheked using a dial,test indicator, to make sure that the shaft is not bent in

its bearings or on centres to check for eccentricity and any eccentricity

corrected.

8.3.5 Pump reassembly :

If the pump casing is split axially, great care must be exercised in replacing

the upper casing half and tightening up the casing bolts.

ii) If more than one row of bolts is used, the row nea rest to the pump central

axis should be tightend up first. After all the bolts have been tightened once,

they should be tightened again to ensure the tightness of the casing joint.

iii) They should then betightened once more when the pump has been brought up

to operating temperature.

8.4 Spare and reoair parts

The service for which a centrifugal pump is used will determine, to a great

extent, the minimum number of spare parts that should be carried in stock at

the installation site.

PAGE 51

Average minimum for any centrifugal pump should include a set of wearing

rings, a set of shaft sleeves (or a shaft if no sleeves are used) and a set of bearings.

It is often advisable to carry a complete spare rotor for installation in the pump when

examination shows that the pump rotor has become excessively worn, or if it

becomes accidentally' damaged. Sufficient spare packing for the stuffing boxes and

material for the gasket of axially split casing pumps should always be in stock.

Spare parts should be purchased at the time the order for the complete unit is

placed. Depending upon the contemplated method for wearing ring overhaul, the

spare wearing rings are ordered either same size as the wearing rings used in the

assembly to the new pump or bored undersize.

8.4.1 How to Order for Spares :



The pump serial number and size as stamped on the manufacturer's

nameplate should always be given when ordering spare and replacement parts, This

needs to be ensured so that the manufacturer may identify the pump and furnish

repair parts of correct size and materials. Most centrifugal pumps are of standard

design and a great number of combinations are made for each size of casing, using

different impeller. sizes and designs. Without an identification number, the pump

manufacturer would be at a loss to furnish correct spares even though size and type

of the pump might be known. Some manufacturers issue special formats for

ordering spares. If available, they must be us--d.

8.5 Record of inspection and repairs:

The working schedule of the half yearly and annual inspection programme

should be incorporated on maintenance cards, one for each pump in the installation.

These cards should contain the pump identification number, the date of the

scheduled inspection, a complete recrod of all the items requ@ring individual

inspection, and space for comments and observations of the inspecting personnel.

Adequate maintenance does not end with repair work on worn or aamaged parts. A

written record of the conditions of the parts to be repaired or replaced, of the rate

and appearance of the wear, and of the method by which the repair was carried out

is as important as the repair job itself. These records\can form the basis of

preventive measures which will act to reduce both the frequency and cost of

maintenance work. The type of inspection records and the extent of detail they may

contain vary with the type of pump in question and availability of personnel.

PAGE 52

It is often advisable to take photographs of badly worn parts before they are

repaired, photographs provide more accurate and more graphic record of the damage

than a description.

Complete records of maintenance and repair costs should always be kept for

each individual pumps together with a record of its operating hours; study of these

records may reveal whether a change in materials or design will be the most

economical plan to follow.

8.6 Major Repairs and Overhaul



Apart from the regular maintenance discussed earlier, the pump may require

repairs or major overhaul, Repairs pertaining to each components are discussed

here.

8.6.1 Casing Repair :

Some time casing develops vapour lock conditions as shown in the Fig.

8.1(A, B). This cannot be removed even after repeated priming. This may be found

in the volute casings. Under such case the gas/vapours entrapped is to be removed

by drilling a hole of suitable size as shown in Fig. 8.1'(A, B) at suitable location.

PAGE 53

8.6.2 lmpeller Maintenance

An impeller removed from the pum p casing should be carefully examined on

all surfaces for Unusual wear, such as abrasion, corrosion or cavitation. Most pump

for general service use bronze impellers which has a reasonably long life.

Occasionally, these pumps operate on high suction lifts or at part capacities both of

which affect impeller, life. Pumps handling water containing sand may use bronze,

cast-iron, nickle or even chrome steel impellers depending upon the amount of sand,

its abrasiveness and the character of the water.



Generally, impeller materials that form a protective coating or film, which

adheres firmly to the underlying metals and is not washed off by the water stream,

should always be used. However, abrasive material naturally erodes this protective

film on many metals making their use undesirable.

Abrasion wear can be best tested by a sedimentation test. Some of the

pumped liquid is allowed to stand in a glass container for a few hours, and the

settled particles are examined for grit. A chemical laboratory analysis of the

pumped liquid is usually necessary to determine whether corrosion is responsible for

wear. Of course, if corrosion wear is detected, the substitution with better materials

becomes necessary.

Cavitation is often accompanied by pitting in the impeller suction areas and

can be detected by a crackling noise during operation. If impellers rapidly become

pitted or eroded, the increased cost of special alloys is often warranted.

In small pumps, impeller wear is best corrected by replacement of the

impetier, because the pump size does not permit its being rebuilt. Whereas

rebuilding by brazing, soldering, welding etc. is feasible, the cost is high and so

replacement is usually the better solution.

Most large impellers will -provide many years of service, regardless of

abrasion, if eroded a,-eas are treated by 'building up' the metal. Although unlikely

wear may sometimes occur in the impeller hub over the shaft mounting'or at the

keyway. The first may be caused by a porosity in the impeller casting, permitting

water to seep from the higher pressure region to the fit between the shaft and

impeller. Sometime, the shaft material is the one more readily attacked. Wear at

the keyway may occur if the impeller fits loosely on the shaft or the key is not

properly fitted.

PAGE 54

Finally, impeller cracks may develop because of excessive vibration or

strains set up during the casting process and not detected at the time the impeller

was machined. Cracked impellers cannot be successfully repaired and are best be

replaced.

lmpeller balance should be rechecked 'whenever'the impeller is removed

from the pump rotor during overhaul. For balancing by hand, the impeller is



mounted on an arbor, the ends of which are placed on two parallel and level knife

edges. If the impeller is out of balance, it will turn the arbor and come to rest with

its heavy portion down. Metal must be removed from this portion in such a way that

pump performance will not be affected and so eddy currents, which accei,-rate

erosion, will not result. For these reasons, drilling holes in the excess metal is

undesirable.

For balancing a shrouded impeller, the best practice is to mount the impeller

off-centre in a lathe and take a cut (which will be deepest at thp. periphery) from the

shroud . The cut can be taken from both shrouds, depending upon their actual

thickness and the amount of metal to be removed.

In semiopen impetier pumps, the removed metal can be taken from the

shroud if the design permits or from underneath the vanes if those on the heavy side

are th.icker than the others. The latter method is the one used for balancing open

impellers

8.6.3 Wearing Ring Maintenance

8.6.3.1 Installation

Most rings are now pressed on the impeller As distortion may occur during

the mounting process, it is advisable to Check the shaft and impeller assembly on

centres to see if the new ring surfaces are true and if not, to true them up. If the

proper facilities are available, it would be just as easy to get slightly oversi7P rings

and turn their wearing surface to the proper diameter after mounting.

8.6.3.2 Clearance

One manufacturer's clearance and tolerance standards for nongailing wearing

joint metals in general service Pumps are shown in Fig. 8.2. They .apply to the

following combinations - i). Bronze with a d issimilar bronze

PAGE 55

ii). cast iron with bronze, iii). steel with bronze, !v). monel metal with bronze, and v).

cast iron with cast iron. If the metals gall easily (like the chrome steels), the values

given should be increased by about 0.002 in. In multistage pumps, the basic diameter

clearance should be increased by 0.003 in. for larger rings. The tolerance indicated is

'plus' (+) for the casing ring and 'minus' for the impetier hub or impeiler rings.



In a single-stage pump with a joint of nongailing components, the correct

machining dimension for ' a casing ring diameter of 9.000 in, would be 9.000 plus

0.003 and minus 0.000 in. and for the impeller hub or ring, 9.000 minus 0.018, or

8.982 plus 0.000 and minus 0.003 in. Actual diametral clearances would be between

0.018 and 0.024. Naturally, the manufacturer's reconify@e,@ ndation for ring

clearance and tolerance should be followed.

PAGE 56

8.6.3.3 Allowable wear

It is difficult to generalize on the amount of wear allowable before apump

should be dismantled and the wearing joint renewed, because too many factors ar 1

e involved. Internal leakage through the rings naturally means an efficiency tor,,;.

Ring renewal should be such that the overhaul cost will be offset by the power

savings. lhus, with constant use and high power costs, stified. The rule of thumb

that 100 percent more frequent renewal can be ju increase in ring clearance justifies

ring renewal can be used as a guide.

Even though the clearance is not excessive and the pump can be reassembled

without renewing the wearing ring joint, always check the impetier hub diameter

and the inside diameter of the stationary wearing ring for eccentricity of wear.

8.6.3.4 Measurement of clearance



Wearing ring clearances may sometimes be measured by inserting a feeler

arts. If the wearing ring is L type gaugebetween the stationary and rotating p and

the lip of the L prevents inserting thegauge@he clearance may be approximately

checked without dismantling the rotor, in the following manner:

i) Mount a dial indicator o n the impeller (as shown [email protected]) and with the

stationary ring resting on the impeiier wearing ring huo, set the dial reading to

zero.

ii) Without moving the impeller or dial indicator, push up on the stationary ring

from below and record the maximum dial reading. This corres- sponds to the

diametral clearance.

PAGE 57

(3) Repeat this operation for every clearance joint and make a record of all

readings.

This operation is best carried out, however, with the rotor removed from the

pump casing it is best suited to multi stage pumps because once the rotor is out of the

casing of pumps, the stationary rings may be freely removed and the clearance

determined by measuring the two diameters and calculating the difference.

One note of warning : This short-cut method gives no clue to the condition of

adjacent clearance sufaces. In other words, burrs, grooves, or indentations caused

by foreign matter passing through the clearances will go undetected, as will the

resultant damage to the surfaces.



If the pump has been dismantled, normal procedure is to measure independent

the ID of the wearing ring and the OD of the impeller wearing ring hub. Use inside

and outside micrometers respectively. Several measurements will determine

whether or not the wearing ring or impeller has become worn in an egg shaped

manner. The clearance is considered to be maximum difference between the

maximum ID and the minimum OD readings.

Clearances may also be measured directly by placing the impeller within the

wearing ring and moving it laterally against a dial indicator to determine total

diametral clearance. To determine inequality in wear around the circumference, the

impeller should be rotated and the dial indicator attached to several points of the

stationary part. If the pump has been dismantled, however, the 'difference' method

is more reliable.

The impeller and wearing rings should be at the same temperature before

measurements are made. Some high pressure and high-termperature pumps use

shrunk-on impellers tha.L must be heated before removal from the shaft to at least

204*C and possibtv to as much as 260"C to 3160C. These should be allowed to

cool down to about 49"C so that measurements can be made comfortably. But if the

wearing ring is at 27 0C, say, there will be a 2eC diff-erence betweenthe two parts

and this difference can be quite significant. This error will, of course, be magnified

if the impeller diameter is measured when it's temperature is even higher than the 49

0 C we have assumed.

This possibility of error is,frequently over-looked, as many people assume that

such a small difference in metal temperatures is not of consequence.

PAGE 58

8.6.3.5 Restoring clearances when no rings are used :

To restore the clearance between impeller and casing, when no ring

is provided, consider one of the following

i) buy new parts

ii) build up worn surfaces by welding,metal spraying or other means, or

iii) Install a wearing ring or rings if sufficient metal is available in the'casing

part or on the impeller hub.

8.6.3.6 Restoring clearances of pumps with single rings.



There are three ways to restore the clearance of a pump with single flat or L-

type wearing ring construction

a) Obtain a new casing ring bored undersize from the manufacturer. Then,

true up the impeller wearing ring hub by turning down in a lathe.

b) Build up the worn surface of the wearing ring by welding or metal spraying

so that it can be bored undersize. Then true up the impeller wearing ring

hub.

c) True up the wearing ring by boring oversize, buildupthe impeller wearing

ring hub, and machine to give correct clearance with the rebored ring.

The last two methods are difficult and are only practicable with larger pump and

that only if facilities allow work to be done on the premises. Usua lly building up the

impeller wearing ring hub by welding is also very cliffcult, and double ring construction

is preferred. The first method is generally the best.

8.6.3.7 Restoring clearances of pumps with double rings.

If the pump has double flat or L-type wearing rings, clearances may be

renewed by one of the following methods :

a) Obtain a new oversize impeller ring and use the old casing ring bored out

larger.

b) Obtain a new casing ring bored undersize and use the old impeller ring turned

down.

c) Renew both rings if necessary.

d) Build up either the casing or impeller ring by welding or metal spraying

PAGE 59

and machine the other part. By altering the ring buildup the original leakage joint

diameter can be closely maintained.

8.6.4 Shaft Maintenance

During pump overhaul the shaft should be carefully examined for any sign of

wear, or irregularities, especially at all the important fits, such as the lmpeller, hub

bores, under the shaft sleeves and at the bearings.

The shaft may be damaged by rusting or pitting caused by the leakage under

the impeller or shaft sleeves. It is important to check shaft under plain or

antifriction bearings.



Check shaft conditions at the keyways, twisting of the shaft, excessive

thermal stresses, corrosion or even a poor original fit may have loosened the

impellers resulting in key way wear.

After visual inspection, the shaft should be placed on centres and checked for

any concentricity.

If the cost of the new shaft is high and if proper facilities are available, a

worn out shaft, can be repaired by metal spraying and remachining. Such repairs

should not be undertaken without familarity with the shaft material and appropriate

metal spraying methods. After the shaft has been repaired, it must be checked for

possible distortion and then rechecked after complete rotor assembly to make sure,

that it has not been distorted by excessive tightening of the shaft nuts.

8.7 Aiknment of Pump and Driving Unit

The following procedures outline the recommended practice for checking

shaft alignment. This method is independent of the truth of the coupling or shaft

and is therefore not affected by canted coupling faces or eccentricity of the outside

diameter of the coupling. Further this procedure is the same between pump and

intermediate shaft and between the later and motor siiaft.

PAGE 60

Before commencing alignment, rotate each shaft independently to check that the

bearings run freely and that the shaft is true to 0.04 mm (0.0015 in.)or better.

Caution

Ensure that no damage can be caused when the pump shaft is turned.

Couplings should be loosely coupled and the halves must be free to

move relative to each other, otherwise gauge indications can be incorrect.

8.7.1 Angular Alignment

(a) Isolate the motor from its power supply.

(b) Check the distance between the coupling flanges.

Note :

The distance between the flange faces should be 5 mm.

(c) Clamp two Dial Test Indicators (DT1) at diametrically opposite points on one

half coupling, or to the shaft behind it, with the plungers resting on the back

of the other half coupling, as shown in Fig. B.4 @next page)



d) Rotate the coupling until the gauges are in line vertically, and set th e gauges

to read zero.

(e) Rotate the coupling through a half revolution (181f) and record the reading on

each DTI. The readings should be identical though not necessarily zero,

because of possible end float. Either positive or negative readings

areacceptable, provided they are equally positive or negative. Refer to

tolerances given, and adjust the position of one of the units if necessary.

(f) Rotate the coupling until the gauges are in line horizontally and reset the

pointers to zero.

(g) Repeat sequence (e).

PAGE 61

8.7.2 Radial Alignment

(a) Clamp a DT 1 to one half coupling or to the shaft, as shown in Fig. 8.5 with

the plunger resting on the rim of the other half coupling.

(b) Set the gauge to zero.



(c) Rotate the coupling and record the reading achieved at each quarter

revolution (90'). Any variation in the readings indicate a deviation

PAGE 62

from alignment, and the position of the motor must be adjusted until the readings are

identical or writhin the tolerances given.

8.7.3 Tolerances

It is difficult to lay down limits of accuracy within which adjustments should be

made because of the differences in the size and speed of units, but as a roagh guide it is

suggested it is suggested that when checking angulat alignement readings the following

variations can be tolerated :

PAGE 63

Couplings up to 300 mmdiameterO.05 mm

Couplings over 300 mm diameter ... 0.07 mm

In checking the radial alignment of shaft,readings varying by mo,,than 0.102 mm on

gauge i.e. 0.051 mm eccentricity call for adjustment.



These figures are suggested for speeds of 1,500 r.p.m. For speed ot 3,000

r.p.m. or over, a somewhat greater degree of accuracy should be maintained.

When the pump handles a liquid at other than ambient temperature or when it

is driven by a steam turbine, the expansion of the pump or turbine at operating

temperature will alter the vertical alignment. Alignment should be made at ambient

temperature, making suitable allowances for the changes in pump and driver

centertines after expansion takes place. The final alignmerit must be, made with the

pump and driver at their normal temperatures, and adjusted as required before placing

the pump into permanent service.

For large installations, particularly with steam-turbine-driven pumps, more so-

phisticated alignment'methods are some-times employed, using proximity probes arid

optical instruments. Such procedures permit checking the effect of

temperature.changes and machine strains caused by piping stresses while the unit is in

operation. When such procedures are recommended, they are included. in the

manufacturer's instructions.

When the unit has been accurately leveled and aligned, the hold-down bolts

should be gently and evenly tightened before grouting. The alignment must be

rechecked after the suction and discharge piping have been bolted to the pumps to test

the effect of piping strains. This can be done y oose,djng the bolts and reading the

movement of the pump, if any, with dial ind.icators.

The pump and driver alignment should be occasionally rechecked, for

misalignment may develop from piping strains after a unit has been operating for

sometime. This is especially true when the pump handles hot liquids, as the pump

should be disconnected after a period of operation to check the effect of the

expansion of the piping, and adjustments should be made tc compensate for this.

PAGE 64

9.0 Pump Bearings - Maintenance and Lubrication

9.1 The bearings used on most pumps can be divided into two general

classifications - Sliding contact and Rolling contpct.

Sliding contact bearings are called Jourriai uearings and rolling contact

bearing are called Antifriction bearings Fig. 9.1,



9.2 One should remember that Bearing Maintenace does not mean replacement of worn

out bearings oniy but proper storage, inspection and iubrication also.

9.3 Storage of Bearings

Rolling bearings are coated with rust proof compound before being

packaged, and can be stored in their original package for many years.

Bearings should be kept in a place where the relative ttumiditv does not

exceed 601/o and where the temperature is reasonably constant. Bearings are

marked with their storage life.such a 2. Z. indicate maximum life of 2 years.

PAGE 65

Ensure that bearings not in their o riginal package are kept clean, well

oiled or greased and wrapped in waxed paper to prevent rust.

9.4 Observation

What to look for during operation

(a) Listen

Place one end of a listening rod, against the bearing housing as close to the bearing

as possible. Place the ear against the other end and listen, if all is well a soft purring sound

will be heared. A damaged bearing gives out a loud noise often irregular and rumbling.

(h) F eel

Check the bearing temperature either by using sensitive chalk, or by thermometer or

-often by hand. If temperature seems unusually high or changes suddenly, it 'is an



indication that some thing is wrong. The reason may be insufficient or excess lubricant,

over loading, bearing damage, insu~ fficient clearance, pinching high friction in the seals

or heat supplied by an external source.

Remember that immediately after re-lubrication, there will be a natural rise in the

temperature, which may persist for one or two.days.

(c) Look

Ensure that lubricant does not escape through defective seals, or insufficiently

tightened plugs. Impurities generally discolour the lubricant making it darker.

Check seals conditions near the bearing and ensure that no hot or corrosive liquids

or gases penetrate in the bearings. Any automatic lubricating device. should be checked to

ensure their proper functioning.

(d) Lubricate

As per schedule

PAGE 66

9.5 Installing Plain Journal Bearings

9.5.1 Proper bearing installation techniques vary for different type of bearings.

Plain journal bearing are usually easier to install than antifriction bearings.

However, they require great care to ensure proper alignment during installation

because of their fixed or non-self-aligning construction. Proper alignment is

accomplished with the use of shims placed beneath the bearing face. If a

@journal bearings is of the split type, the upper half can be removed to check for

proper alignment after it has been installed and running for a short period of time.

A visual inspection of the bearing material will show misalignment, if any.

9.5.2 Improper alignment of a plain journal bearing is usually indicated by shiny or worn

spots on its inne.r surface. Because of its length, the inner bearing surface will not

show wear over a large surface, but rather at concentrated points. Misalignment that

show up as a wear-spot on one end of the inner bearing surface will be matched by a

wear-spot on the opposite side of the inner bearing surface at its other end.

9.5.3 Plain journal bearings should be inspected for wearing-in characteristics after a few

hours of running. They should then be aligned properly, and lubricated as

recommended. These simple procedures -can result in the elimi-, nation of plain

journal bearing problems for long periods of time.



9.6 Installing Antifrication Bearings

9.6.1 When roller or ball bearings are installed, misalignment may not be noticeable for a

period of time because of their ability to accept slight amounts of misalignment.

However, remember that even though ball or roller bearings may appear to operate

satisfactorily under misaligned conditions, their life will be shortened considerably.

9.6.2 A ball or roller bearing is designed to operate with the inner and outer rings secured

again st the shaft and housing, respectively. Although this can be accomplished in

several ways, the simplest is by an interference fit between the I.D. and-0.D. of the

bearing and the shaft or housing. The bearings are usually installed using an arbor

press to force them into place, as shown in Fig. 9.2. If an arbor press is not available,

a pipe or sleeve may be used. No matter how the bearing is installed, be sure that

the ring which is being forced in place is'adequately supported as shown in the

illustration.

PAGE 67

9.6.3 If the bearing or the shaft to which it is attached is too large to be set up on arbor

press, then a bearing puller can be used, see Fig. 9.3. Although a bearing puller is

used mostly to remove a bearing, it can pull a bearing into position as well.



PAGE 68

9.6.4 If the area of contact between the bearing inner ring and the shaft is quite large,

other means are used to make mounting the bearing easier. A bearing with a large

area of contact is classed as a shrink fit bearing. One method of installing the

bearing is to expand it by using heat. Then it is placed on the shaft in its proper

position and allowed to cool. As it cools, it shrinks tightly into the shaft. Another

method of accomplishing a shrink fit is to cool the shaft in dry ice and then install

the warrri bearing. If the interference is large, a combination method, using both

heat and dry ice, is necessary.

9.7 Mounting a Bearing

9.7.1 Before pressing the bearing into the shaft, several important conditions should be

satisfied :

(a) Cleanliness of the area is necessary to prevent contaminants from getting

into both the exposed and unexposed bearing parts.

(b) The bearing should be supported properly and pressure applied to the

correct ring of the bearing.

(c) Be sure the bearing housing or shaft is free or all scratches, burrs, or other

irregularities, such as being out-of-round.

(d) Give the shaft or housing a light coating of oil or graphite grease to ensure

easy installation and easy removal later on.



9.7.2 As the bearing is being pressed into place the area below the bearings should be

repeatedly checked for dirt or metal chips that could wedge between the bearing ring

and the housing, of bearing ring shoulder. These particles may not seem important,

but they often cause misalignment. On a large shaft 10, 12 or more inches in

diameter, a scrap of metal measuring one or two thousandths of an inch will not

cause much misalignment. However, if this same scrap were put under a bearing

that is only one inch in diameter a large amount of misalignment could occur.

9.7.3 After the bearing has been mounted on the shaft or in the housing, check it for free

movement. First make certain that your hands are clean and dry. Then grasp the

unmounted ring of the bearing between your thumb and forefinger and rock it gently

from side-to-side. On most bearings there wi ']I oe a slight movement when this is

done, but no more than that. Check the bearing for free movement before it is

installed. If. you have another new bearing available, compare the two. Next rotate

the ring slowly with

PAGE 69

your hands to make sure that it turns freely without any binding or noticeable

drag. If the bearing turns hard, binds, or drags in a particular spot, check it

for dirt or other obstructions. If the bearing can't be freed and there is no

evidence of an out-of-round shaft or obstruction, the bearing has to be removed

and replaced with a new bearing.

9.7.4 After the bearings have been installed and the machine re-assembled, it should be

tested. Running the machine without a load for a short period of time will.ensure

that all components are properly installed.

9.7.5 During this test run, check the bearings for noise, high operating-tem-erature, and

vibration. A high noise level indicates damage that might have occurred during the

installation, improper mounting, misalignment, and interference of the parts.

9.7.6 Some of the noises to listen for after the bearing is running (both free and under

load) include : a high pitched whine from interference or overload, a medium to low

pitched noise from bearing misalignment, rattles from poor fits or loose bearings ,

and a rumbling sound, caused by a poor finish on shafts or housings, or out-of-round

housings.



9.7.7 After the machine has been started up and the bearings run-in,the bearing

temperature may increase over what might be considered the normal bearing

temperature. This is a warning to the maintenance craftsman of either an excessive

amount of lubricant or too high an operating speed. If the unit is running under full-

load conditions, an increase in bearing tempe-rature can indicate a too-high

operating speed or overload. Sealed bearings normally have a high operating-

temperature during initial startup, but the operating temperature decreases as the

machine continues to run. If the operating temperature does not come down, the

machine should be shut off and allowed to cool. During this cooling-down period,

the grease tends to redistribute itself to properly lubricate the bearing. Then, when

the machine is restarted, the high temperature should not re-occur. If it does, check

the bearing thoroughly.

9.7.8 Particular attention should be given to any locking device used to secure the bearing

in place on a shaft. Manufacturer's instructions should be followed

PAGE 70

when tightening the locking device, whether it's a collar with setscrews or a

threaded, split inner-sleeve and locknut. If no instructions are given, only sufficient

pressure should be used to ensure that the locking device is drawn up softly. Once

the ring is locked to the shaft, no additional pressure should be used. Any effort to

squeeze the bearing inner-ring down may distort the inner race and cause an

irregular shape in the bearing raceway. Any locking washers stould be peened over

to prevent rotation of the locknut during operation.

9.8 Bearing Removal

Removal of the bearings is simply a reversal of the procedures used to install the

bearings. If the bearing is designed to be installed with an arbor press, then an arbor

press should be used for removing the bearing as shown in Fig. 9.4 If the bearing or

shaft is too- large to fit in a press a bearing puller can be used.



PAGE 71

If the bearing does not come off the shaft easily, a different approach has to be used.

One method is to use a torch to heat the bearing, which allows it to expand, thereby

increasing the clearance between bearing and the shaft. If you use this method,

exercise extreme caution during this procedure to ensure that any grease. or

lubricant in the bearing does not start a fire. Also, make sure that the heating torch

is the proper type and set for a heating flame and not a cutting or burning flame.

(Never use a cutting torch when only heat is desired) Remember to provide proper

support for the bearing and shaft during disassembly.

9.9 Inspection of Bearing when the Machine is Non-O perational

9.9.1 Although roller bearings are robust mechanical components which give long

service, it is however, wise to inspect them now and then. This can preferably be

done during a planned stoppage of the machine or when the machine is to be

dismantled for some reason, such as inspection or repair.

9.9.2 Commence operations by arranging the working area so that it. is as clean and as

dry as possible. Check that replacement bearings are readily available in case they



are needed. If drawings are available they should be studied thoroughly before

maintenance work is begun.

9.9.3 Clean the external surfaces. Note the order in which the machine components are

removed and also their relative positions. Care should be taken not to crack, for

example, labyrinth seals as they are removed. Excessive force should never be used

when removing a seal. Inspect the seals and other components of the arrangement.

9.9.4 Check the lubricant. Impurities of various kinds can usually be felt if a little of the

lubricant is rubbed between the fingers; or a thin layer may be spread on the back of

the hand for inspection against the light.

9.9.5 Ensure that dirt or moisture cannot enter the machine after the covers and seals have

been removed. Cover the machine, exposed bearings and sea-tings with waxed

paper, plastic sheating or similar if work is interrupted.

Do not use cotton waste.

9.9.6 Wesh the exposed bearing where it is possible to carry out inspection wi-thout

dismounting. Use a paint brush dipped in white spirit and dry with a clean lint-free

cloth or compressed air (taking care that no bearing componen start rotating).

However, on no account sealed or shielded bearings be washed.

PAGE 72

A small mirror and a probe, such as dentists use, are useful when inspecting

the raceways,. cage and roll ing elements of the bearing.

If the bearing is undamaged it should be relubricated according to the

instructions provided by the machine manufacturer.

9.10 Bearing Lubrication

All bearings, of whatever type, need to be lubricated

9.10.1 There are four functions a lubricant must perform to ensure that a bearing will give

good service. These are Maintain an unbroken film between metp,@ surfaces.

Prevent excessive friction and the resulting increase in temperature. Conduct heat

away from the bearing's surfaces. Remain stable under severe operating conditions.

Severe operating conditions include temperature, humidity, and vibration.

9.10.2 Proper selection of a lubricant is usually based on four conditions.

These have a direct effect on the lubricant, and they are as follows

Load



Speed

Temperature

Environment

Any one ' or all of the above conditions, may be crucial in an application. Of the

four, the environment of the application is the most variable. This is especially true when

bearings are used outdoors or for processing plant applications where they are subjected to

contact with dust, water, chemicals and other materials. In most cases, the manufacturer

will simply specify that an oil or grease having particular properties or characteristics

should be used.

9.10.3 Oilless bearings, or permanently sealed bearings, should require no attention.

Most plain bearings and rolling contact bearings do,.directly or indirectly. An

example of indirect attention would be the case where a cen-

PAGE 73

tralized and automatic system is used to supply lubricant to the bearing areas. In

that case, you should check the reservoirs to be sure that they are properly filled.

9.10.4 Whether oil or grease should be used for lubricating bearings depends largely on the

equipment design. All that's needed is enough lubricant to keep the bearing surfaces

oiled and slippery.

9.10.5 When oil is used, the most important single factor is its viscosity at the

operating temperature of the bearing. Slow-speed, heavy-duty bearings would

use a heavier oil. Bearings in equipment used outdoors or in buildings which

have no heat will need an oil having a low enough pour point to be sure that

the bearing will run freely when the equipment is started. Bearings used on

equipment located in warm areas will need a heavier lubricant to allow for the

thinning effect of heat on oil.

9.10.6 Greases are chosen for bearing lubrication for low speed applications which don't

generate much heat. As a general rule, grease is used when the running speeds of a

plain bearing aren's above 200 to 300 rpm. One of the particular advantages of

grease in a bearing application is its tendency to stay put. Under normal

circumstances, it won't run out of the bearing as freely as oil does. Grease also acts

as a seal to keep contaminants out.



9.10.7 Applying too much lubricant too often is the most common cause of lubrication

problems with antifriction bearings. Too much oil will cause churning, an- increase

in operating temperatures and result in a lowering of the oil's viscosity. If the oil

gets too thin, it won't carry the load it was intended to and the bearing will fail.

When it does, the equipment it's running in will have to be shut down so that

bearing replacement can be made. The same problem results when an excessive

amount of grease is used.

9.10.8 In practice, you probably will riot often see the bearings you are lubricating. That's

because bearings are usually mounted in a housing or enclosure of some kind. Some

bearings are inside the equipment, and can't be reached easily from the outside.

They're usually lubricated by a system designed for the purpose.

There's a rule of thumb which has been used for a long time : If the bearing housing

is too hot to rest your h-and on, then something's wrong. It's a good rule to follow

and apply.

PAGE 74

9.1 1 Grease Lubrication

9.11.1 Clean housing and grease nipples before injecting fresh grease, if the bearing

housing is not provided with the nipple requisite lubrication should be carried out

during a planned stoppage of the machine.

9.11.2 Remove housing top of end cover. Remove used grease and inspect for any foreign

material, or any other defectwash housing and bearing carefullywith clean solvent

and brush. Do not use cotton waste, use good soft cloth and dry up the. housing,

inspect housing for any visual defects such as cracks or scratches.

9.11.3 Fill the space between the balls or rollers with a grease, which is suitable for the

operating conditions. The free space around the bearing should norma ly be

between a third and half filled with grease. If the bearing is to operate at very high

speed the quantity of the grease in the free space should be just less than one third or

where the bearing is to operate at very slow speeds the free space may be

completely filled with grease.

9.12 Oil Lubrication

9.12.1 Check the oil level and replenish if necessary. Ensure that air vent of the oil level

gauge is not blocked. When the oil is to be changed, it is drained off and the



bearing arrangement raised with fresh clean oil of the same type before refilling

to the required level.

9.12. With the oil bath lubricating change the oil once a year provided the operating

temperature does not exceed 50" C and the oil does not become contaminated.

9.12.3 The oil must be changed more frequently when operating temperatures are higher

than 50'OC, the following guidelines can be useful Fourtime sayear if

temperature is 100"C. Every month if temperature is 120 0 C. Weekly change if

temperature is. 130* C

Note : Use only the oil recommenued by the manufacturer.

PAGE 75

9.1 3 Types of grease

9.13.1 Lubricating grease are oils which contain thickeners, generally in the form of

metallic ; soaps. When selecting a suitable grease it is necessary to consider the

consistency, operating ;temperature range and rust-inhibitilng properties.

'Consistency is classified according to the National Lubricating Grease Institute

(NLG 1) scale. Generally speaking, metallic soap base greases of consist@ntyl,2 or

3 may be used for rolling bearings.

9.13.2 The upper temperature limit for calcium base greases is approximately 6@ C,

calcium base greases containing additions of lead soaps are particularly suitable for

'wet' bearing arrangements, for example, the wire section of a Paper-making

machine. Certain calcium/load base grease provide protection against salt water.

9.13.3 Sodium base greases are available for the temperature range -30c'to -+-8J C and

provide protection against corrosion. They absorb any moisture and form an

emulsion with it.

However, if the amount of moisture absorbed become excessive, the lubricating

properties will 1 deteriorate and there is a risk that the grease will run ou 't of the

arrangement.

9 13.4 Lithium base greases may generally be used at temperatures of -300 C to + 1 10 0 C

and they are resistant to water. If moisture. can enter the bearing arrangement, they

@s@ould therefore contain a rust inhibitor. Lithium base grease with lead

soap additives provide relatively good lubrication even where free water can

penetrate.



A number of different types of high temperature grease are available for

temperatures in excess of 120'C.

However, it is advisable to follow manufacturer's instructions whenever available.

9.14. Lube Oil Selection

9.14.1 Oil lubrication is used for light-to-moderate loads, operating at high rpm. and with

temperatures from 60"to 900 C. Temperatures on either side of this range require oil with

special additives or other types of lubricants.

PAGE 76

If no chart for selecting oil is available, a good rule-of-thumb is to use a

lightweight oil for high speeds and light loads. Heavier oils are used for slow speeds

and heavy loads. Light oil is used for high speed applications because it reduces the

amount of fluid friction between the balls or rollers and the oil. This, in turn, reduces

the operating temperature of the oil.

9.14.2 The viscosities of oils used for lubricating bearings are shown in Fig. 9.5



PAGE 77

Table below shows shaft operating conditions and the oil to be used for each condition. By

comparing this chart with Fig. 9.5 one can see which type of oil should be used for

different temperatures.

9.14.3 When oils are used for low temperature applications, the pour point (lowest

temperature at which the oil is fluid) must be low enough to ensure that the oil

remains in a completely fluid state. If the oil does not have a low pour point,

starting and running friction will be high, increasing wear.

9.14.4 In high temperature application, the oil must be resistant to breaking down and

oxidation. When oxidation occurs, the oil not only loses its effectiveness but forms

deposits that add contaminants to the system.- Most lubricating oils used for ball or

roller bearing applications are formulated with chemical additives to resist oxidation



and improve the viscosity Index of the oil. The viscosity index of an oil is described

as its resistance to change in its thickness with any change in temperature.

PAGE 78

9.15 lubrication Systems

9.15.1 Manual Lubricating Devices

The maintenance craftsman probably uses manual lubrication most of the time when

replacing bearings. The equipment used for manual lubri-. cation can be as simple

as the pump oiler or hand grease gun shown in Fig. 9,6 Some plants have portable

lubrication units consisting of pneumatically or electrically driven pumps mounted

on a truck or handcart. This unit is taken around to the machines requiring

lubrication, saving many steps for the person doing the lubricating. It also

eliminates a//fire or safety hazard by allowing the lubricant to.be@ stored away

from the manufacturing area.

9.15.2 Natural Oil Lubrication Systems

a) Many machines are equipped with gravity or drip-feed lubricating devices.

They consist of a small reservoir mounted above ihe shaft or slideto be

lubricated. A needle or adjusting valve located within the the nousinq

regulates the flow of oil to the equipment, as shown in F ig. 9.7



PAGE 79

b) Another type of natural lubrication frequent y used is called splash or ring lubrication,

shown in Fig. 9.8. Splash lubrication uses the revolving motion of the machine parts

to distribute the lubricant. In splash lubrication, a large gear is partly submerged in

the oil contained in the reservoir or sump. As the gear revolves, it splashes oil around



the housing to lubricate other gears and bearings. In the ring type oiler, a collar or

ring rotates partly submerged in the oil reservoir transferring the lubricant to the

upper part of the shaft.

Oil is scraped from the collar or ring and then flow naturally within the bearing

housing to the points requiring lubrication.

c) Pad and wick oilers are lubricating devices similar in principle to ring and collar

oilers. The pad oiler is simply a small reservoir fitted with a felt pad that is saturated

with lubricating oil. The pad is in contact with the shaft or moving element and

transfers the lubricant from the pad to the

PAGE 80

rotating element gradually. Pad oilers frequently are mounted above the unit with a

wick extending from the oil reservoir to the shaft. The wick transfers the oil from the

reservoir to the shaft. The reservoirs of all the natural lubricating devices must be filled

occasionally to ensure proper lubrication of the rotating or sliding surfaces.

9.15.3 Pressurized Oil lubrication

Recirculating or pressurized lubrication is used for many types of plant equipment,

with many variations in construction. The system shown in Fig. 9,9 has the pump

mounted outside the machine casing, and the oil sump located inside the machine.

In operation, the oil is drawn from the sump, pressurized, and transferred to the

points requiring lubrication. Note that the points being lubricated include not only

the bearings, but the gears also. Different systems include variations, from

mounting the oil pump directly in the sump of a machine-oil sump, to mounting

both the pump and the sump outside the machine in a rerviote location. Whatever

type of device is used, it is importtant that proper lubrication for all contacting or

wearing surfaces is provided.



PAGE 81 10 Trouble Shooting

10.1 Some faults that can be diagnosed by observation are lised in the following table:

SYMPTOM PROBABLEFAULT REMEDY

I) Pump does not deliver liquid

Impeller rotating in wrong direction

Reverse direction of rotation.

Pump not properly primed - Air or vapour lock in suction line.

Stop pump and reprime

Inlet of suction pipe insufficiently submerged.

Ensure adequate supply of liquid

Air leaks in suction line or gland arrangement.

Make good any leaks or repack gland.

Insufficient margin between suction pressure and vapour pressure.

Maintain the correct suction Pressure corresponding to its temperature and pressure.

Discharge head too high Maintain the correct discharge head of the pump as per the manufacture's guidance.

Suction lift too high Keep the suction lift within the permissible ranges. Check with vaccum gauge.

Pump not up to rated speed. Increase speed.



PAGE 82 SYMPTOM PROBABLEFAULT REMEDY

ii) Pump does deliver rated quantity.

Air or vapour Lock in suction line


Inlet of suction pipe insufficiently sub-merged.

Ensure adequte suply of liquid

Pump not up to rated speed. Increase speed


Make good any leaks, or repack gland.

Foot valve or suction strainer choked with debris

Clean head losses in delivery pipes, bends, and valves, reduce losses as required.

Restriction in delivery pipe work, or pipe work incorrect.

clear obstruction or rectify error in pipe work.

Head underestimated Check head losses in delivery pipes, bends, and valves, reduce losses as required.

Unobserved leak in delivery pipe work.

Examine pipe work and repair leak.

Blockage in impeller or casing.

Remove half-casing and clear obstruction

Excessive wear at neck rings.

Dismantle pump and restore clearances to original dimensions.

Impeller damaged. Dismantle pump and renew impeller.




High fluid viscosity Check the recommended viscosity of the fluid for the pump

Pump gaskets leaking. Renew defective gaskets

iii) Pump does not generate rated delivery pressure

Impeller rotating in wrong direction

Reverse direction of rotation.

Pump not up to rated speed.

Increase speed.

Impeller neck rings worn excessively.

Dismantle pump and restore clearances to original dimension.

Impeller damaged.or choked.

Dismantle pump and renew impeller or clear blockage.


iv) Pump loses liquid Suction line not fully primed


--Air or vapour lock in suction line.

Inler of suction pipe insufficiently submerged.

Ensure adequate supply of liquid at suction pipe inlet.


Make good any leaks or renew gland paking.

Liquid seal to gland arrangenent loggin ring (if fitted ) choked.

Clear out liquid seal supply.

Logging ring nor properly located.

Unpack gland and re-locate logging ring under supply orifice.




v) Pump overloads driving unit


Bad leak in delivery line, pump delivering more than its rated quantity.

Repair leak.

Speed too high Reduce speed.

Impeller neck rings worn excessively.

Dismantle pump and restore clearances to original dimensions.

Gland packing too tight. Stop pump, close delivery valve to relieve internal pressure on packing, slacken back the gland nuts and retighten to finger tightness.

Impeller damaged Dismantle pump and renew impeller.

Mechanical tightness at pump internal components.

Dismantle pump, check internal clearances and adjust as necessary.

Pipe work exerting strain on pump.

Disconnect pipe work and realign

Misalllignment of the pump with the driving unit.

Re-check the alignment.

High fluid viscosity Check the recommended viscosity for the pump to be handled.

Shaft bend. Check the shaft bend and should be corrected or if required replace the shaft.




vi) Excessive Vibration Air or vapour Lock in suction line


Inlet of suction pipe insufficiently sub-merged.

Ensure adequate supply of liquid at suction pipe inlet.

Pump and driving unit incorrectly aligned.

Disconnect coupling and realign pump and driving unit.

Worn or loose bearings Dismantle and clear or renew bearings.

Impeller chocked or damaged

Dismantle pump and clear or renew impeller.

Rotating element shaft bent. Dismantle pump and straighten or renew shaft.

Foundation not rigid. Remove pump, strengthen the foundation and re-instal pump

Coupling damaged. Renew coupling


Disconnect pipework and re-align

Operating at very low capacity.

Check tge requirement of minimum flow of the pump.

Foreign material in impeller. Check &b cler it, checking of foot valves is also required to avoid any foreign material ingressing through it.

Unbalanced impeller. Balance the impeller.

Cavitation Check the suction pressure & confirm with the required design pressure. Maintain correct NPSH.




vii) Bearings Overheating

Pump and driving unit out of alingment


Oil level too low or too high.

Replenish with correct grade of oil or dain down to correct level.

Worng grade of oil Drain out bearing, flush through bearings, refill with correct grade of oil.

Dirt in bearings. Dismantle, clean out and flush through bearings, refill with correct grade of oil.

Moisture in oil Drain out bearing, flush through bearings, refill with correct grade of oil.

Bearing too tight. Ensure that bearings are correctly bedded to their journals with the correct amount of oil clearance. Renew bearings if necessary.

Too much grease in bearing.

Clean out old grease with correct grade and amount of grease.


Disconncect pipe work and re-aling.




Not enough bearing cooling (in case of jacket cooling).

Check the jacket cooling media inlet flow and temp.

Oil seals fitted too close by on the shaft.

check the correct fit between the rotating shaft and seal.

viii) Bearings wear rapidly.

Pump and driving unit out of alignemet


Rotating element shaft bent. Dismantel pump,straighten or renew shaft. Renew bearings if necessary.

Dirt in bearings. Ensure that only clean oil is used to replenish bearings. Renew bearings if necessary.

Lack of lubrication. Ensure that oil is maintained at its correct level or that oil system is functioning correctly. Renew bearings if necessary.

Bearing badly installed Ensure that bearings are correctly bedded to their journals with the correct amount of oil clearance. Renew bearings if necessary.

ix) Stuffing box leakage excessive

Wrong grade packing Replace with correct grade of packing.

Improper mounting of packing Follow the correct way to fit the gland packing.




Sleeve wear rapidly. Check the sleeve, if it is badly worn, replace or rectify the sleeve.

Shaft bend. Check the shaft bend, should be corrected or replaced.

Excessive clearances in neck bush

Check the clearances

Sand or dirt in liquid Check the liquid and adopt necessary modification to avoid entering of dirt.

x) Packing with short life.

Wrong grade packing Check and select the correct grade of packings.

Improper installation Follow the correct way to fit the gland packing.

Lack of lubrication. Allow enough lubrication to cool the packing.

Improper placement of lantern ring.

Check the lantern ring hole and casing hole (cooling port) should be in line.

Packing too tight Avoid over tightenign of packings.

PAGE 89

10.2 Check list for Commissioning Of pump after major overhaul

Ensure trial run of motor is completed.,

Ensure fabrication of suction and discharge pipe is completed.

Ensure suction and discharge pipes are supported on permanent hangers.

Ensure all the temporary supports are removed.

Ensure suction and discharge flange bolts are free in the holes.

Ensure alignment is checked.

Ensure suction and discharge pipes are connected after ensuring no foreign material

is inside the pump.

Ensure no change in alignment reading. after pipings are connected.

Ensure in case of any slight change motor, is adjusted.



Ensure in case of considerable change. piping is rectified.

Ensure final alignment is checked and values are within limit of 0.05 mm Ensure

pump bearings are cleaned.

Ensure recommended and required amount oil/grease used.

Ensure pump and motor are coupled.

Ensure coupling bolts are tightened properly.

Ensure rotor is free.

Ensure pressure gauges and thermometers are mounted.

Ensure impulse lines are fabricated.

Ensure any other pipe connection if provided are connected.

PAGE 90

Ensure pump is charged.

Ensure impulse lines are flushed.

Ensure washers are put in union joints.

Ensure pump is rotated number of times when pump is charged.

Ensure coupling guard is fixed and is not touching coupling.

Ensure suitable glands are assembled in case where seals are not recommended.

Ensure the over tightening of glands are avoided.

Ensure cooling water inlet and outlet lines are ready open.

Ensure both the lines are properly flushed.

Ensure inlet and outlet pipes are connected to the pump lines.

Ensure Gaskets are put on union, flange joints.

Ensure cooling water circuit is through.

Ensure no leak in the system.

Ensure pump and motor are cleaned.

Ensure men and material are cleared.

Ensure U.C.B. or Unit incharge is informed about readiness of pump for trial run.

Ensure that enough water (or any fluid which the Pump will handle) is available e.g.

in case of B.F.P. deaerator level should be checked.



Pump Maintenance

Documents

type of pump

pump casing

centrifugal reciprocating

pump remarks

start pump

introduction pump

water water pump volute

lube oil pump