AND PNEUMATICS - DPG PolytechnicIntroduction to Hydraulics and Pneumatics 1.1 Define Ideal fluid? Ans: A fluid, which is incompressible and having no viscosity, is known as an ideal

DPG Polytechnic College Gurugram (HR)

(Mechanical Department)

HYDRAULICS AND PNEUMATICS

January 15

2019 By:Chandra Kumar Diwakar

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LEARNING OUTCOMES

After undergoing this subject, the students will be able to:

• Explain fluid properties, their units and conversion.

• Use and Maintain different types of pressure gauges.

• Calculate velocity and discharge of various liquids.

• Apply Bernoulli’s theorem for calculating pipe diameter and height of pipe from ground.

• Calculate pipe friction and losses in pipelines.

• Specify hydraulic machines for different applications.

• Select maintain and resolve troubles in pumps.

• Apply Pascal’s law in practical applications.

• Maintain hydraulic and pneumatic system. 1.Introduction to Hydraulics and Pneumatics

1.1 Define Ideal fluid?

Ans: A fluid, which is incompressible and having no viscosity, is known as an ideal fluid.

Ideal fluid is only an imaginary fluid as all the fluids, which exist, have some viscosity. 1.2 Define Real fluid ?

Ans: A fluid, which possesses viscosity, is known as real fluid. All the fluids, in actual practice, are real fluids. Example: Water, Air etc.

1.3 DefineNewtonian fluid?

Ans: A real fluid, in which shear stress in directly proportional to the rate of

shear strain or velocity gradient, is known as a Newtonian fluid. Example: Water, Benzine etc.

1.4 Define Non Newtonian fluid?

Ans: A real fluid, in which shear stress in not directly proportional to the rate of shear strain

or velocity gradient, is known as a Non Newtonian fluid. Example: Plaster, Slurries, Pastes

etc.

1.5 Define Ideal plastic fluid ?

Ans: A fluid, in which shear stress is more than the yield value and shear stress is

proportional to the rate of shear strain or velocity gradient, is known as ideal plastic fluid.

1.6 Define Incompressible fluid?

Ans: A fluid, in which the density of fluid does not change which change in external force or

pressure, is known as incompressible fluid. All liquid are considered in this category.

1.7 Define Compressible fluid ?

Ans: A fluid, in which the density of fluid changes while change in external force or pressure, is known as compressible fluid. All gases are considered in

this category.

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Graphical representation of different fluids:

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1.8.Questions on Fluid Properties: 1.8.1DefineDensity ? Ans:Density of a fluid is defined as the mass of the fluid per unit volume.

Mathematically it is defined as the ratio of the mass to the volume of the fluid.

ρ= Mass/Volume

It is depends on the mass and size of the atom of the fluid. Fluids have same volume and different mass have different density.

The SI unit of density is Kg/m3. It is generally denoted by ρ

1.8.2Define Specific gravity?

Ans:It is density of a fluid compared to the density of water which is 1000 Kg/m3. It

shows the substance is how much heavy compare to water.

Mathematically it is defined as the ratio of the density of a fluid to the density of water.

S= (Density of Fluid)/(Density of Water).

If th`e value of specific gravity is greater than one it means the fluid is heavy compared to water and if that fluid mix with water the fluid remain downside of the mixture. If specific gravity is less than one means the fluid is light and can flow over the water in a mixture.

It is a unit less quantity and shown by the S.

1.8.3 DefineViscosity?

Ans:The property of fluid due to which, a fluid layer which is flowing with a velocity U,

exerts a resistance force on the other layer known as viscosity.

It is a property which offers the resistance force in the flow. A fluid has more viscosity has less flow velocity compare to a fluid has less viscosity. For example oil has more viscosity compared to water.

Viscosity of a liquid increases with decreasing in temperature and viscosity of gas increases with increasing in temperature.

According to newton’s law of viscosity, the shear stress is directly proportional to the velocity gradient. The constant of the proportionality is known as viscosity. Mathematically τ = µ du/dy

Where µ is known as dynamic viscosity. The unit of dynamic viscosity is Pa-s or N-s/m2.

There are two types of viscosity used in fluid mechanics one is known as dynamic viscosity (µ) and other on is known as kinematic viscosity (ν). The kinematic viscosity is ratio of the dynamic viscosity to the density of the fluid. ν = µ/ρ

The SI unit of kinematic viscosity is m2/s.

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1.8.4 DefineSpecific Weight ? Ans:It is defined as weight of fluid per unit volume.

Mathematically, it is defined as the ratio of the weight to the volume of the fluid.

w= (Weight of the fluid)/(Volume of the fluid)

It can also be expressed as w= ρ*g

The SI unit of the specific weight is N/m3.

1.8.5 Define Specific volume? Ans:It is the reciprocal of the density or we can say that it is the volume of the fluid per unit mass.

Specific Volume= (Volume of the fluid)/(Mass of the fluid)

The SI unit of specific volume is m3/Kg.

1.8.6 Define Vapor Pressure? Ans:The pressure exerted by its vapor in phase equilibrium with its liquid at a given temperature is known as vapor pressure.

The vapor pressure of the fluid is increased by increasing in temperature.

It the liquid pressure drops below its vapor pressure at a given temperature, the liquid starts to evaporate. Petrol have more vapor pressure with respect atmospheric pressure at atmospheric temperature, so it starts to evaporate while water doesn’t

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2. Pressure and its Measurement :

2.1 Define pressure ?

Ans:Pressure (P) expresses the magnitude of normal force (F-N) per unit area (A-m2) applied on a surface

Units: Pa(= N/m2), psi(=lbf/in2), bar (=105 Pa=100 kPa), mbar (=100 Pa=1

hPa), atm (=101.3 kPa), mmHg (or Torr), inHg, etc. Note: For every Unit:

hUnit=hectoUnit=100 Unit. Where Pabs : Absolute pressure Patm : Atmospheric pressure (standard is: 101.3 kPa =14.696 psi=760 mmHg=29.92 inHg)

2.1.1 Define Absolute Pressure?

Ans:The actual pressure at a given position is called the absolute pressure and it is measured

relative to absolute vacuum. One concept remembers in mind that to measure any quantity we

required a base line with respect we are going to measure it.

2.1.2 Define Gauge Pressure?

Ans:When we take atmospheric pressure as reference to measure pressure of any system, the

measured pressure is known as gauge pressure. Most of pressure devices work in atmospheric

condition always measure gauge pressure. We can convert this gauge pressure in absolute

pressure by adding atmospheric pressure in gauge pressure. P (absolute) = P(Gauge) + P (Atmospheric)

2.1.3 Define Vacuum pressure?

Ans:Pressure below atmospheric pressure is called vacuum pressure and is measured by vacuum

gauges that indicate the difference between the atmospheric pressure and absolute pressure. P (vacuum) = P (Atmospheric) – P (Absolute)

This is all about gauge pressure and absolute pressure. If you have any query regarding this

article, ask by commenting. If you like this article, don’t forget to share it on social networks.

Subscribe our website for more informative articles. Thanks for reading it.

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2.2 Explain Bourdon Tube.

Ans:The device was invented by Eugene Bourdon in the year 1849. The basic idea behind the

device is that, cross-sectional tubing when deformed in any way will tend to regain its circular

form under the action of pressure. The bourdon pressure gauges used today have a slight

elliptical cross-section and the tube is generally bent into a C-shape or arc length of about 27

degrees. The detailed diagram of the bourdon tube is shown below.

Bourdon Tube Pressure Gauge As seen in the figure, the pressure input is given to a socket which is soldered to the tube at the

base. The other end or free end of the device is sealed by a tip. This tip is connected to a

segmental lever through an adjustable length link. The lever length may also be adjustable. The

segmental lever is suitably pivoted and the spindle holds the pointer as shown in the figure. A

hair spring is sometimes used to fasten the spindle of the frame of the instrument to provide

necessary tension for proper meshing of the gear teeth and thereby freeing the system from the

backlash. Any error due to friction in the spindle bearings is known as lost motion. The

mechanical construction has to be highly accurate in the case of a Bourdon Tube Gauge. If we

consider a cross-section of the tube, its outer edge will have a larger surface than the inner

portion. The tube walls will have a thickness between 0.01 and 0.05 inches.

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Working As the fluid pressure enters the bourdon tube, it tries to be reformed and because of a free tip

available, this action causes the tip to travel in free space and the tube unwinds. The

simultaneous actions of bending and tension due to the internal pressure make a non-linear

movement of the free tip. This travel is suitable guided and amplified for the measurement of the

internal pressure. But the main requirement of the device is that whenever the same pressure is

applied, the movement of the tip should be the same and on withdrawal of the pressure the tip

should return to the initial point. A lot of compound stresses originate in the tube as soon as the pressure is applied. This makes

the travel of the tip to be non-linear in nature. If the tip travel is considerably small, the stresses

can be considered to produce a linear motion that is parallel to the axis of the link. The small

linear tip movement is matched with a rotational pointer movement. This is known as

multiplication, which can be adjusted by adjusting the length of the lever. For the same amount

of tip travel, a shorter lever gives larger rotation. The approximately linear motion of the tip

when converted to a circular motion with the link-lever and pinion attachment, a one-to-one

correspondence between them may not occur and distortion results. This is known as angularity

which can be minimized by adjusting the length of the link.

2.3 Explain Diaphragm Pressure.

Ans:A diaphragm pressure transducer is used for low pressure measurement. They are

commercially available in two types – metallic and non-metallic. Metallic diaphragms are known to have good spring characteristics and non-metallic types have

no elastic characteristics. Thus, non-metallic types are used rarely, and are usually opposed by a

calibrated coil spring or any other elastic type gauge. The non-metallic types are also called slack

diaphragm.

2.3.1 Explain diaphrabm gauge

Ans :Working The diagram of a diaphragm pressure gauge is shown below. When a force acts against a thin

stretched diaphragm, it causes a deflection of the diaphragm with its centre deflecting the most.

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Diaphragm Gauge

Since the elastic limit has to be maintained, the deflection of the diaphragm must be kept in a

restricted manner. This can be done by cascading many diaphragm capsules as shown in the

figure below. A main capsule is designed by joining two diaphragms at the periphery. A pressure

inlet line is provided at the central position. When the pressure enters the capsule, the deflection

will be the sum of deflections of all the individual capsules. As shown in figure (3), corrugated

diaphragms are also used instead of the conventional ones.

Diaphragm Pressure Transducer

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Corrugated designs help in providing a linear deflection and also increase the member strength.

The total amount of deflection for a given pressure differential is known by the following

factors:

1. Number and depth of corrugation 2. Number of capsules 3. Capsule diameter 4. Shell thickness 5. Material characteristics

Materials used for the metal diaphragms are the same as those used for Bourdon Tube. Non-

metallic or slack diaphragms are used for measuring very small pressures. The commonly used

materials for making the diaphragm are polythene, neoprene, animal membrane, silk, and

synthetic materials. Due to their non-elastic characteristics, the device will have to be opposed

with external springs for calibration and precise operation. The common range for pressure

measurement varies between 50 Pa to 0.1 MPa.

The best example for a slack diaphragm is the draft gauge. They are used in boilers for indication

of the boiler draft. The device can control both combustion and flue. With the draft, usually of

pressure less than the atmosphere, connected, the power diaphragm moves to the left and its

motion is transmitted through the sealing diaphragm, sealed link and pointer drive to the pointer.

The power diaphragm is balanced with the help of a calibrated leaf spring. The effective length

of the spring and hence the range is determined by the range adjusting screw. By adjusting the

zero adjustment screw, the right hand end of the power diaphragm support link as also the free

end of the leaf spring, is adjusted for zero adjustment through the cradle.

3.Flow of fluid:

3.1 Explain Steady and Unsteady flow.

Ans: The flow in which characteristics of fluid like velocity, temperature, pressure, density etc.

do not changes at a point with time is known as steady flow. The flow in which characteristics of

fluid changes with time at a same point is known as unsteady flow.

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3.2 Explain Uniform and Non Uniform flow.

Ans: The fluid flow in which the properties of fluid like pressure, temperature, velocity

etc. changes with respect time but does not changes with respect position is known as

uniform flow. The fluid flow, in which the properties of fluid like pressure, temperature,

velocity etc. changes with respect time as well as with respect position, is known as non-

uniform flow.

3.3 Explaion Laminar and turbulence flow.

Ans: The fluid flow, in which the adjacent layers do not cross each other and move along

we define path is known as laminar flow. In this flow, fluid flows along the straight line.

The flow in which adjacent layers cross each other and do not move along well defined

path is known as turbulence flow.

3.4 Explain Rotational and Ir-rotational flow.

Ans: If the fluid particles flowing along stream lines also rotate about their own axes,

then flow is known as rotational flow. If fluid particles do not rotate about their own axes,

then flow is known as irrotational flow.

3.5 Explain Compressible and In-compressible flow .

Ans:If the density of fluid varies from point to point in the flow, the flow is known as

compressible flow. If the density of fluid remains constant through the flow, the flow is

known as incompressible flow. We have discussed about types of fluid flow. If you have

any doubt regarding this article, ask by commenting. If you like this article, don’t forget

to share it on social networks. Subscribe our website for more informative articles.

Thanks for reading it.

3.6 Steady and Unsteady flow?

Ans: The flow in which characteristics of fluid like velocity, temperature, pressure,

density etc. do not changes at a point with time is known as steady flow. The flow in

which characteristics of fluid changes with time at a same point is known as unsteady

flow.

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3.7 Uniform and Non Uniform flow?

Ans: The fluid flow in which the properties of fluid like pressure, temperature, velocity

etc. changes with respect time but does not changes with respect position is known as

uniform flow. The fluid flow, in which the properties of fluid like pressure, temperature,

velocity etc. changes with respect time as well as with respect position, is known as non-

uniform flow. .

3.8 Compressible and In-compressible flow?

Ans: If the density of fluid varies from point to point in the flow, the flow is known as

compressible flow. If the density of fluid remains constant through the flow, the flow is

known as incompressible flow. We have discussed about types of fluid flow. If you have

any doubt regarding this article, ask by commenting. If you like this article, don’t forget to

share it on social networks. Subscribe our website for more informative articles. Thanks

for reading it.

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4. Hydraulic Machines 4.1 Hydraulic Press : Principle, Construction, Working with Applications Defination: Hydraulic press is a mechanical device which is based on the ‘Pascal’s law’ which states that equal intensity of pressure exerts on all the directions in a closed system. It applicable here in such a way that if there is any pressure change at one point in a closed system then same intensity of pressure will change at other point in the same system. Construction and working of Hydrualic Press: In practical hydraulic press system, generally multiple rams are assembled together. The number of rams used depends upon the working load. In hydraulic press multiple rams of small sizes are preferred instead of a single large size ram to control the thrust forces because it is easy to control the thrust forces on small size as compare to large size. In press assembly one side/table is always fixed while the other is moving by the application of ram force and in between fixed as free side pressing operation is take place. Ram is operated by the hydraulic pressure of fluid. The high pressure liquid is supplied by using pump and hydraulic accumulator. Hydraulic accumulator works as the junction between the pump and the rams. Hydraulic accumulator stores the high pressure liquid when press is at stationary position. Hydraulic press is used where high thrust is required for operation.

Applications:

▪ The major application of the hydraulic press is in industry where big size metal objects

transform into thin sheets by the application of pressure force.

▪ Sheet metal operations such as drawing, deep drawing, punching and blanking etc

▪ In crushing of scraps and old vehicles.

▪ In Packaging industry.

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4.2 Hydraulic Jack : Principle, Construction, Working with Applications Defination: A jack is a mechanical device which uses a screw thread or a hydraulic cylinder to lift heavy loads or apply great linear forces. The most common forms of jacks available in the market are Scissor car jacks, House jacks, Hydraulic jacks, Pneumatic jacks and Strand jacks that are extensively used in Construction, Industrial, Automobile and Engineering segments. Construction and working of Hydrualic jack: It consist of two cylinders of different sizes which are connected together by a pipe and a hydraulic fluid or oil. The hydraulic fluid is incompressible and using a pump plunger is forced into the cylinder of the jack. Oil is used because of its stable and self lubricating nature. When the plunger pulls back, oil is drawn out of the reservoir and it goes inside the pump chamber. When the plunger moves forward, the oil is pushed back into the cylinder. This oil movement builds up pressure in the cylinder. And it is this pressure which leads to the working of the hydraulic jack. It also find usage in workshops and also lift elevators in low and medium rise buildings. These can be segmented into two types: Bottle Hydraulic Jack and Floor Hydraulic Jack. Bottle are portable in design; in these the piston is in a vertical position and it supports a bearing pad which touches the object being lifted. Bottle Hydraulic are most appropriate for lifting vehicles (cars, trucks, SUVs, trailers), houses and other heavy objects. In a Floor Jacks, the piston is in a horizontal piston and there is a long arm which provide the vertical motion to a lifting pad. There are wheels and castors in floor jacks.

The working principle of all hydraulic jacks is common but these differ in their shapes and sizes. Hydraulic jacks with varied sizes and specifications are used to lift different types of heavy equipment and vehicles such as bulldozers, forklifts, elevators, trolleys & trailers and

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excavators. These can also be found in household equipments as well like door stoppers, cars, bikes etc. Hydraulic Jacks are high in demand across the globe owing to their sturdy construction, reliable & hassle free operation, unparalleled performance, user-friendly design and less maintenance. 4.3 Hydraulic Accumulator : Principle, Construction, Working with Applications Defination: Hydraulic accumulator is a mechanical device used in hydraulic applications. It works as an intermediate device between supply lines of hydraulic fluid from pump to required machines like hydraulic lift, hydraulic press, hydraulic cranes etc. Constructions and working: A simple hydraulic accumulator consists of a cylinder with inlet and outlet ports for the hydraulic fluid, inlet are attached with the pump where as outlet is connected with the operational machine. Cylinder consists of a ram with reciprocating motion inside the cylinder and having some weight on the top of the ram. The arrangement of the ram and cylinder should be vertical in position.

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Pump continuously supplies the hydraulic fluid to the operating machine through the accumulator, when there is no requirement of the fluid the outlet becomes close. This time continuous supply from the pump raises the ram/plunger in the upward position gradually till the extreme end or until the outlet is open. This operation helps to store the hydraulic energy inside the accumulator for a small period of time. As the operating machine require pressurized fluid for the power stroke then the outlet port becomes open and ram with weights on the top starts slides downward gradually which results high pressurized liquid is delivered to the operating machine during its power stroke. This whole operation repeated continuously and helps us to do difficult tasks with small investment of energy in daily life. 4.4 Hydraulic Brake: Principle, Construction, Working with Applications Defination: Hydraulic brake is a type of braking system which is widely used in the automobiles with the application of the hydraulic fluid. The working principle of hydraulic braking system is purely based upon Pascal’s law, which states that the intensity of pressure exerted inside a closed system by the liquid is always equal in all the directions. Constructions and working:

1. Master cylinder: It is the main part is the whole assembly. It works as a hydraulic actuator which has a piston-cylinder arrangement. It is responsible for the conversion of mechanical force into the hydraulic force. As the brake pedal is pressed the fluid in the master cylinder compressed and exerts pressure which is transmitted to Brake assembly through the hydraulic lines.

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2. Brake pedal and mechanical linkage: Brake pedal works as the input to the master cylinder or we can say that whole assembly will start working when the brake pedal is pressed. It is pressed manually when we have to stop or slow down the running body. It is further attached with little mechanical linkage such as spring which helps in retraction of the pedal further it connects to master cylinder. After the execution of the brake pedal, the master cylinder comes into the working. 3. Hydraulic/brake fluid reservoir: It is kind of a small tank for the braking fluid. It is directly attached to the master cylinder. For the proper operation of hydraulic braking. It is necessary to maintain the accurate amount of braking fluid in the whole assembly. Sometimes due to small leakages the level of fluid goes down into the master cylinder so to maintain the proper amount of brake fluid in the working operation a reservoir is required. The braking fluid goes into the master cylinder from the reservoir when it is required. 4. Hydraulic lines: Hydraulic lines are the connections between the various components of the braking system. Braking fluid travels through these lines from master cylinder to brake. These are the small diameter pipes which replace the different types of mechanical linkage in case of mechanical brakes. 5. Brake caliper (In case of disc brake): Brake calipers are the parts of the braking system in case of disc brakes which execute the brake. Inside the brake calipers pistons are mounted which is responsible for the braking. The brake pads are also attached with the piston. Calipers are mounted on the periphery of the disc. The disc brake is externally applied braking system. A disc is mounted in between the calipers. 6. Drum cylinder (In drum brake system): Drum cylinder is a kind of small cylinder which is used in the Drum brakes and situated inside the brake drum and connected to both the brake shoes. A drum brake is internally applied brakes. Working: The working of the hydraulic braking system is very simple. To execute the brake we have two types of components one is disc brake and the other is a drum brake. The initial working for both the types is same but the execution technique is different. The disc brake is externally applied brake by means of the brake caliper and disc whereas drum brakes are internally applied by means of brakes shoes and brake drum. The working of both the types is as follow: Disc brake: Working of the hydraulic braking system having disc brake starts with the pressing of brake pedal. Due to compressive action the fluid the brake fluid compressed into the master cylinder by means of piston-cylinder arrangement. The compressed fluid creates pressure in the hydraulic supply lines and then transfers whole pressure energy at the brake caliper of the disc brake. A disc is mounted in between the calipers. Both the calipers have piston arrangement and brake pads are mounted on the piston. As the brake pedal is pressed then the movement in the pistons starts i.e. both the pistons start moving towards the discs and at the end brake caliper compresses the disc and brake executed then running parts stop.

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Drum brake: The initial working of the drum brake is the same as disc brake the difference is in the execution of the brake. In case of drum brake; drum and drum cylinder is used at the place of disc and caliper. As the brake pedal is pressed the high-pressure fluid goes in the drum cylinder of drum brake by means of hydraulic lines. As the fluid reaches into the drum cylinder it starts expands and presses the brake shoes and brake is applied. When we release the brake pedal then spring between both the brake shoes is responsible for the releasing of the brake. After the releasing the brake pedal fluid from the brake cylinder return back and brake released. 5.Pumps and Water Turbines:

5.1 Centrifugal Pump:

Principle: This pump works on basic principle of change in angular momentum. It state that the change in the angular momentum of a rotating particle is equal to the applied force. It means when a certain amount of liquid is rotated with the help of external agency means turbines or electric motor or external force, a centrifugal force acts on it which further turns into pressure. In addition to, this as liquid passes through revolving wheel then there is change in angular momentum of rotating wheel or impeller which generates more amount of pressure. In short, in a centrifugal pump kinetic energy of impeller is converted into pressure energy of fluid which is used to raise up it to certain height. Due to centrifugal force acting on water or fluid, it is lifted up to particular height. So these pump is called as centrifugal pump

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1. Rotating components:It consists of a shaft and an impeller A.) Impeller: It is the main part of centrifugal pump. It provides centrifugal acceleration to the liquid. Impeller has again its sub-types.

a.) Open impeller: This impeller is without crown and base plate. This type of impeller is useful in removing liquid containing solid particles such as water containing sand, paper pulp etc. b.) Closed impeller: Closed impeller has vanes which contain cover plates on both sides. It is mostly used in obtaining pure water.

c.) Semi-open impeller:It has only base plate and don’t has any crown plate. It is comfortable with fluid containing charged debris. B.) Shaft: It is used to rotate the impeller. It is designed to transmit torque encountered while starting and operating time of impellers and other rotating components. C.) Shaft sleeve: Sleeves prevent centrifugal pump shaft from corrosion and leakage points. It should be taken care that sleeves should be sealed at one end. 2.Stationary components:It consist of casing, bearings, suction pipe. A.) Casings: These casings are similar to the casings of a turbine. There are two types of casing: a.) Volute casings: Volute is the funnel of increasing area and generally curve in shape. As cross sectional area of funnel decreases velocity of liquid decreases with increasing pressure. These are created to have a higher head. To balance the pressure on shaft of centrifugal pump is the focus behind developing volute casings. b.) Circular or Vortex casings: These have vanes which surrounds impeller periphery and convert kinetic energy into pressure energy. B.) Suction pipe: The lower end of a suction pipe is dipped in water which is to be lifted up and the other end is connected to the inlet of centrifugal pump. Strainer and foot valve present at the lower end of the suction pipe help to remove waste material from water such as leaves, sand and to allow the flow of water only in upward direction, respectively.

5.1.1 Types Centrifugal pump: Following is the classification of centrifugal pump.

A.) According to the type of casing:

a) Turbine pump: It consists of vanes which surround impeller on a diffuser ring.

These vanes and diffuser ring both are in stable position and distance between vanes

provide a direction to the flow of liquid. Fluid leaving impeller flows through these

empty spaces with high pressure. After leaving vanes the fluid goes into casings

which may be circular, concentric or volute shape. It has been founded that we can

convert 75% of kinetic energy into pressure energy. Disadvantage of these pumps is

that they are very expensive. b) Volute pump: In this pump, impeller is covered by volute chamber. These volute

casing may be created in such a way that having equal velocities of liquid leaving impeller and entering the pump. If it is designed as mentioned above then there is

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very less loss of energy but kinetic energy cannot be converted into more useful potential energy.

B.) According to the impeller number per shaft:

Centrifugal pumps may be classified as multi-stage and single-stage depending upon

the number of impellers. Multi-stage pump has two or more series joined impellers

enclosed in same casing. Single-stage pump has only one impeller mounted on the shaft. C.) According to the direction of liquid flow through impeller:

These pumps may be classified on the basis of direction of flow of liquid through the impeller as axial flow pump, mixed flow pump and radial flow pump.

5.1.2 Working of centrifugal pump: Before discuss about its working you should learn about what is priming and why it is essential for proper working of centrifugal pump. Priming: Priming is the most basic and first step in the working of centrifugal pump. The process of filling the casing, suction pipe and delivery pipe upto the delivery valve before starting the pump is known as priming. In order to remove the air gap present in pump, it is filled by liquid. Pressure developed inside the pump is directly proportional to the density of liquid in it. If there is air in pump and an impeller is allowed to rotate then pressure energy cannot be developed as density of fluid is less due to presence of air. So it is very important to prime a centrifugal pump carefully.

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Its working can be summarized into following points:

First priming is done before starting the pump. Delivery valve is still kept closed.

Now the motor starts. The rotation of impeller in the casing full of liquid accelerates liquid and there is generation of powerful centrifugal force which results in enhancement in liquid pressure.

This increase in pressure is directly proportional to the square of angular velocity and distance of point from the axis.

Therefore, if the impeller rotates with faster speed, there is greater amount of production of required pressure energy.

Now the delivery valve open and allow liquid to flow at desired location.

Liquid comes out of impeller with high velocity. This increasing kinetic energy due to

increased velocity can be wasted in eddies which result in decreasing the efficiency of

pump. So safety should be taken to reduce this speed as that of lower velocity of delivery

pipe.

Advantages: Centrifugal pumps don’t have any leakage issue.

They are able to pump hazardous as well as sensitive fluids.

There is also no problem of heat transfer as the space between the motor and chamber is sufficiently large.

There is no loss of power due to friction and they are very simple in structure and easy in handling.

Disadvantages:

Magnetic resonance in centrifugal pump results in small loss of energy.

The risk of the clogging of pipe may arise due to particle attractive nature of magnetic drive.

Vibrations due to surrounding atmosphere can damage these pumps.

The risk of cavitations is always there.

Applications:

These pumps are used in buildings for pumping the regular water.

They are used in the fire protection related services.

Centrifugal pumps are used to transfer lactose and other drugs in pharmaceutical industry.

They are also used in coolant recirculation, refrigerants.

These pumps are used in sprinkling, irrigation, drainage.

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5.2 Hydraulic Turbine: 5.2.1 Working Principle: According to Newton’s law a force is directly proportional to the change in momentum. So if there is any change in momentum of fluid a force is generated. In the hydraulic turbine blades or bucket (in case of Pelton wheel) are provided against the flow of water which change the momentum of it. As the momentum is change a resulting pressure force generated which rotate the rotor or turbine. The most important phenomenon is the amount of change in momentum of water which is directly proportional to force. As the change in momentum high the force generated is high which increase the energy conversion. So the blade or buckets are designed so it can change maximum momentum of water. This is the basic principle of turbine. These turbines are used as hydro electric power plant.

5.2.2 Types hydraulic turbine: The hydraulic turbine can be classified according to the energy available at inlet, direction of flow of water, Specific speed, head available at inlet etc. These all types are described as below.

1. According to Type of Energy Available at Inlet:

a) Impulse Turbine:

Impulse turbine is those turbines which are use impulse energy or we can say kinetic

energy of water to rotate the turbine. In this type of hydraulic turbine all pressure

head or pressure energy is converted into velocity head or kinetic energy at the inlet

of turbine by using nozzle. This high speed water jet strikes the blade or bucket of

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turbine which develop a force which rotate it. Only kinetic energy changes at the inlet

and outlet of turbine and the pressure of water remain same. This kind of turbine is

known as impulse turbine. There are various design available of impulse turbine but

the Pelton wheel most suited for it. These are generally high head and low discharge

hydraulic turbine.

b) Reaction Turbine:

As the name implies these turbines is used pressure energy of water to rotate the

turbine. In practically no turbine can purely used pressure energy. So it used both its

pressure energy and kinetic energy. These turbines rotate partially due to impulse

action and partially due to pressure change over the runner blades. The water flow

over blades covert both its kinetic energy as well as pressure energy into force and

rotate the turbine. The change in pressure energy of water known as degree of

reaction of the turbine. So it is known as reaction turbine. They are generally low

head, high discharge turbine.

2. According to Direction of Flow:

a) Tangential Flow Turbine:

In this hydraulic turbine the water flow through tangent of runner. The water jet

strikes the runner tangentially and rotates the turbine. Example Pelton wheel turbine

Pelton Turbine

b) Radial Flow Turbine: In this type of turbine the water flows in radial direction. This is subdivided into two types. The first one is known as inward radial flow in which the water flows from periphery to the center. Example Francis turbine. Second one is known as outward flow radial turbine in which water flow towards periphery from center.

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Francis Turbine

c ) Axial Flow Turbine:

In this hydraulic turbine, the water flow from the axis of turbine. Example :Kaplan turbine

Kaplan Turbine

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c) Mixed Flow Turbine:

When the water enters the turbine radically and exit axially or vice versa, it is known as mixed flow turbine.

3.) According to Head of Water Available at Inlet:

Medium Head Turbine: If the water level varies from 30 -130 m from the axis of the turbine, it is known as medium head turbine. Example Francis Turbine

Low Head Turbine: If the water level is below 30 meter from the axis of turbine, it is known as low head turbine. These hydraulic turbine required high discharge rate to work efficiently. Example Kaplan turbine.

4.) According to Specific Speed of Turbine:

Low Specific Speed Turbine: If the specific speed is less than 50 the turbine is

considered as low specific speed turbine. Example Pelton wheel.

Medium Specific Speed Turbine: If the specific speed is between 50 – 150, it is considered as medium specific speed turbine. Example Francis Turbine

High Specific Speed Turbine: If the specific speed of turbine is above 250 it is known as high specific speed turbine. Example Kaplan Turbine

5.2.2.1 Advantages and Disadvantages:

Hydro power plant or we can say that hydraulic turbines are widely used form the last decades. It is an efficient renewable energy source. There are many up and downs in every project so there are also have many advantages and disadvantages which are describe below.

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Advantages:

It is a renewable energy source. Water energy can be used again and again.

The running cost of turbine is less compare to other.

It has high efficiency.

It can be control fully. The gate of dam is closed when we does not need electricity and can be open when we needed.

Dams are used from very long time so it can be used for power generation.

It does not pollute environment.

It is easy to maintain.

The dam constructed for hydraulic turbine can become a tourist place.

Disadvantages:

Initial cost is very high. It takes several decades to become profitable.

It can destroy the natural environment at site. Large dam cause big geological damages.

It can develop at only few sites where proper amount of water is available.

This is all about Hydraulic turbine working, types and advantages and disadvantages. If you have any query regarding this article, ask by commenting. If you like this article, don’t forget to share it on social networks. Thanks for reading it.

Long Questions :

Q.5.1 Write The Difference between Centrifugal Pump and Reciprocating Pump.

Ans:

S. No. Centrifugal pump Reciprocating pump

It is one of the rotary pumps which used kinetic It is a positive displacement type pump which is

1. energy of impeller. forced by piston.

2. It continuously discharges the fluid. It does not discharge the fluid continuously.

In centrifugal pump the flow rate decreases which The pressure does not affect flow rate in

3. increasing the pressure. reciprocating pumps.

4. It is used for pumping high viscous fluid. It is used for pump low viscous fluid.

In this pumps discharge is inversely promotional to In reciprocating pump viscosity of fluid does

5. the viscosity of fluid. not affect the discharge rate.

Efficiency of these pumps are low compare to

6. reciprocating pump. Efficiency is high.

7. Centrifugal pump have problem of priming. It does not have any problem of priming.

It uses piston cylinder device to transfer energy

8. It uses impellers to transfer energy to fluid. to fluid.

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Q.5.2 Write the difference between Impulse and Reaction Turbine.

Ans:

These are heavier compare to centrifugal

9. They are lighter than reciprocating pumps. pump.

10. It gives higher discharge at low heads. These gives higher heads at low discharge.

11. It is less costly. These are costly.

12. These pumps required less maintenance. These required higher maintenance.

Centrifugal pumps are easy to install. These These pumps are difficult to install. These

13. required less floor space. required more floor area.

It is mostly used for domestic purpose and where These are mostly used in industries and high

14. higher discharge at low head required. viscous fluid pumped at a high head.

Impulse Turbine Reaction Turbine

1. In impulse turbine only kinetic energy is used to 1. In reaction turbine both kinetic and pressure energy is

rotate the turbine. used to rotate the turbine.

2. In this turbine water flow through the nozzle and 2. In this turbine water is guided by the guide blades to

strike the blades of turbine. flow over the turbine.

3. All pressure energy of water converted into kinetic 3. In reaction turbine, there is no change in pressure

energy before striking the vanes. energy of water before striking.

4. The pressure of the water remains unchanged and is 4. The pressure of water is reducing after passing

equal to atmospheric pressure during process. through vanes.

5. Water may admitted over a part of circumference or 5. Water may admitted over a part of circumference or

over the whole circumference of the wheel of turbine. over the whole circumference of the wheel of turbine.

6. In impulse turbine casing has no hydraulic

function to perform because the jet is at atmospheric 6. Casing is absolutely necessary because the pressure at

pressure. This casing serves only to prevent splashing of inlet of the turbine is much higher than the pressure at

water. outlet. It is sealed from atmospheric pressure.

7. This turbine is most suitable for large head and lower 7. This turbine is best suited for higher flow rate and

flow rate. Pelton wheel is the example of this turbine. lower head situation.

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Multiple Choice Questions on the bases of above topic :

1. Power required to drive a centrifugal pump is directly proportional to __________ of its

impeller.

A. diameter

B. square of diameter

C. cube of diameter

D. fourth power of diameter

2. The mechanical efficiency of an impulse turbine is

A.

ratio of the actual power produced by the turbine to the energy actually supplied by the

turbine

B. ratio of the actual work available at the turbine to the energy imparted to the wheel

C. ratio of the Work done on the wheel to the energy of the jet

D. none of the above

3. In a Kaplan turbine runner, the number of blades are generally between

A. 2 to 4

B. 4 to 8

C. 8 to l6

D. 16 to 24

4. Discharge of a centrifugal pump is

A. directly proportional to diameter of its impeller

B. inversely proportional to diameter of its impeller

C. directly proportional to (diameter)2 of its impeller

D. inversely proportional to (diameter)2 of its impeller

5. The static head of a centrifugal pump is equal to the __________ of suction head and delivery

head.

A. product

B. difference

C. Sum

D. all of these

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6. The speed of a turbine runner is

A. directly proportional to H1/2

B. inversely proportional to H1/2

C. directly proportional to H3/2

D. inversely proportional to H3/2

7. Discharge of a centrifugal pump is (where N = Speed of the pump impeller)

A. directly proportional to N

B. inversely proportional to N

C. directly proportional to N2

D. inversely proportional to N2

8. In a reaction turbine, the draft tube is used

A. to run the turbine full

B. to prevent air to enter the turbine

C.

to increase the head of water by an amount equal to the height of the runner outlet above

the tail race

D. to transport water to downstream

9. Multi-stage centrifugal pumps are used to

A. give high discharge

B. produce high heads

C. pump viscous fluids

D. all of these

10. Which of the following pump is preferred for flood control and irrigation applications?

A. Centrifugal pump

B. Axial flow pump

C. Mixed flow pump

D. Reciprocating pump

ANSWERS :

1.D 2.B 3.B 4.D 5.C 6.A 7.A 8.C 9.B 10.C

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6. Oil power Hydraulic and Pneumatic systems

6.1 Introduction:

In the industry we use three methods for transmitting power from one point to another.

Mechanical transmission is through shafts, gears, chains, belts, etc. Electrical transmission is

through wires, transformers, etc. Fluid power is through liquids or gas in a confined space. In this

chapter, we shall discuss a structure of hydraulic systems and pneumatic systems. We will also

discuss the advantages and disadvantages and compare hydraulic, pneumatic, electrical and

mechanical systems.

6.2Applications of fluid power:

Agriculture Tractors; farm equipment such as mowers, ploughs,

chemical and water sprayers, fertilizer spreaders,

harvesters

Automation Automated transfer lines, robotics

Automobiles Power steering, power brakes, suspension systems,

hydrostatic transmission

Aviation

Fluid power equipment such as landing wheels in

aircraft.

Helicopters, aircraft trolleys, aircraft test beds,

luggage

loading and unloading systems, ailerons, aircraft

servicing,

flight simulators

Construction For metering and mixing of concrete rudders,

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excavators,

industry/equipment

lifts, bucket loaders, crawlers, post-hole diggers,

road

graders, road cleaners, road maintenance vehicles,

tippers

Defense Missile-launching systems, navigation controls

Entertainment

Amusement park entertainment rides such as roller

coasters

Fabrication industry Hand tools such as pneumatic drills, grinders, borers,

riveting machines, nut runners

Food and beverage

All types of food processing equipment, wrapping,

bottling,

Foundry Full and semi-automatic molding machines, tilting of

furnaces, die-casting machines

Glass industry Vacuum suction cups for handling

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Hazardous gaseous areas Hydraulic fracturing technologies: It involves pumping

large volumes of water and sand into a well at high pressure

to fracture shale and other tight formations, allowing

hazardous oil and gas to flow into the well. However,

hydraulic fracturing has serious environmental and water

pollution related issues.

Instrumentation Used to create/operate complex instruments in space

rockets, gas turbines, nuclear power plants, industrial labs

Jigs and fixtures Work holding devices, clamps, stoppers, indexers

Machine tools Automated machine tools, numerically controlled(NC)

machine tools

Materials handling Jacks, hoists, cranes, forklifts, conveyor systems

Medical Medical equipment such as breathing assistors, heart assist

devices, cardiac compression machines, dental drives and

human patient simulator

Movies Special-effect equipment use fluid power; movies such as

Jurassic park, Jaws, Anaconda, Titanic

Mining Rock drills, excavating equipment, ore conveyors, loaders

Newspapers and periodicals Edge trimming, stapling, pressing, bundle wrapping

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Oil industry Off-shore oil rigs

Paper and packaging Process control systems, special-purpose machines for

rolling and packing

Pharmaceuticals Process control systems such as bottle filling, tablet

placement, packaging

Plastic industry Automatic injection molding machines, raw material

feeding, jaw closing, movement of slides of blow molder

6.3 Basic components of hydraulic system:

Hydraulic systems are power-transmitting assemblies employing pressurized liquid as a

fluid for transmitting energy from an energy-generating source to an energy-using point

to accomplish useful work. Figure shows a simple circuit of a hydraulic system with

basic components.

Load Motor 1 – Off 2 – Forward 3– Return

Pressure Filter regulator

Pump

1 3 2

Direction control valve

Oil tank

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Actuator

Functions of the components shown in Fig. are as follows:

The hydraulic actuator is a device used to convert the fluid power into

mechanical power to do useful work. The actuator may be of the linear type (e.g.,

hydraulic cylinder) or rotary type(e.g., hydraulic motor) to provide linear or rotary

motion, respectively.

The hydraulic pump is used to force the fluid from the reservoir to rest of

the hydraulic circuit by converting mechanical energy into hydraulic energy.

Valves are used to control the direction, pressure and flow rate of a fluid

flowing through the circuit.

The piping shown in Fig. is of closed-loop type with fluid transferred from the storage

tank to one side of the piston and returned back from the other side of the piston to the

tank. Fluid is drawn from the tank by a pump that produces fluid flow at the required

level of pressure. If the fluid pressure exceeds the required level, then the excess fluid

returns back to the reservoir and remains there until the pressure acquires the required

level.

Cylinder movement is controlled by a three-position change over a control valve.

When the piston of the valve is changed to upper position, the pipe pressure line is

connected to port A and thus the load is raised.

When the position of the valve is changed to lower position, the pipe pressure line is

connected to port B and thus the load is lowered.

When the valve is at center position, it locks the fluid into the cylinder(thereby

holding it in position) and dead-ends the fluid line (causing all the pump output fluid to return

to tank via the pressure relief).

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In industry, a machine designer conveys the design of hydraulic systems using a circuit

diagram. Figure shows the components of the hydraulic system using symbols. The working

fluid, which is the hydraulic oil, is stored in a reservoir. When the electric motor is switched

ON, it runs a positive displacement pump that draws hydraulic oil through a filter and delivers

at high pressure. The pressurized oil passes through the regulating valve and does work on

actuator. Oil from the other end of the actuator goes back to the tank via return line. To and fro

motion of the cylinder is controlled using directional control valve.

Cylinder Extended

Retract

Motor Directional control valve

Pump

Pressure regulator

Filter

Breather

Reservoir

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6.4 Basic Components of a Pneumatic System:

The functions of various components shown in Fig.are as follows:

The pneumatic actuator converts the fluid power into mechanical power to

perform useful work.

The compressor is used to compress the fresh air drawn from the atmosphere.

The storage reservoir is used to store a given volume of compressed air.

The valves are used to control the direction, flow rate and pressure of compressed

air.

External power supply (motor) is used to drive the compressor.

The piping system carries the pressurized air from one location to another.

Air is drawn from the atmosphere through an air filter and raised to required pressure by an air

compressor. As the pressure rises, the temperature also rises; hence, an air cooler is provided to

cool the air with some preliminary treatment to remove the moisture. The treated pressurized air

then needs to get stored to maintain the pressure. With the storage reservoir, a pressure switch is

fitted to start and stop the electric motor when pressure falls and reaches the required level

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6.5 Comparison between Hydraulic and Pneumatic Systems:

Usually hydraulic and pneumatic systems and equipment do not compete. They are so dissimilar

that there are few problems in selecting any of them that cannot be readily resolved. Certainly,

availability is one of the important factors of selection but this may be outweighed by other

factors. In numerous instances, for example, air is preferred to meet certain unalterable

conditions, that is, in“hot spots” where there is an open furnace or other potential ignition hazard

or in operations where motion is required at extremely high speeds. It is often found more

efficient to use a combined circuit in which oil is used in one part and air in another on the same

machine or process. Table 1.2 shows a brief comparison of hydraulic and pneumatic systems.

Table :Comparison between a hydraulic and a pneumatic system</table>

S. No. Hydraulic System

Pneumatic

System

It employs a pressurized liquid It employs a compressed gas, usually

1.

air, as a fluid

as a fluid

2.

An oil hydraulic system operates at A pneumatic system usually operates

pressures up to 700 bar at 5–10 bar

3. Generally designed as closed system Usually designed as open system

4.

The system slows down when leakage Leakage does not

affect the system

occurs much

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5. Valve operations are difficult Valve operations are easy

6. Heavier in weight Lighter in weight

Pumps are used to provide Compressors are used to provide

7. compressed

gases

pressurized liquids

8. The system is unsafe to fire hazards The system is free from fire hazards

9.

Automatic lubrication is provided Special arrangements for lubrication

are needed

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Objective Type Questions

Fill in the Blanks

1.Fluid power is the technology that deals with the generation………and transmission of

forces and movement of mechanical elements or systems.

2.The main objective of fluid transport systems is to deliver a fluid from one location to

another, whereas fluid power systems are designed to perform…….. .

3.There are three basic methods of transmitting power: Electrical, mechanical and ……

.

4.Only ………..are capable of providing constant force or torque regardless of speed

changes.

5.The weight-to-power ratio of a hydraulic system is comparatively………than that of an

electromechanical system.

State True or False

1. Hydraulic lines can burst and pose serious problems.

2. Power losses and leakages are less in pneumatic systems.

3. Pneumatic system is not free from fire hazards.

4. Hydraulic power is especially useful when performing heavy work.

5. Water is a good functional hydraulic fluid.

Review Questions:

1. Define the term fluid power.

2. Differentiate between fluid transport and fluid power systems.

3. Differentiate between hydraulics and pneumatics.

4. List the six basic components used in a hydraulic system.

5. List the six basic components used in a pneumatic system.

6. List 10 applications of fluid power in the automotive industry.

7. Name 10 hydraulic applications and 10 pneumatic applications.

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8. List five advantages and five disadvantages of hydraulics.

9. List five advantages and five disadvantages of pneumatics.

10. List the main components of a fluid power system and their functions.

11. Discuss in detail the future of fluid power industry in India.

12. Compare different power systems used in industries.

13. What is the main difference between an open-loop and a closed-loop fluid power system?

14. List five major manufactures of fluid power equipment and systems in India.

15. List five major manufactures of fluid power equipment and systems in the world.

16. Visit any industry nearby and list the hydraulic/pneumatic parts or systems used and their

purposes.

17. Why is the hydraulic power especially useful when performing heavy work?

18. Differentiate between oil hydraulics and pneumatics.

19. List any five applications of fluid power systems.

20 List the main components of a fluid power system and their functions.

Answers:

Fill in the Blanks

1. Control

2. Work

3. Fluid power

4. Fluid power systems

5. Less

State True or False

1. True

2. True

3. False

4. True

5. False