PMP-EN-200

200 Centrifugal Pumps

AbstractThis section describes how centrifugal pumps work, lists their limitations, and explains how to select the right centrifugal pump for a given application. For infor-mation on troubleshooting centrifugal pump problems, see Section 1100. For infor-mation on mechanical seals, or installation or startup of centrifugal pumps, see those sections.

Contents Page

210 Engineering Principles 200-3

211 Fundamentals

212 Head

213 Pump Curves

214 Series and Parallel Operation of Multiple Centrifugal Pumps

215 Effects of Changing Pump Speed (Affinity Law)

216 Effects of Changing Impeller Diameter (Affinity Law)

217 Cut-off Point

218 Specific Speed

219 Effect of Viscosity on Centrifugal Pump Performance

220 Suction Considerations 200-25

221 Pumping Liquids Near Their Boiling Points

222 Cavitation

223 Net Positive Suction Head Available (NPSHA)

224 Required NPSH (NPSHR)

225 Suction-Stealing

226 Horsepower

230 Application and Selection Criteria 200-36April 2009 19992009 Chevron USA Inc. All rights reserved. 200-1

231 Factors in Pump Selection

232 Energy Efficiency for Centrifugal Pumps

200 Centrifugal Pumps Pump Manual233 Special Service Pumps

234 Application Guidelines

240 Centrifugal Pump Descriptions 200-48

250 Mechanical Components 200-77

251 Cases

252 Impellers

253 Wearing Rings

254 Shafts and Shaft Sleeves

255 Throat Bushings and Lantern Rings

256 Glands

257 Balance Drums and Bearings

258 Base Plates

259 Couplings and Coupling Guards

260 Centrifugal Pump Subsystems 200-90

261 Special Requirements for Hot Service

262 Vertical Turbine Pumps

270 Maintaining Centrifugal Pump Flow Rates Close to the Best Efficiency Point (BEP) or Best Efficiency Flow Rate 200-92

271 General

272 Power Measurement

273 Flow Control Methods

274 Proportional Flow Control

275 Self-Contained Flow Control Valves

276 Economics of Flow Control

277 Variable Speed Devices (VSDs)200-2 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal Pumps210 Engineering Principles

211 FundamentalsCentrifugal pumps comprise a wide category of pumps which move liquid by the rotational motion of one or more impellers. Their flow is uniform and normally devoid of pulsations.

A centrifugal pump produces pressure by accelerating a fluid to a high kinetic energy (velocity), then converting that energy to pressure.

Fluid flows into the eye of the impeller and is thrown outward by the vanes of the spinning impeller, slowing as the velocity is converted to pressure in the diffuser or volute. (See Figure 200-1). This momentum exchange provides an increase in pressure or head.

The incoming fluid is pushed into the low pressure area of the impeller eye by higher pressure in the upstream system. Having enough upstream or suction pres-sure to push adequate flow into the pump is a critical design consideration. (Covered in Section 220.)

212 HeadThe term head is used almost exclusively in the centrifugal pumping industry to express pressure. All pump curves are calibrated to read feet of head as a measure of pressure rise. Similarly, suction pressures and, often, friction losses are also expressed as feet of head, not psi.

The concept of head is derived from the fact that a column of liquid will exert a local pressure proportional to the depth of that liquid. For example, the pressure of a column of water increases 0.433 psi for every foot of depth. In other words, at a depth of ten feet, the pressure is 4.33 psi higher than at the surface; at 100 feet, 43.3 psi higher; at 1000 feet, 433 psi higher, etc.

Fig. 200-1 End View of a Centrifugal Pump From Centrifugal Pumps Design and Application by Lobanoff and Ross, Copyright 1985 by Gulf Publishing Company, Houston, TX. Used with permission. All rights reserved.April 2009 19992009 Chevron USA Inc. All rights reserved. 200-3

200 Centrifugal Pumps Pump ManualThe depth, or distance in feet, can therefore be used as a measure of pressure. For water, the equivalent pressures are:

1 foot of head = 0.433 psi (for water at 60F and 1.0 specific gravity) or1 psi = 2.31 feet of head (for water at 60F and 1.0 specific gravity)

Another example of measuring pressure by liquid depth is the barometric pressure, reported as millimeters or inches of mercury.

14.7 psi = 760 mm Hg = 29.92 inches Hg

This relationship illustrates that normal atmospheric pressure (14.7 psi at sea level) is the same pressure that would be exerted at the bottom of a column of liquid mercury 29.92 inches high (assuming zero pressurei.e., a vacuumat the surface of the mercury).

Similarly, visualize a centrifugal pump connected to a vertical pipe on its discharge. The discharge pressure from the pump would push the liquid up the column to a level where the pressure from the height would equal discharge pressure. This height would be the feet of head noted by the pump manufacturer as total head across the pump.

One reason the centrifugal pump industry has settled on head, or feet, as a measure of pressure rise is that a pump will develop the same head regardless of the fluids specific gravity. A pump that develops a column of water (S.G.=1) 1000 feet high will also develop a column of hydrocarbon (S.G.= 0.7) 1000 feet high.

Of course, the actual pressure, in psi, would be quite different between water and hydrocarbon. The pressure developed in a pump and the pressure at the bottom of a column of liquid are both proportional to specific gravity. To convert from feet to psi (and vice versa) use the following equation:

Pressure (psi) = feet S.G. 0.433(Eq. 200-1)

213 Pump CurvesTotal Developed Head (TDH) is a measure of the energy a pump delivers to a fluid. It is equal to the total discharge head minus the total suction head in feet of liquid. The word total is used because each of these heads is composed of the pressure head, velocity head, static head, and head loss. The Total Developed Head is approximated by measuring the discharge pressure and suction pressure at the pump nozzles, subtracting to determine the differential pressure, and converting to units of head in feet. This approximation neglects the velocity head component, which usually results in an error of 1% or less. A centrifugal pumps Total Developed Head depends on the impeller diameter, pump speed, fluid viscosity, impeller and case design, and pump mechanical condition. It also varies with flow rate, largely due to frictional losses in the impeller and casing. This relationship is plotted in a pump curve. These characteristic curves are important to understanding the performance of centrifugal pumps.200-4 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsTypical Characteristic Curves for a Centrifugal PumpMost characteristic curves show the relationship between Total Developed Head (TDH), pump capacity (flow rate), brake horsepower, efficiency, and Net Positive Suction Head Required (NPSHR) for a particular pump. Characteristic curves are also known as head-capacity curves or, simply, pump curves. Two methods are commonly used for plotting the characteristic curves of a centrifugal pump.

Figure 200-2 shows the method used to depict pump performance for a single speed and impeller size. These curves result from a pump test at constant speed. Manufac-turers commonly use these characteristic curves to predict and guarantee pump performance.

Figure 200-3 shows the method used to express more fully the entire range of performance of a pump, with various impeller diameters at constant speed. These curves are commonly used in the selection of a pump for a specific service. The curves in Figure 200-3 are generally made up from the average results of tests for various diameter impellers plotted as shown in Figure 200-2.

Figure 200-4 shows a third method of plotting characteristic curves for a centrifugal pump driven at variable speeds, with a fixed impeller diameter.

Note that practically all performance curves furnished by manufacturers are based on water as the pumped liquid. If the pump is handling some other liquid, adjust-ments must be made for viscosity and specific gravity before flow rate and discharge pressure (psi) can be predicted.

Every centrifugal pump will operate on its characteristic curve if there is enough Net Positive Suction Head Available (NPSHA) for a given S.G. and viscosity. For any given capacity, there will be one total head rise, one efficiency, one horsepower, and one NPSHR.

The slope and shape of the head-capacity curve is affected by individual pump design. Head-capacity curves can take one of four typical shapes, as shown in Figure 200-5.

Steep-rise curve Steady-rise curve Flat curve Drooping curve (will have multiple flow points for a given head)

As a rule of thumb, curves that show a 140% increase in head between the capaci-ties of peak efficiency and shutoff are called steep-rising curves; those showing a 1025% increase are called steady-rising curves; and those with no more than a 5% increase are called flat curves. Rise to shutoff is a function of the following parameters:

Specific speed (Ns) design for the impeller Impeller-outlet-vane angle and volute diffuser area ratio Friction lossesApril 2009 19992009 Chevron USA Inc. All rights reserved. 200-5


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Fig. 200-2 Typical Performance Curve for a 6-inch, Single-stage, Double-suction Centrifugal PumpSpeed and Impeller Diameter Fixed.

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F iameter Variableig. 200-3 Typical Performance Curve for a 6-inch, Single-stage, Double-suction Centrifugal PumpSpeed Fixed, Impeller D


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Fig. 200-4 Typical Performance Curve for a 6-inch, Single-stage, Double-suction Centrifugal PumpSpeed Variable, Impeller Fixed

Pump Manual 200 Centrifugal PumpsPumps with drooping characteristic curves should be avoided because they may exhibit unstable operating characteristics. In some cases, however, such as systems with mostly dynamic loss and no requirements for parallel operation, drooping char-acteristics could be acceptable.

Centrifugal pumps with steady-rise curves are most commonly used. Since the head varies distinctly with a change in capacity, precise flow control can be maintained with this type of curve. The rising curve is a stable curve; for every head, only one corresponding capacity occurs.

System-Head CurvesPlotting the head vs. flow rate in a pumping system can be an aid in system design and pump selection. Such a plot is called the system-head curve.

A system curve represents a complete piping system, i.e., the friction losses of all the piping, elbows, valves, etc., and the total static head vs. flow rate. Each point on the curve shows the head required to deliver that amount of flow through the piping system.

A system-head curve (Figure 200-6) is obtained by combining the system friction curve (Figure 200-7) with a plot of the total developed head. A system friction curve is a plot of friction losses versus flow rate in a piping system.

Superimposing the pump characteristic curve on the system-head curve gives the point at which a particular pump will operate (Figure 200-6, Point A). Changing the resistance of the piping system by partially closing a valve changes the system-head curve. Partially closing a valve in the discharge line produces a second system-head curve, shown in Figure 200-6, shifting the operating point to higher head but lower flow rate. The intersection of the pump characteristic curve and the new system-head curve is the new operating point.

Fig. 200-5 Four Typical Shapes of Head Capacity CurvesApril 2009 19992009 Chevron USA Inc. All rights reserved. 200-9

200 Centrifugal Pumps Pump ManualOperating PointIt is important to understand that a centrifugal pump will operate at one point (assuming the pump curve rises steadily to shutoff). This point is the intersection of the system curve and the pump curve. This is an important concept both for sizing pumps and troubleshooting problems.

This concept also illustrates the most common basis for centrifugal-pump control: discharge throttling. As a control valve in the discharge line varies the total pres-sure drop in the system, the system curve varies. This variance in the system curve causes the operating point to shift right or left on the pump curve, with a resulting increase or decrease in flow rate.

Unstable Head-Capacity (Drooping-Curve) Characteristics Under certain conditions, a portion of the head-capacity curve of a low-specific-speed pump is unstable, causing fluctuations in the pump head, capacity, and power input. Figure 200-8 shows the type of head-capacity curve (a drooping curve) that can cause unstable operation.

In Figure 200-8 the system curves OB, OC, OD, OE and OF correspond to different settings of a pump discharge throttle valve. Point F represents the normal operating condition of the pump. As system resistance is increased (by throttling the discharge valve, for example) the pump is able to supply the additional head until point C is reached on the pump head-capacity curve. Additional system resistance causes the operating point to move into the part of the pump curve where the head decreases as the flow decreases. Operation in this region of the head-capacity curve may result is an unstable surging discharge pressure.

It is not good practice to install drooping-curve centrifugal pumps in parallel. One pump may operate at a lower flow rate than the other and could fail if operating below the manufacturers recommended minimum flow rate.

Fig. 200-6 Pump Characteristic Curve Superimposed on System-Head Curve

Fig. 200-7 System Friction Curve200-10 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal Pumps214 Series and Parallel Operation of Multiple Centrifugal PumpsCentrifugal pumps may be operated in series or in parallel. The combined head-capacity curves for series or parallel operation of two or more centrifugal pumps are obtained as follows:

Series: Add heads for each pump at any given capacity. Parallel: Add capacities for each pump at any given head.

Figure 200-9 illustrates both series and parallel operation for two pumps under various discharge conditions. Two pumps, P-1 and P-2, have head-capacity curves as shown and are to pump through pipe systems with characteristics shown by system curves I, II, III, IV, and V. The intersections of the pipe system characteris-tics with the pump head-capacity characteristics show the quantities and heads at which the pumps will operate either singly, in series, or in parallel. Adequate suction pressure is assumed.

Fig. 200-8 Typical Head-Capacity Curve that May Indicate Unstable Operation (Drooping Curve)April 2009 19992009 Chevron USA Inc. All rights reserved. 200-11


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Fig. 200-9 Typical Series and Parallel Operation of Two Centrifugal Pumps Pumping Through a Pipe System Throttled at the Discharge End

Pump Manual 200 Centrifugal PumpsFigure 200-10 is an example of the difficulty with series pump operation. Two iden-tical pumps, P-5 and P-20, operate in series. The suction and discharge pressures are noted on the diagram. Both pumps should develop the same differential head. Actually, P-5 develops a differential of 20.5 psi and P-20 develops a differential of 72.0 psi. Average capacity is 543 GPM, which is well below the anticipated flow rate. The performance curve for the two pumps, Figure 200-11, shows that P-20 is developing its rated head but P-5 is not. The difficulty is that Pump P-5 is losing suction and cutting off at about 543 GPM as shown on Figure 200-11.

In Figure 200-10, the actual differential developed by P-5 is shown by AC. The differential head developed by P-20 is shown by DG. The sum of these two produced the head required at H for a flow of 543 GPM. If P-5 had been provided with adequate suction pressure, it would have developed a differential head equal to AE. The total pressure which both pumps would have developed is shown by BI.

215 Effects of Changing Pump Speed (Affinity Law)Knowing the effects of varying a centrifugal pumps speed is helpful in many situa-tions, such as adjusting to new service requirements, sizing a new driver, turning down to avoid excessive flow or pressure, etc.

The following affinity law holds for any corresponding points on the head-capacity characteristic curve when the speed is changed:

1. Flow rate (quantity) varies directly with the ratio of change in speed.

2. Head varies with the square of the ratio of change in speed.

3. Horsepower varies with the cube of the ratio of change in speed.

In all three cases, the efficiency remains relatively constant. Efficiency tends to rise very slightly as speed increases, because neither hydraulic nor mechanical losses increase as fast as the square of the speed.

The characteristic curve of Figure 200-4 is marked to show a set of corresponding points for the same impeller at different speeds.

The affinity law for speed change holds with considerable accuracy when speed changes do not exceed a two-to-one ratio and flow is not limited by suction conditions. April 2009 19992009 Chevron USA Inc. All rights reserved. 200-13

200 Centrifugal Pumps Pump ManualFig. 200-10 Analysis of Performance of Two Identical Centrifugal Pumps in Series When Suction Pressure at First Pump is Too Low200-14 19992009 Chevron USA Inc. All rights reserved. April 2009

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Fig. 200-11 The Effect of Abnormal Suction Conditions on Centrifugal Pump Performance

200 Centrifugal Pumps Pump Manual216 Effects of Changing Impeller Diameter (Affinity Law)The curves in Figure 200-3, except the underfiled curve, may be approximated from a single curve by the following rules, which apply to reducing impeller diameter to the stated design minimum without other changes in design. They are applicable to minor changes (5-15%) in impeller diameter.

The following rules may be applied for any corresponding points on the character-istic curves when the impeller diameter is changed:

1. Flow rate (quantity) varies directly with the ratio of change in impeller diam-eter.

2. Head varies with the square of the ratio of change in impeller diameter.

3. Horsepower varies with the cube of the ratio of change in impeller diameter.

These rules are essentially the same as the affinity law for speed change, but do not apply with the same accuracy over as wide a range.

For (1), (2), and (3) all to be true, the efficiency must remain constant for the corre-sponding point. Since this is not exactly what happens, the head calculated by the above rules will be too low. The efficiency will usually drop. The table in Figure 200-12 will aid in estimating how much deviation from the simple rule should be expected. Both columns give impeller diameter, in percent, of original diameter.

When the cut becomes so great that the overlap of the vanes is destroyed, proper guidance or control of the liquid is lost and the performance becomes unpredict-able. When possible, the correct diameter for new conditions should be obtained from the manufacturer.

Conservative practice limits the diameter after cutting to not less than 75% of the full diameter. The pump manufacturer can readily determine the allowable minimum diameter from the impeller drawings.

The affinity law for impeller diameter applies not only to the point of best effi-ciency, but to any corresponding points on the original and calculated new head-capacity characteristics, provided they are not affected by suction conditions.

Fig. 200-12 Impeller Diameters (% of Original)

% to Reduce Impeller, as Calculated by the Affinity Law Actual % Impeller Reduction

65 71

70 75

75 79

80 83

85 87

90 91.5

95 91.5200-16 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsThe combined effects described above are summarized in the affinity law equa-tions shown in Figure 200-13.

Effects of Changing Liquid Specific GravitySpecific gravity (S.G.) has the following effects on pump performance, assuming constant rpm and impeller diameter:

1. Flow rate (quantity) is unchanged by S.G. (although the flow reading on a differential-pressure flow meter varies.)

2. Pressure varies directly with S.G. (Although pressure varies, head is constant.)

3. Horsepower varies directly with S.G.

These relationships are important when converting a pump to another service or if significant changes to fluid gravity are anticipated. For example, converting from a light hydrocarbon service to water service may significantly overload an existing driver.

Increasing the Capacity of a Given PumpIncreasing the capacity and head of a pump within its design limits is usually accomplished by increasing impeller diameter or driver speed.

Small increases can be obtained by underfiling the impeller vanes without changing impeller diameter. This means that the exit end of the vanes are filed back, without cutting the shroud, as shown in Figure 200-14. (Figure 200-3 shows the effect on the pump curve of underfiling the impeller.)

Fig. 200-13 Affinity Law Equations From Centrifugal Pumps Design and Application by Lobanoff and Ross, Copyright 1985 from Gulf Publishing Company, Houston, TX. Used with permission. All rights reserved.

Diameter Change Only Speed Change Only Diameter and Speed ChangeQ2 = Q1 (D2/D1) Q2 = Q1 (N2/N1) Q2 = Q1 (D2/D1 N2/N1)H2 = H1 (D2/D1)2 H2 = H1 (N2/N1)2 H2 = H1 (D2/D1 N2/N1)2

BHP2 = BHP1 (D2/D1)3 BHP2 = BHP1 (N2/N1)3 BHP2 = BHP1 (D2/D1 N2/N1)3where:

Q1 = Initial flow rate

H1 = Initial differential head

N1 = Initial rpm

D1 = Initial diameter

BHP1 = Initial brake horsepower

Q2 = New flow rate

H2 = New differential head

N2 = New rpm

D2 = New diameter

BHP2 = New brake horsepowerApril 2009 19992009 Chevron USA Inc. All rights reserved. 200-17

200 Centrifugal Pumps Pump ManualIn Figure 200-3 the head-capacity curve for the underfiled condition is for the full diameter vanes. Similar effects are obtained by underfiling any other usable diam-eter. Underfiling is adopted only in cases where the standard impeller does not attain the required rating and changing the impeller or using a larger pump is not warranted.

Figure 200-3 shows a set of typical characteristic curves for a 6-inch, single-stage, double-suction pump running at 1770 rpm. Total pumping head, efficiency, and horsepower are plotted against capacity for impeller diameters from 15 to 18 inches using the standard vane, and also for full diameter with underfiled vanes. Note that the underfiled curve is unstable. Underfiling pumps with flat curves can lead to unstable (drooping) curves; this would not happen on pumps with steep curves. This is a good example of why underfiling should be carefully considered.

217 Cut-off PointFigure 200-11 shows that the greatest possible capacity obtainable with this pump is about 1100 GPM, which may be obtained at a head of 150 feet. This point is known as the cut-off point and is the maximum quantity of liquid that the available suction head can force into the impeller. The cut-off point depends on the relationship between required and available NPSH. See Section 220 for a complete discussion of NPSH and Figure 200-21 for an example of NPSH limiting capacity.

Pumps should not be selected with a cut-off close to the required rating. Pumps operating above cutoff will vibrate excessively and fail prematurely.

218 Specific Speed Specific speed is a dimensionless term used to compare the performance and shape of impellers, regardless of their size. Specific speed (usually designated Ns) is the speed, taken in revolutions per minute, at which a geometrically similar impeller would run if it were of such size as to discharge one gallon per minute against one foot of head.

Fig. 200-14 Underfiled Vanes on a Centrifugal Pump Impeller200-18 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsIn practice, specific speed is used to relate the three main parameters (GPM, head, and rpm) to the performance of the pump:

(Eq. 200-2)

where:Q = U.S. gallons per minute

H = Feet per stage

n = Revolutions per minute

Low-specific-speed impellers have high heads and low flow capacities. Impellers for low heads and high flow rates have high specific speeds.

Figure 200-15 gives the general relationships between impeller shape, efficiency, and capacity. It also shows that each impeller design has a specific speed range for which it is best adapted. These ranges are approximate, without clear-cut demarca-tions between them. Most petrochemical pumps are designed with impellers that have specific speeds between 8001500 (as calculated using Equation 200-2).

Ns nQ0.5

H0.75-------------=

Fig. 200-15 Relationship of Impeller Shape, Efficiency, and Capacity From Pump Handbook, (1976) Edited by Karassik, Krutzch, Fraser, & Messina. Used with permission from McGraw Hill.April 2009 19992009 Chevron USA Inc. All rights reserved. 200-19

200 Centrifugal Pumps Pump ManualSpecific speed is a pump design tool, but it may be used in the pump selection process to compare the curve shape and stability. It can also be used in evaluating new pump bids. (See Section 231.)

In general, low specific speeds indicate flat head-capacity curves, with peak effi-ciency over a wide range of capacity, and brake-horsepower decreasing as the pump is throttled. High specific speeds result in steep head-capacity curves, sharply peaked efficiency curves, with brake-horsepower increasing as the pump is throt-tled.

219 Effect of Viscosity on Centrifugal Pump PerformanceSince requirements often call for pumping liquids with a viscosity greater than water (while most manufacturers curves are for pumping water), it is important to have a method for estimating the effect of viscosity upon water performance curves. In general, because of the increased internal fluid friction, the head, efficiency, and flow of centrifugal pumps are reduced when pumping a fluid with a higher viscosity than water.

Figure 200-16 shows the effect of viscosity on pump performance. Figure 200-17 (1 and 2) provides viscosity corrections to pump performance. These data are also available from the Hydraulic Institute Standards, 14th Edition. The curves convert the pumps water performance to that of the viscous fluid.

These correction curves do not apply to mixed-flow or axial-flow pumps, nor to pumps handling non-Newtonian liquids. Slurries and similar non-Newtonian liquids may produce widely different results depending on their characteristics. Also, the correction curves cover only single-stage performance using the best efficiency flow rate for the impeller. If viscous performance for a multi-stage centrifugal pump is required, the head per stage should be used to obtain the proper correction factors, which should then be verified with the original equipment manufacturer.

It is worth noting that, at 100 GPM, Figure 200-17 (1 and 2) gives somewhat different results, indicating they are compiled from separate tests and that either chart is only an approximation of the actual results for a viscous liquid.

The correction curves provide factors to be applied at the best-efficiency-point to arrive at the viscous performance curve. Efficiency is the parameter affected most severely by viscosity, followed by capacity, then head. In practice, since efficiency has the greatest effect, power cost should be evaluated as it may impact the pump selection.

Positive-displacement reciprocating screw or gear pumps are very efficient in viscous fluids. They should be considered when fluid viscosity exceeds 200 to 500 SSU and when there are very few suspended solids present.200-20 19992009 Chevron USA Inc. All rights reserved. April 2009


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Fig. 200-16 Effect of Viscosity on Centrifugal Pump Performance. Note: In Figure 200-17 (both parts 1 and 2, overleaf), enter the chart at GPM, read vertically to on Factor.Head, then Horizontally to Viscosity, then vertically to Head/Capacity/Efficiency, then left to the Correcti

200 Centrifugal Pumps Pump ManualFig. 200-17 Viscosity Corrections for Centrifugal Pumps Handling Viscous Fluids 100 GPM and Over (1 of 2) From Standards 14th edition, Hydraulic Institute. Used with permission.200-22 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsFig. 200-18 Viscosity Corrections for Centrifugal Pumps Handling Viscous Fluids Under 100 GPM (2 of 2) From Stan-dards 14th edition, Hydraulic Institute. Used with permissionApril 2009 19992009 Chevron USA Inc. All rights reserved. 200-23

200 Centrifugal Pumps Pump ManualSample Problem: Viscosity Effects. Given the pump performance obtained by test on water, plot the performance of this pump when handling oil with a specific gravity of 0.9 and a viscosity of 1,000 SSU, both at pumping temperature.

On the performance curve, Figure 200-16, the best-efficiency-point when pumping water is 750 GPM at 100 ft of head (Point A) with an efficiency of 82% (Point B).

Using 750 GPM, 100-ft head, and 1,000 SSU, read Figure 200-17 (1 of 2) and deter-mine the correction factors:

Multiplying the water capacity, head, and efficiency by the correction factors gives the best-efficiency-point as follows:

Viscous capacity:

750 GPM 0.95 = 712 GPMViscous head:

100 ft 0.92 = 92 ftViscous efficiency:

82% 0.635 = 52%The point for viscous capacity and head can now be located below the water curve (Point C, Figure 200-16). The viscous head-capacity performance curve is drawn from the water head at zero capacity (Point D) through the viscous head-capacity point (Point C) with approximately the same shape as the water curve. The effi-ciency at the best-efficiency-point for viscous performance can be plotted as Point E and the viscous efficiency curve plotted from zero (Point F) through Point E; the shape of the curve is similar to that obtained for water efficiency.

The horsepower (BHP) for any capacity can now be calculated from the head and efficiency at the capacity desired. The best-efficiency-point for viscous perfor-mance is:

(Eq. 200-3)

This horsepower can now be plotted as Point G and the horsepower curve for viscous performance drawn through Point G approximately parallel to the brake horsepower curve for water.

Capacity correction factor: CQ = 0.95Head correction factor: CH = 0.92Efficiency correction factor: CE = 0.635

BHP 712GPM 92 ft. 0.9 S.G.3960 0.52 eff-------------------------------------------------------------------- 28.6= =200-24 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal Pumps220 Suction ConsiderationsOne of the most important aspects of successful pump operation is to have enough suction pressure to push liquid into the pump without flashing or boiling. This requirement is particularly critical where liquids are already near their boiling points (reflux, boiler feedwater, flash separators, furnace circulation, etc.). Failure to assure adequate suction pressure will lead to numerous operational and mechanical problems, up to and including destruction of the pump.

221 Pumping Liquids Near Their Boiling PointsPumps should be selected with inlet velocities sufficiently low to prevent vapor formation in the entering liquid. This may call for (1) oversized inlet piping, (2) pumps operating at low speed, (3) pumps designed for such conditions, or (4) use of vertical pumps installed in a suction can.

The design requirement is that the pressure at the pump inlet be adequate to accel-erate the liquid to the required velocity at the impeller entrance without the pressure in the pump falling below the fluids vapor pressure. Boiling or flashing of the fluid in the pump suction eye is called cavitation and can significantly affect pump performance.

222 CavitationThe formation of vapor bubbles in the impeller suction eye due to fluid flashing or boiling, with subsequent collapse of the bubbles as the pressure rises, is called cavi-tation. Cavitation may cause vibration, pitting damage, and impaired performance. Cavitation may or may not be serious depending on the pump, HP/stage, impeller design, and the fluid being pumped. In small pumps with low differential head per stage, the energy of collapsing bubbles is much less than in larger, high-head-per-stage pumps. Cavitation is more severe in a single-boiling point fluid (like water) than with a mixture (like petroleum stocks) that have a broad boiling range.

RecirculationRecirculation is a flow reversal at the inlet eye or discharge tip of an impeller. Recirculation at the inlet eye is called suction recirculation. Discharge recirculation occurs at the impeller tip. Recirculation usually occurs when operating centrifugal pumps at flows below their best efficiency flow.

Refer to standard drawing GA-G1097-2, Minimum Continuous Flow for Centrif-ugal Pumps, to help predict the flow at which a pump will begin to demonstrate problems related to suction recirculation. Section 270 describes several ways to prevent pump operation below the recommended minimum flow.

All impellers will begin to recirculate at a certain flow rate. The point recirculation begins may not be the same for suction and discharge. Suction recirculation usually will begin at a higher flow than discharge recirculation.April 2009 19992009 Chevron USA Inc. All rights reserved. 200-25

200 Centrifugal Pumps Pump ManualThe capacity at which recirculation occurs is determined primarily by the impeller design. Most of the problems associated with recirculation can be avoided by selecting pumps with impellers of low suction specific speed (Nss) designs. Recom-mended limits for Nss are:

The effects of recirculation can be impeller and casing damage, bearing failures, and seal or shaft failures. Symptoms associated with recirculation are listed below.

Suction Recirculation: Cavitation damage to the pressure side of the impeller vanes at the inlet of

the vane.

Cavitation damage to the stationary or splitter vanes in the suction side of the pump casing.

Random crackling or gravel pumping noise. (Inadequate NPSH will sound the same except the noise will be constant not random.)

Surging pressure in the suction pipe.

Discharge Recirculation: Cavitation damage to the pressure side of the impeller vane and exit shroud at

the discharge of the impeller. This may be seen as impeller failures at the impeller exit vanes or shroud.

Higher-than-normal axial vibration or shaft movement. This may be accompa-nied by thrust bearing damage.

Cavitation damage to the cut water (casing tongue) or diffuser vanes in the case.

223 Net Positive Suction Head Available (NPSHA)NPSHA is a critical factor in pump performance. It is a result of the suction system design. In practical terms, NPSHA is the differential pressure between (1) the actual pressure at the lowest pressure point in the pump, and (2) the pressure at which the liquid begins to vaporize (flash or boil). NPSHA is the available pressure above the liquids vapor pressure that prevents vaporization (or cavitation). Remember that as the liquid accelerates into the spinning impeller eye, its pressure drops. If the pressure falls below the vapor pressure, cavitation occurs.

NPSHA is technically defined as the total suction pressure (in psia) at the suction nozzle less the true vapor pressure of the liquid (in psia) at the pumping temperature. For centrifugal pumps, NPSHA is always expressed in feet of the liquid pumped.

Horsepower Per Stage < 250 to 300 > 300

Nss limit 11,000 9,000200-26 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsNet Positive Suction Head Required (NPSHR)NPSHA must exceed the NPSH required by the pump. NPSHR depends on the impeller design, operating speed and flow rate, and, to a lesser extent, on the charac-teristics of the liquid handled. NPSHR represents the frictional losses and initial pressure-to-velocity energy conversions occurring between the suction flange and the point where the impeller begins to do work on the fluid.

During NPSH testing and NPSH curve development, the pump manufacturer oper-ates the pump at a constant flow rate while closely monitoring the pump head as suction pressure is reduced. During the process of lowering suction pressure, cavita-tion begins. When the volume of the vapor bubbles impairs pump performance by a reduction in head of 3%, the pump manufacturer defines that NPSH value as the required NPSH for that particular flow. This is repeated at several flow points to develop an NPSHR curve.

NPSH testing is done using cold water as the pumped fluid. The values of NPSHR determined from cold water tests are conservative and are practical to use for virtu-ally all services.

NPSHR, Suction Specific Speed, and Minimum FlowThe NPSHR by a pump is largely dependent on the impeller eye area and inlet vane angle design. These relatively complicated and proprietary design features can easily be evaluated by comparing each pumps Suction Specific Speed (Nss).

Nss is a design number which relates the best-efficiency flow and NPSHR for the maximum diameter and pump rpm. This value provides a great deal of information about pump performance. To calculate Nss, use the following formula:

(Eq. 200-4)

where:Q = pump best efficiency flow in GPM for the maximum diameter

impeller. Q divided by 2 is used for double suction impellers.

N = pump rotating speed in rpm

NPSHR = net positive suction head required in feet at flow point Q

Typical values for Nss range between 7,000 and 14,000 as determined by pump design. However, conservative impeller designs will have a Nss value less than 11,000. Multistage, high-energy pumps which operate above 3600 rpm should have a first-stage impeller Nss value of less than 9000.

Nss Q 0.5N

NPSHR 0.75----------------------------------=April 2009 19992009 Chevron USA Inc. All rights reserved. 200-27

200 Centrifugal Pumps Pump ManualThe following is an example of the relationship between Nss, NPSHR, and pump minimum flow.

Pump #1 with the lower Nss requires a higher NPSHR and has a lower minimum flow. Therefore: (1) Pump #2 probably has a larger impeller inlet eye area and less conservative inlet vane angle design; and (2) due to the less conservative design of Pump #2, the stability of flow in the impeller is reduced at lower flow rates resulting in a higher minimum flow.

In summary, as Nss increases, the pump NPSHR decreases, and the pump minimum flow increases.

Company experience has shown that pump reliability is directly related to the pump Nss. Pumps with Nss values above 11,000 are less reliable. The lower reliability usually manifests itself as high vibration and shaft deflection due to flow instability in the impeller eye. The shaft deflection and vibration results in reduced mechan-ical seal and bearing life.

Refer to Figure 200-19 for a nomograph to help determine NPSHR or Nss values for pumps without the need for calculation. The nomograph along with basic knowl-edge of pump performance requirements can (1) assist in the selection of a conser-vatively designed pump by establishing design parameters for new or retrofit of existing pump suction systems; and (2) help diagnose problems with existing pump suction systems.

Refer to GA-G1097-2 to help determine the stable operating range for the selected pump based on its Nss. This figure can also be used to compare minimum flow quotes from various vendors, as they often will not consider the Nss of the pump when quoting the stable minimum flow.

PUMP #1 PUMP #2

Manufacturer ABC Co. XYZ Co.

Model 3 2 8 3 2 8Speed (rpm) 3,600 3,600

NPSHR (feet) 10 6

Nss 8,750 11,500

Minimum flow (GPM) 30 60200-28 19992009 Chevron USA Inc. All rights reserved. April 2009

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Fig. 200-19 Specific Speed and Suction Specific Speed

200 Centrifugal Pumps Pump ManualNPSHR for Liquids Other than Cold WaterManufacturers test data for NPSHR are published based on cold water and are normally included on pump performance curves. When liquids other than cold water are handled, the actual NPSHR becomes uncertain. Tests, however, indi-cate that cavitation starts at nearly the same NPSH for all liquids, but that some liquids (primarily high-vapor-pressure liquids such as propane and butane) do not require as much NPSH as does cold water.

Three factors cause the NPSHR for some liquids to be less than for cold water:

1. Vaporization removes heat from surrounding liquid, reducing its vapor pres-sure, and suppressing further vaporization. The magnitude of this effect depends on the thermodynamic properties of the liquid at the suction condi-tions.

2. The volume of vapor bubbles in the impeller eye determines the extent to which performance is impaired. The volume of vapor formed depends on the pressure and temperature at which vaporization takes place and on the molecular weight of the stock. To make the same volume of vapor, more weight of a high-vapor-pressure stock must be vaporized than of a low-vapor-pressure stock. The higher molecular weights of hydrocarbons compared to water require more hydrocarbon than water to be vaporized for the same volume of vapor formed.

3. Multi-component liquids have light ends that vaporize first. These may be small enough in proportion to the total fluid so that some vaporization can reduce the vapor pressure before pump performance is seriously impaired. This effect will vary with changes in the composition of the hydrocarbon. Some hydrocarbons require almost as much NPSH as cold water if the fractions of the stock first evaporating are significant in relation to the whole NPSH for a given service condition. The use of any NPSH correction factor which supposedly allows less NPSHR than cold water is not recommended.

Vapor Pressure and NPSHA primary factor in calculating the NPSHA for a pump is the vapor pressure of the liquid handled. One commonly used method, Reid vapor pressure, requires a certain amount of liquid to be evaporated in the measuring apparatus before the vapor pres-sure is indicated. Such vapor pressures are too low for determining when gas evolu-tion will start (the point that will affect pump performance). This error is variable, being small for fractioned stocks and greater for wild crudes. The true vapor pres-sure (TVP) at the pumping temperature should be used for NPSHA calcula-tions rather than vapor pressure by the Reid method.

In determining true vapor pressure, do not overlook the possibility of dissolved gases in the liquid. A frequent cause of NPSH trouble is dissolved or entrained air or gas in the liquid pumped. When tested by the bubble-point method, water which has been aerated has a higher vapor pressure than water which has not been aerated. The same is true for hydrocarbons or other liquids. When the pressure of a liquid containing dissolved gases is reduced, the gas dissolved in the liquid may evolve and cause an effect similar to cavitation.200-30 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsYou must consider the effect of temperature changes on vapor pressure in determining the NPSH available for a pump. Vapor pressure is a function of temperature alone for any given composition of liquid. For some fluids, a small increase in temperature causes a relatively large increase in vapor pressure. When selecting a pump for such a fluid (water, for example), see that the NPSHA is calcu-lated at the highest probable fluid temperature.

The same precaution applies to pressure changes. The NPSHA must take into account any reduction in suction pressure that might result from pressure variations in the system. This is of particular importance in applications such as boiler feed pumps, where you should always make reasonable allowance for variation in deaer-ator pressure and its effect on pump suction.

NPSHR QuotationsSince most pumps are tested by the manufacturer on cold water only, quotations by the supplier will usually provide the cold water NPSHR.

Calculation of NPSHA NPSHA can be calculated as follows:

NPSHA = H + S - F - Vp(Eq. 200-5)

where:NPSHA = feet of head of the pumped liquid, at the pump impeller-eye eleva-

tion and suction flange face.

H = minimum absolute pressure on the surface of liquid pumped, in feet of the liquid.

S = static head, or vertical distance between the surface of the liquid and the center of the impeller, in feet. S is negative (-) when the pump is above liquid surface, and positive (+) when the pump is below.

F = friction losses, in the suction pipe and fittings, in feet of the liquid.

Vp = True vapor pressure of the liquid, in feet of liquid, at pumping temperature. For water this may be determined from the steam tables. For hydrocarbons refer to ETC technical data books, process designs, or other sources. (Also see the Appendix.)

H and Vp are calculated from pressures in absolute, not gage units. (Absolute pressure = gage pressure plus atmospheric pressure).

Sample Calculation: Static Head (S)Gasoline is to be pumped at a rate of 300 GPM from a tank having atmospheric pressure on the surface of the gasoline. What is the minimum required static head, S, to satisfy the pump NPSH requirements?April 2009 19992009 Chevron USA Inc. All rights reserved. 200-31

200 Centrifugal Pumps Pump ManualSince we want to obtain Static head (S), Equation 200-5 can be rearranged to:

S = Vp + F + NPSHA - H

A check on the gasoline shows that the true vapor pressure is 10 psi absolute, and the specific gravity is 0.75. Therefore:

Vp psia (2.31 feet/0.75) = 30.8 ft.From the size and length of the line, fittings, and quantity to be pumped, the friction head loss of the suction line is found to be:

F = 10 ft.

To calculate NPSHA for the specified pump flow of 300 GPM, Figure 200-19 shows the pump requires a NPSH of 10 feet, assuming 3600 rpm operation and a Nss of 11,000.

Since the objective is to find the necessary static head (S) to satisfy the pump NPSH requirements, we can substitute the 10 feet required from Figure 200-19 and add an operating margin of 4 feet, for the minimum necessary NPSHA.

In other words, we must provide:

(The minimum recommended operational margin is 2 feet, a margin of 4 feet is preferred.)

H is the atmospheric pressure, or 14.7 psia:

14.7 (2.31/.75) = 45.4 feet of gasolineSubstituting in the equation,

S = Vp + F + NPSHA - H

S = 30.8 + 10 + 14 - 45.4

and

S = 9.4 ft.

The positive value of S indicates that the center of the impeller must be below the surface of the gasoline; the example shows that the center of the impeller should be at least 9.4 feet below the lowest level of the gasoline in the tank.

Figure 200-20 shows variations of the equation for calculating NPSHA, depending on whether the liquid surface is above or below the pump centerline, and open or closed to atmospheric pressure.

NPSHR from Figure 200-19 10 feetOperational margin 4 feetSystem NPSHA by design 14 feet200-32 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal Pumps224 Required NPSH (NPSHR)NPSHR is a function of pump design, varying with the capacity and speed of any given pump. While NPSHA is easily calculated for a given set of conditions, the NPSHR for a particular pump must be obtained from the manufacturer (determined by the actual testing of a similar pump) or estimated from Figure 200-19.

Fig. 200-20 Calculations of System Net Positive Suction Head Available (NPSHA) for Typical Suction Conditions Cour-tesy of Goulds Pumps, Inc.

Legend:

S = Static head, feet absolute

Vp = Vapor pressure of the liquid at maximum pumping temperature, in feet absolute

H = Pressure on surface of liquid in feet absolute

F = Friction losses, feet absoluteApril 2009 19992009 Chevron USA Inc. All rights reserved. 200-33

200 Centrifugal Pumps Pump ManualIf NPSHR is particularly critical for the pump application being considered, an NPSH test can be specified for the actual pump being furnished. This test is recom-mended if the difference between NPSHR and NPSHA is less that 4 feet for a centrifugal pump.

For a properly designed pumping system:

NPSHA NPSHR + OM(Eq. 200-6)

where OM (operating margin) is the extra margin to suppress cavitation.

Values of OM may be selected from experience or in consultation with a specialist. For most centrifugal pump applications, a 2-foot margin should be considered as a minimum, with values from 3 to 5 being recommended. Any margins less than 4 feet should be demonstrated by an NPSH test in the manufacturers shop. New pump or impeller designs should also be NPSH and performance tested.

Limit of Capacity Due to NPSHFigure 200-21 shows a method for computing the capacity limitation imposed by the NPSH on a given pump.

225 Suction-StealingWhen two or more pumps are connected to the same suction header and operated in parallel, the total volume pumped is often much less than proportional to the num-ber of pumps used. One pump seems to take all the liquid from the other pump or pumps. This effect, called suction-stealing, arises from unequal suction pressures at the impeller inlets of the various pumps. It is most pronounced where the pres-sure in the suction header is low, so that the inequalities in friction between the inlet to the header and inlets to the various pump impellers greatly influence the volume of flow into the pump. The remedy is to provide equal head losses between the inlet to the header and the inlets to the pump suction nozzles and adequate NPSHA to both pumps at the total flow rate. Independently matched pump curves give the same effect, especially if they are flat, permitting minor inlet piping variances to produce major effects. Actual cases of suction-stealing can usually be traced to flat or unstable curves.

It is equally important that pumps in series have adequate suction pressure. Occa-sionally, pumps in series operation have not developed the anticipated total differen-tial head. This is usually the result of one pump operating under cavitating conditions because of insufficient NPSHA. Figure 200-21 shows how capacity is limited when adequate NPSHA is not provided.200-34 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal Pumps226 HorsepowerThe hydraulic horsepower (HHP) for a centrifugal pump is a theoretical value calcu-lated from the rated capacity and differential head, assuming a 100% efficient pump. It can be calculated as:

HHP = ( Q H S.G. ) / 3960where:

HHP = hydraulic horsepower

Q = rated capacity in gpm

H = differential head at rated capacity in feet

S.G. = fluid specific gravity(Eq. 200-7)

Fig. 200-21 Limit of Capacity Due to Net Positive Suction Head (NPSH)April 2009 19992009 Chevron USA Inc. All rights reserved. 200-35

200 Centrifugal Pumps Pump ManualOnce the pump efficiency is known, the rated power (BHP) can be determined. The rated power is the power which the pump driver must transmit to the pump shaft at the rated pump capacity. It can be calculated as:

BHP = HHP / effwhere:

BHP = rated power in horsepower

HHP = hydraulic horsepower

eff = pump efficiency at rated capacity as a fraction

(Eq. 200-8)

Pump efficiency is determined empirically from the pumps factory performance test, and appears on the pumps characteristic curve.

230 Application and Selection CriteriaThis section discusses the criteria for selecting a centrifugal pump for a specific service. It is assumed that a centrifugal pump has been selected rather than a posi-tive displacement pump. This material provides background information on selecting a pump configuration for most applications in the petrochemical industry.

While this section provides general information for pump selection, engineering judgement and user preferences must always be considered in the final decision. Keep in mind that you are trying to minimize the sum of first cost, operating cost, and maintenance cost for every selection. Also note the potential flexibility required in operations and changes in environmental laws (which might require multiple seals where a pump cannot accommodate it).

231 Factors in Pump SelectionGeneral Pump QualityRecommended practice is to specify that any pump in heavy-duty or critical service be manufactured to API Standard 610. This includes all continuous-duty, process-plant, hydrocarbon pumps and all other pumps in critical services (i.e., boiler feed-water, off-plot charge pumps, high-pressure waterflood, etc.). Light duty pumps (smaller than 150 HP and in noncritical services) are often purchased to meet ANSI Standards or as general purpose pumps to supplier standards.

In practice, most pumping needs are met with single-suction, single-stage, 3600/1800 rpm centrifugal pumps. These are the work horses of the industry and are generally the best choice for a given service. Historically, these have been hori-zontal pumps. In recent years, however, single-stage, vertical, in-line pumps have often proven to be as reliable and usually less expensive to purchase and install.

In all cases, the user should be consulted on proposed selections. There may be local preferences based on past performance. Availability of maintenance and stocking of interchangeable parts can also be significant factors.200-36 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsANSI versus APIThere are significant construction and design differences between ANSI and API pumps. These differences will impact the pump selection. A tabulation of major differences is shown in Figure 200-22.

There are two major differences: pressure rating and materials of construction. ANSI pumps are limited to 150# ratings. Also, ANSI pumps are not readily avail-able with carbon steel casings or impellers. Cast iron or ductile iron are ANSI stan-dard materials.

There are two limitations with use of cast or ductile iron.

Cast or ductile iron castings (case and impeller) cannot be repaired by welding.

Cast iron materials are susceptible to cracking due to thermal shock. When a hot cast iron pump is exposed to cold extinguishing fluids it may crack. If the pump was pumping a flammable or hazardous fluid, it could feed a fire or cause other environmental hazards.

If ANSI pumps meet the required service conditions but cast or ductile iron mate-rials are not acceptable, consider using 316 SS.

Fig. 200-22 Comparison of ANSI and API Pump Designs (1 of 2)

ANSI APIType Pump and Specification

ANSI B73.1 for horizontal end suction top discharge pumps. ANSI B73.2 for vertical in-line pumps. All are single stage.

API 610 for horizontal single and multistage pumps, vertical in-line, vertical single and multistage centrif-ugal pumps.

Maximum Allowable Working Pressure (MAWP)

275 PSIG Minimum 700 PSIG Some API pumps are designed for pressures above 5000 PSIG.

Hydrostatic Test Pressure

415 PSIG Minimum 1050 PSIGAPI pump hydrostatic test pressure will be 1.5 times the MAWP.

Flange Rating 150# flat faced is standard. 150# raised face is available.

300# raised face is standard. 600, 900, 1500, and higher ratings are available if required by the service.

Maximum Temperature 250F Pump casing is foot mounted which limits allow-able thermal growth.

800F Pump casing is centerline mounted. No casing thermal growth limitations.

Materials of Construction (Casing and impeller)

Ductile Iron 316 SS Alloy 20 A carbon steel casing or impeller is not commonly available.

Carbon steel casing is standard; stainless steel is also available. Impeller materials are cast iron, carbon steel, and stainless steel.

Maximum Head Differential

550 to 600 feet ANSI pumps are only single stage. Maximum impeller diameter is about 13 inches.

Practical limit is 10,000 feet. Horizontal API pumps can have as many as 14 stages.

Impelller Design and Attachment

Open impellers are common. Some enclosed impellers are available. No standard for attachment to the shaft. Most are threaded on the end of the shaft.

All are enclosed design. Some open designs are avail-able for special coke crushing services. Impellers must be key driven with a lock nut attachment.April 2009 19992009 Chevron USA Inc. All rights reserved. 200-37

200 Centrifugal Pumps Pump ManualHead/Capacity ConsiderationsThe head-capacity requirement is a significant factor in selecting pumps. Proper definition of these parameters requires considerable thought to be sure all possible operating conditions have been considered. This is discussed in detail in Section 130, System Hydraulic Design.

The performance of centrifugal pumps over a range of Heads and Capacities is a function of the pump impeller and case design. There are three general impeller designs: radial-flow, mixed-flow, and axial-flow (or propeller). These designs and their relative performance are noted in Section 210, Engineering Principles.

Figure 200-15 indicates the general shape of the characteristic curves for radial, mixed flow, and axial (propeller) pumps. It shows the head, brake horsepower, and efficiency plotted as a percent of their values at the design, or best efficiency, point of the pump.

The head curve for a radial flow pump is relatively flat, and the head decreases gradually as the flow increases. Note that the brake horsepower increases gradually over the flow range with the maximum normally at the point of maximum flow.

Mixed flow centrifugal pumps and axial flow or propeller pumps have considerably different characteristics. The head curve for a mixed flow pump is steeper than for a radial flow pump. The shut-off head is usually 150% to 200% of the design head. The brake horsepower remains fairly constant over the flow range. For a typical axial flow pump the head and brake horsepower both increase drastically near shut-off.

The distinction between the above three classes is not absolute, and there are many pumps with characteristics falling somewhere between the three.

Head-capacity ranges, and other pump features are shown in the Application Guidelines (Figures 200-23 and 200-24) and on the Pump Description sheets in Section 240.

Standard Dimensions ANSI pumps are built for interchangeability between manufacturers.

No standard dimensions apply.

Shaft Sleeves Not required but are available. Fit to the shaft and extension past the gland are not ANSI spec-ification requirements.

Are required to prevent shaft damage in the seal or packing area. Sleeve and stuffing box design is part of the API 610 specification.

Lubrication Can be grease or oil lubricated. Oil lubrication is required. Usually ring oil system is provided.

Thrust Bearing and Life Antifriction bearings only. B-10 bearing life of 17,500 hours at design load is required.

Antifriction ball bearings must be duplex, single-row, 40-degree angular-contact type, installed back to back. L-10 bearing life must exceed 25,000 hours at rated conditions, or 16,000 hours at maximum axial and radial loads at rated speed.

Wear Rings Not required and not available in most designs due to the use of open impellers.

Case and impeller, front and back wear rings are required. Wear ring clearances, attachment, and hard-ness differential are specified.

Fig. 200-22 Comparison of ANSI and API Pump Designs (2 of 2)200-38 19992009 Chevron USA Inc. All rights reserved. April 2009

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Fig. 200-23 Horizontal Centrifugal Pump Application Guidelines


Pump Manual

200-40


Fig. 200-24 Vertical Centrifugal Pump Application Guidelines

Pump Manual 200 Centrifugal PumpsAlthough 3600/1800 rpm, single-stage pumps are the most popular selections in the centrifugal pump family, the following factors may preclude their use.

High HeadWhen an installation calls for a high head combined with a low-flow rate (outside the typical range of single-stage pumps), a high-speed, single-stage, vertical-in-line pump should be investigated. If requirements exceed the limits provided by this pump, a multi-stage centrifugal or positive displacement pump may be suitable.

Axially-split, horizontal, multi-stage pumps should be limited to approximately 2000 psig discharge pressure. Higher heads require double case or barrel pumps, which are inherently more expensive. In special cases such as high-pressure pipe-lines with limited NPSH available, pumps in series may be considered, but shaft sealing becomes increasingly difficult as pump inlet pressures increase.

Some situations require vendors to develop a design for a particular service. For example, the feed pumps in the Richmond Refinery ISOMAX TKN units were designed to pump 1425 GPM of light hydrocarbons against an 8900 ft head at 300F. These pumps are radially-split, horizontal, 14-stage, 6600 rpm, and stretch the vendors experience in design and operation for proven machinery. However, prototype pumps are definitely not recommended. Consult a specialist in such situations and always check the users list carefully when in doubt.

Low Head/High FlowIf a requirement calls for low head (50-200 ft) combined with a high pumping rate (greater than 5000 GPM) that does not fall within the parameter range provided by horizontal or in-line pumps, high-capacity pumps should be investigated.

There are also many double-suction pumps available that provide higher heads than mixed-flow or axial-flow pumps. These are designed to move large quantities of liquid without the usual high NPSH required by high-capacity suction pumps. Typical services include transfer and loading pumps, ballast pumps, and cooling water pumps.

Another pump type for very low heads in water service is the Archimedes Screw Pump. The Company has almost no experience with these.

Physical InstallationIn some cases, the physical arrangement of the installation is a significant factor in pump selection. This is especially true when adding to existing facilities or retrofit-ting a plant. For example, there may be limited space available, resulting in the installation of a vertical, multi-stage, barrel pump where a horizontal pump with fewer stages would be the first choice. This is also true for offshore platforms where deck space is at a premium.

NPSHSuction considerations often dictate pump selection. Cavitation can be of prime concern if there is limited NPSH available or if suction lift is required. Pumps which operate at low speed, have high Nss (suction specific speed), or have double suction April 2009 19992009 Chevron USA Inc. All rights reserved. 200-41

200 Centrifugal Pumps Pump Manualimpellers require less NPSH. In certain cases, vertical-turbine barrel or self-priming pumps may be the most reasonable solution. Vertical sump pumps can be used when suction lift is required, if the head requirement is not too high.

Operating TemperatureMost pump installations operate at 250F or less, and pump design temperature is normally not a problem. In high temperature situations (greater than 450F), atten-tion must be given to pump materials and mechanical design, as they relate to the stock and severity of service. Auxiliary cooling of bearings and seals is recom-mended in most pumps starting at 300F, plus pedestal cooling at temperatures above 500F. Some process pumps operate above 800F. Suggested bearing, seal, and pedestal cooling arrangements are shown in API-610.

Three special design features needed for hot service:

1. An arrangement that permits piping and pump thermal expansion without moving bearings out of line or imposing undue loads on them.

2. Corrosion-resistant materials suitable for the pumping temperature.

3. A design that minimizes leakage and confines it to avoid ignition and hazard to personnel. Mechanical seals are used in almost all centrifugal pump services. See Section 800, Mechanical Seals.

Hazardous StocksSpecial care must be given to installations handling toxic or hazardous stocks (H2S, LPG, Ammonia, chlorine, HF, other acids, etc.) or hydrocarbons above their flash point. In such cases, pumps that can take dual mechanical seals, or seals with external flush should be considered. Pump materials must be carefully selected for compatibility with toxic, hazardous, or corrosive stocks. Suggested seal flush arrangements are also shown in API 610 and Section 800. Canned seal-less, and hydraulic-seal pumps are available for low head/low HP applications. See Section 150 for H2S considerations.

Dirty FluidsDepending on the pumped fluid and its contaminants, some pumps will require more frequent maintenance than others. This can be due to entrained solids (as in crude oils, FCC cycle oils, sandy water, sludges, etc.) or the corrosivity of the fluid itself.

Pumps with replaceable liners in the pump case are also available. Centrifugal pumps in abrasive service should operate near the best-efficiency point to avoid imbalanced hydraulic forces that accelerate wear.

When selecting pumps for such service, consider access to bearings and seals and the pump itself. In such cases, consider pumps that can be disassembled without disturbing connected piping (back pull-out feature), or that allow seal replacement in place (cartridge seals).200-42 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal Pumps

Intermittent OperationCentrifugal pumps are normally designed for continuous operation. If frequent shut-downs are possible, the pump should remain flooded. If this is not possible, or suction lift is needed, the seals must be flushed at startup. Canned pumps with stock-lubricated bearings and pumps with close internal clearances must never be run dry. Intermittent operation is generally harder on a pump than continuous operation.

232 Energy Efficiency for Centrifugal PumpsOperating costs account for a major portion of the total cost of ownership of pumps. Small increases in efficiency (12%) can result in company-wide energy savings amounting to several million dollars per year. Selection of the proper impeller size and the proper number of stages can significantly affect pump efficiency. For all centrifugal pumps, wear ring design, materials, and running clearances may improve efficiency.

Impeller ConsiderationsImpeller disc friction is a major factor affecting overall efficiency. The outer surfaces of a rotating impeller are subject to friction with the surrounding fluid. Some of this friction is recovered as contribution to pump head if the rotating flow induced by disk friction freely enters the pump casing. Wear ring leakage, on the other hand, causes a radial flow which tends to reduce disk friction.

Disc friction effects are more evident in low specific speed (Ns) pumps. (Refer to Section 218 for discussion of specific speed.) These pumps tend to have large diam-eter, narrow shaped impellers as shown in Figure 200-15. Figure 200-25 shows the typical variation of pump losses with Ns. For low Ns impellers (Ns < 1000), disc friction accounts for 15% or more loss in efficiency.

Disc friction horsepower losses can be estimated as follows:

HP = 1.83(U/100)3 (D/10)2 (S.G.)(N)April 2009 19992009 Chevron USA Inc. All rights reserved. 200-43

200 Centrifugal Pumps Pump Manualwhere:U = Peripheral velocity of impeller, Ft/sec

D = Outside diameter of impeller, inches

S.G. = Specific gravity of fluid at pumping temperature

N = Number of impellers

(Eq. 200-9)

Other calculation methods are available for determining disc friction losses but none are precise because of the effect of other pump design details. For example, disc friction losses increase as impeller-to-casing side clearances increase and as impeller sidewall roughness increases. Losses are also affected by fluid viscosity. For most pumps, this is generally an insignificant effect since fluid viscosity is typi-cally low. (Refer to Section 219 for services where fluid viscosity is greater than water.)

When pump suppliers offer a different number of stages for a specific pump appli-cation, disc friction can clearly account for differences in quoted efficiency. Pump suppliers quoted number of stages will vary most often when the rated capacity is less than 200 gpm or the head is more than 500 feet. Adding a stage or stages and reducing impeller diameters may reduce losses and increase overall efficiency. The addition of stages is not desirable from first cost and maintenance standpoints but the operating cost incentive may more than offset maintenance aspects.

Fig. 200-25 Factors Affecting Overall Pump Efficiency200-44 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsWearing Ring ConsiderationsSimilarly, wearing ring (also commonly called wear ring) clearances can signifi-cantly affect efficiency. Figure 200-26 shows the effect of increasing wear ring clearance on pump horsepower (efficiency). Most petrochemical pumps are designed with impeller specific speeds in the range of 8001500. As shown in Figure 200-25, wear ring losses for a new pump in this Ns range typically average only 34%. For low Ns impellers (Ns < 800), wear ring losses can account for much larger losses (up to 15%) in efficiency. Generally there is little incentive to reduce new wear ring clearances to a minimum. The likely efficiency savings is only 12% with an increased risk of reduced reliability. (See Section 253.)

In service, wear ring clearances gradually increase due to corrosion, erosion, abra-sion, etc. Consequently, efficiency decreases. Clearance increases of 100% or more over as-built (new) clearances typically occur in a 2 to 3 year operating period. This 100% increase results in about a 5% decrease in pump efficiency. Sustaining as-new clearances over long operating periods is much more beneficial from an efficiency standpoint than reducing clearances to minimize losses when the pump is new.

Selection of proper wear ring materials is critical to minimizing efficiency losses and maintaining long-term pump reliability. Section 253 discusses metallic and non-metallic materials available for use in todays pumps.

Fig. 200-26 Effect of Wearing Ring Clearance on Pump HorsepowerApril 2009 19992009 Chevron USA Inc. All rights reserved. 200-45

200 Centrifugal Pumps Pump ManualTrimming Impellers for Efficient OperationSection 216 discusses the affinity law for changes in impeller diameter. This law provides a reasonable estimate as long as impeller diameter changes are within 15% of the original impeller diameter.

When the head developed by a single stage pump with constant speed driver is higher than that actually required, the impeller diameter can be reduced. For multi-stage pumps with constant speed drivers, one or more impellers can be removed. This assumes that the lower head requirement is not a short-term operational condi-tion. The required BHP is reduced directly with a reduction in head.

If the pump is driven by a steam turbine or variable speed motor, the speed can be reduced to obtain the lower head. However, caution should be used since driver effi-ciency may decrease and offset the benefit of the lower pump head.

There are two ways to trim impellers to achieve best efficiency. One way is to trim only the vanes, leaving the shrouds (disc and cover) untrimmed. The second way is to trim both the vanes and the shrouds to the same diameter. In addition to effi-ciency considerations, machining costs, stress levels in unsupported shrouds, stress levels at the vane-to-shroud joint, the effect on the shape of the performance curve, thrust loads and seal cavity operating pressure need to be considered.

Industry practice for both enclosed and semi-open impeller designs is to trim both vanes and shrouds to the same diameter. Exceptions to this practice include high capacity pumps, mixed flow pumps, multistage diffuser pumps and certain pump designs with pumping vane construction on the back shroud (disc).

For multistage diffuser pumps (typically double case types), suppliers often trim only the impeller vanes. Leaving shrouds untrimmed helps guide the flow exiting the impeller as it enters the narrow diffuser passage. There are stress limits which set the amount of unsupported shroud which can be left untrimmed. A typical limit for steel impellers running at 3600 rpm is -inch.

For volute pump designs (typically single stage and multistage, axially split case types), industry practice is to trim both vanes and shrouds to the same diameter. In general, there is no clear cut efficiency advantage to leaving the shrouds untrimmed or to trimming them. Efficiency improvements afforded by added flow guidance provided by the shrouds is approximately offset by the efficiency decrease due to added disc friction. From a manufacturing standpoint, it is easier and less costly to trim vanes and shrouds to the same diameter. Much more care needs to be taken if only the vanes are trimmed. For example, profiling the vane-to-shroud intersection to reduce stress concentrations is important when only the vanes are trimmed. (See Figure 200-14.)

In high capacity, low speed volute design pumps, suppliers sometimes taper the impeller trim from the front to the back shroud. This is done to reduce pressure pulsations due to vanes passing the volutes. Vanes of double suction impellers sometimes are profiled in a V shape for the same reason.

In a few specific cases, it may be advantageous to leave shrouds untrimmed for other reasons. One reason may be the stability of the pumps head-capacity curve. 200-46 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal Pumps(See Figure 200-8.) Also, having the shroud permits vanes to be restored to their original diameter should future head requirements require it.

233 Special Service Pumps

Magnetic Drive or Canned Pumps for Hazardous StocksStuffing boxes have been eliminated in designs called magnetic drive or canned pumps.

Canned pumps have a special electric motor operating under pressure in a liquid-filled chamber adjacent to the pump case. The motor chamber is filled with the liquid pumped. The bearings are usually carbon, lubricated by liquid pumped. These pumps are available in sizes up to 150 HP, 1500 GPM and 600 feet of head; however, they cost considerably more than pumps with stuffing boxes or seals.

Magnetic drive pumps utilize standard horizontal electric motors which are coupled to the pump bearing housing which supports a rotating magnet. The rotating magnet rotates or pulls the impeller rotor supported by product-lubricated, carbon bush-ings inside a sealed case. Like canned motor pumps, these are available in sizes up to 200 HP, 2000 GPM, and 600 feet of head and cost considerably more than conventional centrifugal pumps with seals.

The advantages of completely eliminating stuffing box or seal leakage have led to many installations of these pumps in the Company, primarily in acid and hydrogen sulfide services. However, performance has often been unsatisfactory, primarily because of bearing wear from grit or lack of lubrication. Use these pumps only where the liquid pumped is clean and lubricating, and the pumps are never run dry.

Propeller (Axial-Flow) PumpsThese pumps are used in high volume/low head services. Although available with 2 or 3 stages, most are low-speed, single-stage, vertical pumps. Typical applications are sewage, waste-water lifting, and sump pump out. Lifting 30,000 GPM against 20 ft of head is typical.

Slurry PumpsThese units are in common use and handle abrasive slurries, sand, chemical sludges, plant wastes, and similar products. They are generally low-speed and often are rubber-lined, or cast from very hard materials.

Non-Metallic and Lined PumpsNon-metallic and lined centrifugal pumps are available as a lower cost alternative to pumps constructed of more expensive metallic alloys. Both types are horizontal end-suction pumps designed to ANSI standards (ANSI/ASME B73.1M). They are primarily used in acid, deionized water, and other highly corrosive chemical services.

The wetted components of non-metallic pumps are generally manufactured of glass filament reinforced plastic (FRP). The wetted components of lined pumps are gener-April 2009 19992009 Chevron USA Inc. All rights reserved. 200-47

200 Centrifugal Pumps Pump Manualally manufactured of ductile iron and steel lined with Teflon (PTFE). Both types of pumps are available in capacities to about 800 gpm and head to about 450 feet.

Non-metallic and lined pumps can be considered when the material class goes beyond Alloy 20 (when metals such as nickel, hastalloy, or titanium are required). They should only be considered when there are significant savings over the cost of metallic pumps, or when there is no other practical pumping solution.

234 Application GuidelinesFigures 200-23 and 200-24 show several factors to consider in selection and appli-cation of horizontal and vertical centrifugal pumps. As in selecting the pump cate-gory, there is no straightforward, general procedure to follow in all cases. The design factors are too numerous and often conflict. Consider the design factors most important to your location and refer to the Application Guidelines for information on those factors.

240 Centrifugal Pump DescriptionsThis section illustrates and describes the most commonly used types of centrifugal pumps.

Horizontal Centrifugal Pumps1. Single Stage, API, top/end suction and discharge.

2. Single Stage, ANSI, end suction, top discharge.

3. Single Stage, ANSI, end suction, top discharge, self priming.

4. Single Stage, Double suction, axially split.

5. Multi-stage, API, axially-split case.

6. Multi-stage, API, radially-split case.

Vertical Centrifugal Pumps 1. Single Stage, In-line, ANSI, rigid coupling.

2. Single Stage, In-line, ANSI, integral-shaft.

3. Single-Stage, In-line, ANSI, flexible coupling.

4. Single Stage, In-line, high-speed

5. Single Stage, Sump, bearing supported.

6. Single Stage, Sump, overhung impeller.

7. Multi-Stage, Vertical-Turbine, barrel.200-48 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal Pumps8. Multi-Stage, Vertical-Turbine, deep well.

Pump Description Centrifugal Horizontal single-stage (top/end suction and top discharge) typical API 610 class pump (See Figure 200-27.)

Typical Service Continuous-duty refinery process and critical water service.Typical Head/Capacity Range 50-800 ft/100-10,000 GPMMax Allowable Temperature 350F without cooling

500F with Bearing Cooling800F with Bearing Cooling and Pedestal Cooling

Typical Speed Range Up to 3600 rpmConstruction Features Cast steel and alloy available. Available single or double suction.

Normally closed impellers. Oil lubrication. Packed, single or multi-seals. Radially split. Centerline mounted. Back pullout for maintenance with single suction. Ductile iron or cast iron casings are not available.

Typical Control Method Throttled discharge on flow, level, or pressure control.Advantages More rugged and reliable than ANSI or Industry Standard pumps.

Available in a wide range of pressures and capacities. Lower operating costs since efficiency is usually higher. Available in overhung design up to 900 HP.

Disadvantages and Limitations Most expensive standard centrifugal pump.Specification PMP-MS-983/API 610. Data Sheet API 610, Appendix B. April 2009 19992009 Chevron USA Inc. All rights reserved. 200-49

200 Centrifugal Pumps Pump ManualFig. 200-27 Horizontal, Single-stage, Top/end-suction, Top-discharge, API 610 Class Centrifugal Pump Courtesy of Peerless Pump Co.200-50 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsPump Description Centrifugal Horizontal - single-stage. ANSI B73.1 (end suction, top discharge) (See Figure 200-28.)

Typical Service Chemical. Water. Noncritical hydrocarbon. General purpose.Typical Head-Capacity Range 50-600 ft/50-3500 GPMMax Allowable Temperature 250F recommendedTypical Speed Range Up to 3600 rpmConstruction Features Standard material options for the pump casing and impeller are cast

iron or ductile iron, 316 series stainless, and Alloy 20. Carbon steel is not standard or readily available. Always end suction/top centerline discharge with overhung impeller. Open or closed impellers available. Ball bearing grease or oil lubricated single, tandem, or double seals available. Foot-mounted casing. Back pullout for maintenance.

Typical Control Method Throttled discharge on flow, level, or pressure control.Advantages For each size, ANSI pumps are dimensionally interchangeable from

any manufacturer. Less expensive than API pumps. Wide variety of alloy construction materials available.

Disadvantages and Limitations 150 HP maximum recommended. Carbon steel case is generally not available. Pressures limited to 275 psig @ 60F.

Specification ANSI B73.1. See also PMP-PC-1241 in this manual.Data Sheet PMP-DS-1241-H. April 2009 19992009 Chevron USA Inc. All rights reserved. 200-51

200 Centrifugal Pumps Pump ManualFig. 200-28 Horizontal, Single-stage, End-suction, Top-discharge ANSI Class Centrifugal Pump Copyright 1995 Ingersoll Dresser Pumps. Worthington is a trademark of Ingersoll Dresser Pump Company.200-52 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsPump Description Centrifugal Horizontal single-stage. ANSI B73.1 (end suction, top discharge) self-priming (See Figure 200-29.)

Typical Service For vertical lift when non-pulsating flow desired. Sump pumpout. Tank car unloading.

Typical Head/capacity Range 150-250 ft/0-1000 GPM Max Allowable Temperature 250F RecommendedTypical Speed Range Up to 3600 rpmConstruction Features Same as ANSI Horizontal Typical Control Method Throttled discharge, on/off level control. Advantages Up to 20 ft effective static lift. Eliminates need for foot valve.

Dimensionally interchangeable with all ANSI pumps. More reli-able than submerged vertical sump pumps.

Disadvantages and Limitations Less efficient than standard nonself-priming pumps. May take too long to prime on large suction lines. A mechanical seal may run dry without an external flush.

Company Specification ANSI B73.1. See also PMP-PC-1241 in this manual.Company Data Sheet(s) PMP-DS-1241-H. April 2009 19992009 Chevron USA Inc. All rights reserved. 200-53

200 Centrifugal Pumps Pump ManualFig. 200-29 Horizontal, Single-stage, Self-priming, ANSI Class Centrifugal Pump Courtesy of Goulds Pumps, Inc.200-54 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsPump Description Centrifugal Horizontal single-stage. (double suction, axially split) (See Figure 200-30.)

Typical Service Cooling water circulation. Fire pump. Cargo loading. Crude transfer.Typical Head/Capacity Range 20-1000 ft/1000-50,000 GPM Max Allowable Temperature 250F Recommended Typical Speed Range Up to 3600 rpmConstruction Features Typically cast iron or bronze case (steel case for HCs) and bronze

trim. External sleeve or anti-friction bearings. Horizontal inlet and outlet. Closed impellers. Also available with stainless steel impellers for higher cavitation resistance

Typical Control Method Throttled discharge, system back pressure (cooling water). Advantages Balanced thrust on shaft. Can maintain pump in place. Low NPSH

requirement. Wide range of sizes and capacities.Disadvantages And Limitations More expensive than single suction, overhung pump design. Suction

lines must be carefully designed to avoid nonsymmetrical flow that would channel to one side, resulting in unbalanced thrust and possibly cavitation.

Specification PMP-MS-983/API 610 (hazardous, flammable, and special purpose services). See also PMP-PC-1241 in this manual (general purpose services).

Data Sheet API 610, Appendix B (hazardous and flammable services). April 2009 19992009 Chevron USA Inc. All rights reserved. 200-55

200 Centrifugal Pumps Pump ManualFig. 200-30 Horizontal, Single-stage, Double-suction, Axially (Horizontally)-split Case, Centrifugal Pump Courtesy of Goulds Pumps, Inc.200-56 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsPump Description Centrifugal Horizontal multi-stage. API 610 axially split (See Figure 200-31.)

Typical Service Crude feed. Waterflood. Boiler feedwater. Process. Pipeline.Typical Head/Capacity Range 200-7000 ft/100-5000 GPMMax Allowable Temperature 250F without cooling

400F with Cooling Typical Speed Range Up to 7000 rpmConstruction Features Carbon steel case. CI, steel, stainless steel, or bronze impellers.

Between bearings. Horizontal nozzles, both suction and discharge nozzles located in bottom half casing.

Typical Control Method Throttled discharge on flow, level, or pressure control.Advantages Ease of in-line assembly and inspection. Can be designed with

balanced axial thrust. Eliminates multiple in-line series pumps.Disadvantages and Limitations API 610 limits the axially-split case design to applications below

400F and pumped fluids with specific gravity above 0.70. More complex than single-stage pumps. However, note that pressures to 2000 psig are common in producing water flood applications.

Specification PMP-MS-983/API 610. Data Sheet API 610, Appendix B. April 2009 19992009 Chevron USA Inc. All rights reserved. 200-57

200 Centrifugal Pumps Pump ManualFig. 200-31 Horizontal, Multi-stage, Axially (Horizontally)-split Case Centrifugal Pump Courtesy of Flowserve Corporation200-58 19992009 Chevron USA Inc. All rights reserved. April 2009

Pump Manual 200 Centrifugal PumpsPump Description Centrifugal Horizontal multi-stage. API 610 radially split double case (high pressure, high temperature) (See Figure 200-32.)

Typical Service High pressure process feed pumps. Boiler feedwater. Crude pipeline.Typical Head/Capacity Range 0-10,000 ft/100-5000 GPMMax Allowa