SJP POLYTECHNIC DAMLA

Branch – Mechanical Engineering

Semester – 4th

Subject – Hydraulics and Pneumatics

Code – 171741

Chapter-1 (INTRODUCTION)

Fluid

A Fluid is a substance which continuously deforms under the effect of shear stress.

OR

Fluid is a substance which does not resist a shear stress and deforms under it. It has

no definite shape but takes the shape of containing vessel. Its shape changes when

the shearing force is applied over. It flows, therefore under the effect of the

shearing force.

Examples of fluids are: water, oil, air, gases and vapours etc.

CLASSIFICATION OF FLUIDS:

Fluids are broadly classified in following two categories:

1. Liquids

2. Gases or Vapour

TYPES OF FLUIDS

The fluids may be classified into the following types:

[1] Ideal fluid

[2] Real fluid

[3] Newtonian fluid

[4] Non-Newtonian fluid

[5] Ideal plastic fluid

[6] Thixotropic substance.

Ideal Fluid

A fluid, which is incompressible, has no viscosity and no shearing resistance is

known as an ideal fluid or perfect fluid. Such fluids do not exist in nature and are,

therefore, only imaginary fluids, as all the fluids which exist, have some viscosity.

Real Fluids

Fluids which possess the properties such as viscosity, surface tension

and compressibility are referred as real or practical fluids.

All the fluids, in actual practice, are real fluids.

Newtonian Fluids

Fluid which do not obey the Newton’s law of viscosity is known as non-

Newtonian fluids.

OR

A real fluid in which the shear stress is not proportional to the rate of shear strain

is known as a non-Newtonian fluid.

Ideal Plastic Fluid Or Bingham Fluid

A fluid, in which shear stress is more than the yield value and proportional to the

rate of shear strain is known as ideal plastic fluid or Bingham fluid.

Thixotropic Substance

A substance, which is a non-Newtonian fluid, has a non-linear relationship

between the shear stress and the rate of angular deformation, beyond an initial

yield stress is called thixotropic substance.

HYDRAULICS

Hydraulics is that branch of engineering science which is based on experimental

observation of water flow.

CONCEPT OF CONTINUUM

A continuous and homogenous fluid medium is called continuum.

PROPERTIES OF FLUIDS

Density or Mass Density

Weight Density or Specific Weight

Specific Volume

Specific Gravity

Viscosity

Kinematic Viscosity

Surface Tension

DENSITY OR MASS DENSITY

Density of fluid is defined as the ratio of mass of fluid to its volume.

WEIGHT DENSITY OR SPECIFIC WEIGHT

Weight density or specific weight of fluid is defined as the weight per unit volume.

SPECIFIC VOLUME

Specific volume of a fluid is defined as the volume per unit mass of fluid.

SPECIFIC GRAVITY

Specific gravity is defined as the ratio of specific weight (or mass density) of the

fluid to the specific weight of standard fluid (or mass density of standard fluid).

VISCOSITY

Viscosity of fluid is defined as to be that property of fluid which determines its

resistance to shearing stress or shear deformation or angular deformation.

ADHESION

The property of a liquid which enables it to adhere to another body with which it

comes into contact is called adhesion.

Chapter-2 (PRESSURE AND ITS MEASUREMENT)

ATMOSPHERIC PRESSURE

Atmospheric pressure is the normal pressure exerted by atmospheric air on all

surfaces in contact with it.

GAUGE PRESSURE

If the pressure to be measured by gauge is above atmospheric pressure, it is

called positive gauge pressure.

Gauge pressure is defined as the pressure which is measured with the help of

pressure measuring instrument, in which the atmospheric pressure is taken as

datum i.e. atmospheric pressure on scale is marked as zero.

VACUUM PRESSURE

When pressure to be recorded is below atmosphere, it is called vacuum pressure or

negative pressure this indicates the amount by which the recorded pressure is

below atmospheric pressure.

ABSOLUTE PRESSURE

Absolute pressure is defined as the pressure measured above absolute zero of

pressure. In other words, a pressure measured in a complete vacuum is called

absolute pressure.

PRESSURE MEASURING DEVICE

[A] Manometer

[B] Mechanical Gauges

MANOMETER

Manometers are of two types:

[1] Simple manometer or Open type manometers.

[2] Differential type of manometers.

SIMPLE MANOMETERS

The manometers which measure pressure at a point in a fluid contained in a

vessel or pipe are called simple manometers.

A simple manometer consists of a glass tube having one of its ends connected to

a point where pressure is to be measured and other end remains open to

atmosphere.

Simple manometers are of following types:

(i) Piezometer Tube

(ii) U-Tube Manometer or Double Column Manometer.

(iii) Micro manometer or Single Colum Manometer

PIEZOETER TUBE

It is the simplest types of manometer. It is directly fitted to the pipe or container.

Rise or height of liquid into the tube gives the pressure head of liquid.

U-TUBE MANOMETER

For measuring large gauge pressure, u-tube manometer is used. U-tube

manometer may be regarded as the modification of piezometer tube. Actually, u-

tube manometer consists of a glass tube bent in u-shape. One end of the tube is

connected to a pipe or container having a fluid (a) whose pressure is to be

measured while the other end is open to atmosphere.

Mechanical gauges

For pressure higher than two atmospheres, mechanical gauges are used in which

the liquid is counter balanced either by spring or dead weight.

Advantages:

1. Mechanical gauges are advantageous in the sense that they are portable.

2. Operation range is wider.

3. Direct reading is obtained. This is not the case with manometer.

4. Mechanical gauges are not fragile like manometer.

Types of mechanical gauges.

There are three types of mechanical gauges:

(i) Bourdon tube pressure gauge.

(ii) Diaphragm pressure gauge.

(iii) Dead weight pressure gauge.

Bourdon tube pressure gauge

Bourdon tube pressure gage is used to measure high as well as low pressures low

pressure measurement tubes, generally, are made of bronze while for high

pressure measurement nickel steel is generally used as tube material. (See figure).

Bourdon tube is a curved, elliptical-shaped, metallic tube. This tube is bent in the

form of segment of a circle and responds to pressure changes when one end of the

tube which is attached to gauge case, is connected to the pressure source, it tends

to expand as the fluid pressure in tube rises. Hence circumferential stress is set up

or we can say, hope tension is set up. As a result, free end of the tube moves. Free

end is connected by suitable levers to Rack which, then, engages with a small

pinion mounted on the same spindle as pointer. Thus, Rack and pinion move.

Pressure is indicated by the pointer over a printed dial.

Chapter-3 (FLOW OF FLUIDS)

TYPES OF FLOW

[1] Steady Flow

[2] Un-Steady Flow

[3] Uniform Flow

[4] Non-Uniform Flow

[5] Compressible Flow

[6] Incompressible Flow

[7] Laminar Flow

[8] Turbulent Flow

[9] Rotational Flow

[10] Irrotational Flow

Steady Flow

The flow in which fluid characteristics (fluid dependent variable) such as

velocity, pressure, density at any given point in the fluid, do not change with

time in the direction of any of the three coordinates is known as steady flow.

Unsteady Flow

When in flow, fluid characteristics such as velocity, temperature, density, pressure etc.

changes with time at a given point, it is called unsteady flow.

Uniform Flow

The flow in which fluid characteristics remain same throughout the flow field

at a given time, is called uniform flow.

Non-Uniform Flow

The flow in which the flow characteristics changes at various points along the

path is called non-uniform flow.

Laminar Flow

Laminar flow is called as that type of flow in which the fluid elements move along

well defined paths or stream lines and all the stream lines are straight and parallel.

Turbulent Flow

The type of flow in which the fluid particles do not move in layers and cross the

path of other particles is called a turbulent flow.

CONTINUITY EQUATION OF FLOW

The equation which represents that the weight of liquid remains same at all

sections provided no liquid is added or subtracted from the flowing liquid is

referred as continuity equation of flow.

BERNOULLI’S THEOREM

Bernoulli’s theorem is, actually, based on certain on certain assumptions these

assumptions are:

1. No work or heat interaction between a fluid element and the surrounding takes

place.

2. Flow is steady and continuous.

3. Fluid is incompressible and there is no friction.

4. The flow is one-dimensional i.e. it is along the stream line.

STATEMENT AND PROOF OF BERNOULLI’S THEOREM

“In a steady, continuous flow of an incompressible and ideal fluid, the sum of

potential head, pressure head and kinetic head along a stream line flow remains

same

VENA CONTRACTA

As a liquid approaches an opening, the liquid particles approaching it move along

converging stream lines. This stream of particles issuing from the orifice is called

jet this jet separates from the wall at the sharp edge and finally converges into a

section of minimum cross-sectional area. This section of minimum cross-sectional

area of a maximum contraction is called Vena contracta.

Chapter-4 (FLOW THROUGH PIPES)

INTRODUCTION

A pipe may be defined as closed conduit carrying a fluid under pressure

GEOMETRICAL TERMINOLOGIES

Depth of flow: depth of flow h is defined at a particular section of a

channels. This is so because it may vary from section to section. Thus,

depth of flow is the vertical distance of the bed of the channel from the

free surface at the section under consideration.

Top breadth: this is the breadth of channel section at the free surface.

The water area, A: The water area is the flow cross-sectional area

PERPENDICULAR TO THE direction of flow.

Wetted perimeter: wetted perimeter is the perimeter of solid boundary

in contact with the liquid. It is denoted by P.

LOSS OF ENERGY (OR HEAD) IN PIPE FLOW

ENERGY OR HEAD LOSSES pipe can be grouped; primarily,

into following categories:

Major energy loss.

Minor energy loss.

Major energy loss: this loss of energy is due to fraction in pipe can

be calculated using following formulae

(i) Darcy-Weishbach formulae

(ii) Chezy’s formulae

Minor energy losses: minor energy losses are attributed to the following

factors:

(i) Sudden expansion or contraction of pipe

(ii) Bend in pipe.

(iii) Pipe fitting or an obstruction in pipe.

HYDRAULIC GRADIENT AND TOTAL ENERGY LINE

Total energy line (T.E.L.) means line or contour obtained on plotting

total head at a section in flow direction while hydraulic gradient

(H.G.L.) means line obtained on plotting pressure head (potential +

pressure head of liquid at a section at against flow distance.

Chapter-5 (HYDRAULIC DEVICES)

INTRODUCTION

Devices which employ fluid or liquid in our case, as a medium for

transmitting a force and power by high pressures are called hydraulic

devices.

These are essentially based on the principle of fluid statics and fluid

kinetics. Hydraulic devices which are being discussed in this chapter

are:

1 Hydraulic ram

2 Hydraulic jack

3 Hydraulic accumulator

4 Hydraulic press

5 Hydraulic lift

HYDRAULIC RAM

Hydraulic ram is a device which can lift a small quantity of water to

a greater height when a large quantity of water is available at a

smaller height without using any external power, be it mechanical or

electrical.

Principle: It utilizes the water hammer principle to raise the pressure

energy of small quantity of water and can also be called an “impulse

pump”.

HYDRAULIC JACK

Hydraulic JACK IS A DEVICE USED TO LIFT HEAVY LOADS.

Principle of this device is Pascal’s law of transmission of pressure by

fluid combined with the operation of force pump.

Fig. shows the cross-section of simple hydraulic jack. It consists of a ram

which can raise the load as desired, a pump; a reservoir and small

cylinder containing plunger. Initially, as the handle is raised, plunger

moves up in its cylinder. At this moment, oil from the reservoir flows out

of hole and underside of plunger. Thereafter, plunger is pushed down

closing the hole through which oil entered into small cylinder, then

pushing the oil through a check valve into the large cylinder. Oil builds

up pressure in large cylinder gradually with each stroke of the pump

rising in the piston and load placed on it.

Hydraulic BREAK

ACCORDING TO METHOD OF actuation brakes are classified as

hydraulic brake, magnetic brake or eddy-current brakes. A hydraulic

braking system has been shown in fig. primarily, a hydraulic breaking

system is a liquid coupling between brake pedal and individual brake

shoe.

Chapter-6 (WATER TURBINES AND PUMPS)

CLASSIFICATION OF TURBINES

Broadly, turbines are classified on following two basis:

Hydraulic action of water or nature of energy head processed by water at

inlet.

Direction of flow of water in the runner or we can say direction of flow

along the vanes

HYDRAULIC ACTION OF WATER OR NATURE OF ENERGY

HEAD

On this basis, turbines are classified as under:

Impulse turbines

Reaction turbines

Impulse Turbines

Those turbine in which runner rotates by impulse action (impact) of

water are called impulse turbines.

Examples of impulse turbines are: Pelton Wheel, Girard Turbine.

Reaction Turbines

Those turbines in which the water entering the runner possesses

pressure as well as kinetic energy are called reaction turbines.

Examples: Francis Turbine, Kaplan Turbine.

CLASSIFICATION ACCORDING TO DIRECTION OF FLOW OF

WATER IN RUNNER

ON THE BASIS OF DIRECTION OF FLOW OF WATER, turbines

are classified as under:

(1) Tangential Flow Turbines

(2) Radial Flow Turbines

Comparison between Impulse and Reaction Turbines

S. No. Impulse Turbine Reaction Turbine

1. The total available head is converted into Only a part of available

velocity head by using a nozzle. head is converted into

velocity head rest of it

being converted into

pressure head. No

separate nozzle is used.

Both pressure and

2. Only the jet velocity changes in the process of velocity changes as fluid

fluid flow. flow through the runner.

Water must be admitted

over the entire

3. Water is admitted over part of circumstance. circumference of the

runner.

Water tight casing is must

Water tight casing is not required as the for enclosing the runner.

4. casing has no hydraulic function to perform

as such. It simply prevents splashing of water

and finally leads the water to tail race. It may be installed both

Turbine is always installed above tail race. above and below tail race.

Draft tube is used.

5. No draft tube is used. Air runner wheel always

Air has free access to vanes as the wheel run full.

does not run full.

Pelton Turbine

Invented by Pelton in 1890.

The Pelton turbine is a tangential flow impulse turbine.

The Pelton wheel is most efficient in high head applications.

Power plants with net heads ranging from 200 to 1,500 m.

The largest units can be up to 200 Megawatts.

Pelton turbines are best suited for high head and low flow sites.

Depending on water flow and design, Pelton wheels can operate with heads as

small as 15 meters and as high as 1800 meters.

As the height of fall increases, less volume of water can generate same power.

Horizontal arrangement is found only in medium and small sized turbines

with usually one or two jets. In some designs, up to four jets have been used.

The flow passes through the inlet bend to the nozzle outlet, where it flows out as a

compact jet through atmospheric air on to the wheel buckets. From the outlet of the

buckets the water falls through the pit down into the tail water canal.

Francis Turbine

The Francis turbine is a reaction turbine, which means that the working fluid

changes pressure as it moves through the turbine, giving up its energy.

The inlet is spiral shaped. The guide vanes direct the water tangentially to the

runner causing the runner to spin.

The guide vanes (or wicket gate) may be adjustable to allow efficient turbine

operation for a range of water flow conditions.

Power plants with net heads ranging from 20 to 750 m.

Draft Tube

In a reaction turbine, water leaves the runner with remaining kinetic energy. To

recover as much of this energy as possible, the runner outlet is connected to a

diffuser, called draft tube. The draft tube converts the dynamic pressure (kinetic

energy) into static pressure.

Draft tube permits a suction head to be established at the runner exit, thus making

it possible for placing the wheel and connecting machinery at a level above that of

water in the tail race under high water flow conditions of river, without loss of

head.

To operate properly, reaction turbines must have a submerged discharge.

The water after passing through the runner enters the draft tube, which directs the

water to the point of discharge.

The aim of the draft tube is also to convert the main part of the kinetic energy at

the runner outlet to pressure energy at the draft tube outlet.

Cavitation

Cavitation is a term used to describe a process, which includes nucleation, growth

and implosion of vapour or gas filled cavities. These cavities are formed into a

liquid when the static pressure of the liquid for one reason or another is reduced

below its vapour pressure at the prevailing temperature. When cavities are carried

to high-pressure region, they implode violently.

Cavitation is an undesirable effect that results in pitting, mechanical vibration and

loss of efficiency.

If the nozzle and buckets are not properly shaped in impulse turbines, flow

separation from the boundaries may occur at some operating conditions that may

cause regions of low pressure and result in cavitation.

The turbine parts exposed to cavitation are the runners, draft tube cones for the

Francis and Kaplan turbines and the needles, nozzles and the runner buckets of the

Pelton turbines.

Measures for combating erosion and damage under cavitation conditions include

improvements in hydraulic design and production of components with erosion

resistant materials and arrangement of the turbines for operations within good

range of acceptable cavitation conditions.

Specific Speed

It is defined as the speed of a turbine which is identical in shape, geometrical

dimensions, blade angles, gate opening etc., with the actual turbine but of such a

size that it will develop unit power when working under unit head

This is the speed at which the runner of a particular diameter will develop 1 kW (1

hp) power under 1 m (1 ft) head.

Ns = N 5P

H 4

The specific speed is an important factor governing the selection of the type of

runner best suited for a given operating range. The impulse (Pelton) turbines have

very low specific speeds relative to Kaplan turbines. The specific speed of a

Francis turbine lies between the impulse and Kaplan turbine.

Selection of Turbines

Turbine Head Specific Speed

(SI)

Pelton Wheel >300 m 8.5-30 (Single Jet)

30-51 (2 or More)

Francis Turbine 50-450 m 51-255

Kaplan Turbine Up to 60 m 255-860

Hydraulic pump

Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or

hydrodynamic. A hydraulic pump is a mechanical source of power that converts

mechanical power into hydraulic energy (hydrostatic energy i.e. flow, pressure). It

generates flow with enough power to overcome pressure induced by the load at the

pump outlet. When a hydraulic pump operates, it creates a vacuum at the pump

inlet, which forces liquid from the reservoir into the inlet line to the pump and by

mechanical action delivers this liquid to the pump outlet and forces it into the

hydraulic system. Hydrostatic pumps are positive displacement pumps while

hydrodynamic pumps can be fixed displacement pumps, in which the displacement

(flow through the pump per rotation of the pump) cannot be adjusted, or variable

displacement pumps, which have a more complicated construction that allows the

displacement to be adjusted. Hydrodynamic pumps are more frequent in day-to-

day life. Hydrostatic pumps of various types all work on the principle of Pascal's

law.

Gear pumps

These pumps create pressure through the meshing of the gear teeth, which forces

fluid around the gears to pressurize the outlet side. For lubrication, the gear pump

uses a small amount of oil from the pressurized side of the gears, bleeds this

through the (typically) hydrodynamic bearings, and vents the same oil either to the

low pressure side of the gears, or through a dedicated drain port on the pump

housing. Some gear pumps can be quite noisy, compared to other types, but

modern gear pumps are highly reliable and much quieter than older models. This is

in part due to designs incorporating split gears, helical gear teeth and higher

precision/quality tooth profiles that mesh and un mesh more smoothly, reducing

pressure ripple and related detrimental problems. Another positive attribute of the

gear pump, is that catastrophic breakdown is a lot less common than in most other

types of hydraulic pumps. This is because the gears gradually wear down the

housing and/or main bushings, reducing the volumetric efficiency of the pump

gradually until it is all but useless. This often happens long before wear causes the

unit to seize or break down.

Rotary vane pumps

Rotary vane pumps (fixed and simple adjustable displacement) have higher

efficiencies than gear pumps, but are also used for mid pressures up to 180 bar

(18,000 kPa) in general. Modern units can exceed 300 bar (30,000 kPa) in

continuous operation, although vane pumps are not regarded as "high pressure"

components. Some types of vane pumps can change the centre of the vane body, so

that a simple adjustable pump is obtained. These adjustable vane pumps are in

general constant pressure or constant power pumps: the displacement is increased

until the required pressure or power is reached and subsequently the displacement

or swept volume is decreased until an equilibrium is reached. A critical element in

vane pump design is how the vanes are pushed into contact with the pump housing,

and how the vane tips are machined at this very point. Several type of "lip" designs

are used, and the main objective is to provide a tight seal between the inside of the

housing and the vane, and at the same time to minimize wear and metal-to-metal

contact. Forcing the vane out of the rotating centre and towards the pump housing

is accomplished using spring-loaded vanes, or more traditionally, vanes loaded

hydrodynamically.

Screw pumps

Principle of screw pump

Screw pumps (fixed displacement) consist of two Archimedes' screws that

intermesh and are enclosed within the same chamber. These pumps are used for

high flows at relatively low pressure (max 100 bars (10,000 kPa). They were used

on board ships where a constant pressure hydraulic system extended through the

whole ship, especially to control ball valves but also to help drive the steering gear

and other systems. The advantage of the screw pumps is the low sound level of

these pumps; however, the efficiency is not high.

The major problem of screw pumps is that the hydraulic reaction force is

transmitted in a direction that's axially opposed to the direction of the flow.

There are two ways to overcome this problem:

1. put a thrust bearing beneath each rotor;

2. create a hydraulic balance by directing a hydraulic force to a piston under

the rotor.

Types of screw pumps:

1. single end

2. double end

3. single rotor

4. multi rotor timed

5. multi rotor untimed.

Reciprocating pump

A reciprocating pump is a class of positive-displacement pumps which includes

the piston pump, plunger pump and diaphragm pump. When well maintained,

reciprocating pumps will last for years or even decades; however, left untouched,

they can undergo rigorous wear and tear. It is often used where a relatively small

quantity of liquid is to be handled and where delivery pressure is quite large. In

reciprocating pumps, the chamber in which the liquid is trapped, is a stationary

cylinder that contains the piston or plunger

Centrifugal pumps

These are a sub-class of dynamic ax symmetric work-absorbing turbo

machinery. Centrifugal pumps are used to transport fluids by the conversion of

rotational kinetic energy to the hydrodynamic energy of the fluid flow. The

rotational energy typically comes from an engine or electric motor. The fluid enters

the pump impeller along or near to the rotating axis and is accelerated by the

impeller, flowing

radially outward into a diffuser or volute chamber (casing), from which it exits.

Common uses include water, sewage, agriculture, petroleum and petrochemical

pumping. Centrifugal pumps are often chosen for their high flow rate capabilities,

abrasive solution compatibility, mixing potential, as well as their relatively simple

engineering. A centrifugal fan is commonly used to implement a vacuum cleaner.

The reverse function of the centrifugal pump is a water turbine converting potential

energy of water pressure into mechanical rotational energy.

Priming

If the pump casing becomes filled with vapors or gases, the pump impeller

becomes gas-bound and incapable of pumping. To ensure that a centrifugal pump

remains primed and does not become gas-bound, most centrifugal pumps are

located below the level of the source from which the pump is to take its suction.

The same effect can be gained by supplying liquid to the pump suction under

pressure supplied by another pump placed in the suction line.