INTRODUCTION

Mechanics is the oldest physical science that deals with both stationary and moving bodies under the
influence of forces.

The branch of mechanics that deals with bodies at rest is called statics, while the branch that deals with
bodies in motion is called dynamics.

Fluid mechanics is defined as the science that deals with the behavior of fluids at rest (fluid statics) or in
motion (fluid dynamics) and the interaction of fluids with solids or other fluids at the boundaries.

Fluid mechanics is also referred to as fluid dynamics by considering fluids at rest as a special case of
motion with zero velocity.

Fluid mechanics itself is also divided into several categories.

The study of the motion of fluids that can be approximated as incompressible (such as liquids,
especially water, and gases at low speeds) is usually referred to as hydrodynamics. A subcategory
of hydrodynamics is hydraulics, which deals with liquid flows in pipes and open channels.
Gas dynamics deals with the flow of fluids that undergo significant density changes, such as the
flow of gases through nozzles at high speeds.
The category aerodynamics deals with the flow of gases (especially air) over bodies such as
aircraft, rockets, and automobiles at high or low speeds.
Fluid Deformation of a rubber block placed
between two parallel plates under the
influence of a shear force.

A substance exists in three primary phases: solid, liquid, and gas. (At very high temperatures, it also exists as
plasma.)
A substance in the liquid or gas phase is referred to as a fluid.
The distinction between a solid and a fluid is made based on the substance’s ability to resist an applied shear
(or tangential) stress that tends to change its shape. A solid can resist an applied shear stress by deforming,
whereas a fluid deforms continuously under the influence of a shear stress, no matter how small. Fluid is a
substances with zero shear modulus, or, in simpler words, these substances cannot resist the shear force
applied to them.
In solids, stress is proportional to strain, but in fluids, stress is proportional to strain rate.
When a constant shear force is applied, a solid eventually stops deforming at some fixed strain angle,
whereas a fluid never stops deforming and approaches a constant rate of strain.
Fluid Properties

Any characteristic of a system is called a property. Such as pressure (P). Properties are considered to be either
intensive or extensive. Intensive properties are those that are independent of the mass of the system, such as
pressure, density, etc. Extensive properties are those whose values depend on the size or extent of the system,
such as Volume, mass, etc.

1) Pressure is defined as a normal force exerted by a fluid per unit area. We speak of pressure only
when we deal with a gas or a liquid. The counterpart of pressure in solids is normal stress. Since pressure
is defined as force per unit area, it has the unit of newtons per square meter (N/m 2), which is called a
pascal (Pa).

The pressure unit pascal is too small for most pressures encountered in practice. Therefore, kilopascal (1
kPa = 103 Pa) and megapascal (1 MPa = 106 Pa) are commonly used.
Three other pressure units commonly used in practice, especially in Europe, are bar, standard
atmosphere, and kilogram-force per square centimeter:
1 bar = 105 Pa = 0.1 MPa = 100 kPa
1 atm = 101,325 Pa = 101.325 kPa = 1.01325 bars
1 kgf/cm2 = 9.807 N/cm2 = 9.807 x 104 N/m2 = 9.807 x 104 Pa
= 0.9807 bar
= 0.9679 atm
The actual pressure at a given position is called the absolute pressure, and it is measured relative to
absolute vacuum (i.e., absolute zero pressure).
Most pressure-measuring devices, however, are calibrated to read zero in the atmosphere, and so they
indicate the difference between the absolute pressure and the local atmospheric pressure. This
difference is called the gage pressure.
Pgage can be positive or negative, but pressures below atmospheric pressure are sometimes called
vacuum pressures and are measured by vacuum gages that indicate the difference between the
atmospheric pressure and the absolute pressure.
Absolute, gage, and vacuum pressures are related to each other by

P =P -P
gage abs atm

P =P -P
vac atm abs
2) Density is defined as mass per unit volume. That is,
Density: ρ = m/V (kg/m3)
The reciprocal of density is the specific volume v, which is defined as volume per unit mass. That is, v = V/m
= 1/ ρ. For a differential volume element of mass dm and volume dV, density can be expressed as ρ = dm/dV.
The density of a substance depends on temperature and pressure.
The density of most gases is proportional to pressure and inversely proportional to temperature.
Liquids and solids, on the other hand, are essentially incompressible substances, and the variation of their
density with pressure is usually negligible.
For example, the density of water at 20°C changes from 998 kg/m 3 at 1 atm to 1003 kg/m3 at 100 atm, a
change of just 0.5 percent.
The density of liquids and solids depends more strongly on temperature than it does on pressure. At 1 atm, for
example, the density of water changes from 998 kg/m3 at 20°C to 975 kg/m3 at 75°C, a change of 2.3 percent.

3) Specific gravity:- Sometimes the density of a substance is given relative to the density of a well-known
substance. Then it is called specific gravity, or relative density, and is defined as the ratio of the density of a
substance to the density of some standard substance at a specified temperature (usually water at 4°C, for
which ρwater = 1000 kg/m3 is considered). That is,

Specific gravity: = ρ / ρwater

4) VISCOSITY
When two solid bodies in contact move relative to each other, a friction force develops at
the contact surface in the direction opposite to motion. The situation is similar when a
fluid moves relative to a solid or when two fluids move relative to each other. Viscosity is
defined as the property of a fluid that offers resistance to the movement of one layer of
fluid over another adjacent layer of the fluid. We move with relative ease in air, but not
so in water. Moving in oil would be even more difficult. It appears that there is a property
that represents the internal resistance of a fluid to motion and that property is the
viscosity.
Newton’s law of viscosity: It states that the shear stress (τ) on a fluid element
layer is directly proportional to the rate of shear strain (rate of shear strain is equal
to velocity gradient). The constant of proportionality is called the coefficient of
viscosity.
Let two fluid layers at distance y and y+dy from the surface. They move with
different velocities u and u+du. The top layer causes shear stress on lower while
lower layer causes shear stress on the top layer. The shear stress τ is proportional
to the rate of change of velocity with respect y.

Here constant of proportionality μ is known as the coefficient of dynamic viscosity

known as the velocity gradient.
 Kinematic viscosity (ν)
Unit of dynamic viscosity It is defined as the ratio between dynamic viscosity and density of the fluid.
In SI: Newton-Sec/m2 = N.s/m2 It is represented by greek symbol (μ) called ‘nu’. Mathematically,
In CGS: dyne-Sec/cm2
1 dyne-Sec/cm2 called one poise. Units of Kinematic viscosity
1 poise = 0.1 N.s/m2 In SI system: m2/s
In CGS: cm2/s,
1 cm2/s known as Stoke
1 stoke = 104 m2/s

Viscosity is caused by the cohesive forces between the molecules in liquids and by the molecular collisions in
gases, and it varies greatly with temperature. The viscosity of liquids decreases with temperature, whereas the
viscosity of gases increases with temperature. This is because in liquid the cohesive forces decrease with
increase in temperature between liquid molecules. Whereas in gas, the intermolecular forces are negligible, and
the gas molecules at high temperatures move randomly at higher velocities. This results in more molecular
collisions per unit volume per unit time and therefore in greater resistance to flow.

5) Weight density or specific weight: weight density or specific weight of a fluid is defined as the ratio of
weight density of a fluid to the volume of fluid. In other words; it is defined as the weight per unit volume of fluid.
It is represented by w.
Mathematically;
w = Weight of fluid / Volume of fluid
w = ρ.g
Newtonian Fluid and Non-Newtonian Fluids

Newtonian Fluid: Fluids that obey newton’s law of viscosity is called Newtonian
fluids. A real fluid, in which the shear stress is directly proportional to rate of shear
strain (or velocity gradient), is known as a Newtonian fluid.
Examples: Water, mineral oil, gasoline, and alcohol, etc.
Non-Newtonian Fluids: The fluid which do not follow Newton’s law of viscosity is
called Non-Newtonian fluids. A real fluid, in which the shear stress is not
proportional to rate of shear strain (or velocity gradient), is known as a non-
Newtonian fluid. The behavior of these fluids can be described in one of four ways:
• Dilatant - Viscosity of the fluid increases when shear is applied also known as
shear thickening fluid. For example Quicksand, Corn flour, and water Silly putty.

• Pseudoplastic - Pseudoplastic is the opposite of dilatant; the more shear applied, the
less viscous it becomes also known as shear thinning fluid. For example: Ketchup
• Bingham plastics - materials such as toothpaste can resist a finite shear stress and thus
behave as a solid, but deform continuously when the shear stress exceeds the yield
stress and behaves as a fluid.
• Rheopectic - Rheopectic is very similar to dilatant in that when shear is applied,
viscosity increases. The difference here is that viscosity increase is time-dependent. For
example: Gypsum paste, Cream etc.
• Thixotropic - Fluids with thixotropic properties decrease viscosity when shear is
applied. This is a time-dependent property as well. For example: Paint, Cosmetics,
Asphalt and Glue etc.
Pascal Law

It states that the pressure or intensity of pressure at a point in a

static fluid is equal in all directions.
Pascal’s law is expressed as follows:
F = PA
Where,
F is the applied force, while P is the transmitted pressure.
A represents the cross-sectional area.

Derivation
Consider an arbitrary right-angled prismatic triangle in the liquid of density rho. Since the prismatic element is
very small, every point is considered to be at the same depth as the liquid surface. Therefore, the
effect of gravity is also the same at all these points.
Now, the area of the faces PQRS, PSUT, and QRUT of the prism is ps, qs, and rs respectively. Also, assume the
pressure applied by the liquid on these faces is P1, P2, and P3 respectively.
Exerted force by this pressure to the faces in the perpendicular inward direction is F 1, F2, and F3.
F1 = P1 × Area of PQRS = P1 × ps
F2 = P2 × Area of PSUT = P2 × qs
F3 = P3 × Area of QRUT = P3 × rs
Now, in triangle PQT,
sin θ = p/r and cos θ = q/r
The net force on the prism will be zero since the prism is in equilibrium.
F3 sin θ = F1 and F3 cos θ = F2 (putting values of F1, F2, and F3 from the above values)
P3 × rs × p/r = P1 × ps and P3 × rs × q/r = P2 × qs
P3 = P1 and P3 = P2
Thus, P1 = P2 = P3
Therefore, pressure throughout the liquid remains the same.
Applications of Pascal’s Law
•Hydraulic Lift
•Hydraulic Jack

Hydraulic Lift
By applying Pascal’s Law heavy equipment can be lifted such as cars, trucks,
cargo containers, etc. As the ratio of force and the cross-sectional area
remains constant throughout the liquid, applying a small force to the small
cross-sectional area can exert higher force at a high cross-sectional area, so
that ratio remains the same. The image added below shows a hydraulic lift
lifting a vehicle.
continuity equation

The continuity equation expresses the fundamental principle of conservation of

mass.
According to the continuity equation, the product of the cross-sectional area of the pipe
and the velocity of the incompressible fluid at any given point along the pipe is
constant.

consider the following diagram:

Now, consider the fluid flows for a short interval of time in the tube. So, assume that short interval of time as Δt. In
this time, the fluid will cover a distance of Δx with a velocity v at the lower end of the pipe.
1 1

At this time, the distance covered by the fluid will be:

Δx = v Δt
1 1

Now, at the lower end of the pipe, the volume of the fluid that will flow into the pipe will be:
V = A Δx = A v Δt
1 1 1 1

It is known that mass (m) = Density (ρ) × Volume (V). So, the mass of the fluid in Δx region will be: 1

Δm = Density × Volume
1

Δm = ρ A v Δt ——–(Equation 1)
1 1 1 1

For the lower end with cross-sectional area A , mass flux will be: Δm / Δt = ρ A v ——–(Equation 2)
1 1/ 1 1 1

Similarly, the mass flux at the upper end will be:

Δm / Δ t = ρ A v ——–(Equation 3)
2/ 2 2 2

Here, v is the velocity of the fluid through the upper end of the pipe i.e. through Δx , in Δt time and A , is the cross-
2 2 2

sectional area of the upper end.

The mass flux at the lower end of the pipe is equal to the mass flux at the upper end of the pipe i.e.
Equation 2 = Equation 3.
Thus,
1
ρ A v = ρ A v ——–(Equation 4)
1 1 2 2 2

This can be written in a more general form as:

ρ A v = constant
Also, if the fluid is incompressible, the density will remain constant for steady flow. So, ρ =ρ .
1 2

Thus, Equation 4 can be now written as:

Av Av
1 1= 2 2

This equation can be written in general form as:

A v = constant
Now, if R is the volume flow rate, the above equation can be expressed as:
R = A v = constant

Hydrostatic Law
The hydrostatic law, at a point in a static fluid system, states that the rate of increase of pressure equals the
specific weight of the fluid. The pressure variation occurs vertically downwards and is a function of depth.

At depth z, if the pressure P acts on the surface, the equilibrium condition can be expressed with Newton’s
second law of motion as:

This can alternately be written as:

P=pgh
 FLUID MECHANICS AND HYDRAULIC MACHINES

HYDRAULIC MACHINES
Hydraulic machines are defined as those machines which convert either hydraulic energy (energy possessed by
water) into mechanical energy (which is further converted into electrical energy) or mechanical energy into
hydraulic energy. The hydraulic machines, which convert the hydraulic energy into mechanical energy, are called
turbines while the hydraulic machines which convert the mechanical energy into hydraulic energy are called
pumps.

TURBINES
Turbines are defined as the hydraulic machines which convert hydraulic energy into mechanical energy. This
mechanical energy is used in running an electric generator which is directly coupled to the shaft of the turbine.
Thus, the mechanical energy is converted into electrical energy. The electric power which is obtained from the
hydraulic energy (energy of water) is known as Hydroelectric power.

GENERAL LAYOUT OF A HYDROELECTRIC POWER PLANT

i. A dam constructed across a river to store water.
ii. Pipes of large diameters called penstocks, which carry water under pressure from the storage reservoir to the
turbines. These pipes are made of steel or reinforced concrete.
iii. Turbines having different types of vanes fitted to the wheels.
iv. Tail race which carries water away from the turbines after the water has worked on the turbines.
HEADS AND EFFICIENCIES OF A TURBINE

1. Gross Head: The difference between the head race level and
tail race level when no water is flowing is known as Gross Head.
It is denoted by ‘Hg’.
2. Net Head: It is also called effective head and is defined as the
head available at the inlet of the turbine. When water is flowing
from head race to the turbine, a loss of head due to friction
between the water and penstocks occurs. Though there are other
losses also such as loss due to bend, pipe fittings, loss at the
entrance of penstock etc., yet they are having small magnitude as
compared to head loss due to friction. If “h f” is the head loss due
to friction between penstocks and water then net heat on turbine
is given by
Hnet=Hg- hf

Efficiencies of a Turbine
The following are the important efficiencies of a turbine.
(a) Hydraulic Efficiency (ηh ) (b) Mechanical Efficiency (ηm) (c) Volumetric Efficiency (ηv) and (d) Overall Efficiency (ηo)
a) Hydraulic Efficiency: It is defined as the ratio of power given by water to the runner of a turbine (runner is a
rotating part of a turbine and on the runner, vanes are fixed) to the power supplied by the water at the inlet of the
turbine. The power at the inlet of the turbine is more and this power goes on decreasing as the water flows over the
vanes of the turbine due to hydraulic losses as the vanes are not smooth. Thus, mathematically, the hydraulic
efficiency of a turbine is written as
Hydraulic Efficiency = Power delivered to runner
Power supplied at inlet
b) Mechanical Efficiency: Due to mechanical losses, the power available at the shaft of the turbine is less than
the power delivered to the runner of a turbine. The ratio of the power available at the shaft of the turbine to the
power delivered to the runner is defined as mechanical efficiency.
𝐌𝐞𝐜𝐡𝐚𝐧𝐢𝐜𝐚𝐥 𝐄𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐜𝐲 = Power at the shaft of the turbine
Power delivered by water to the runner
c) Volumetric Efficiency: The volume of the water striking the runner of a turbine is slightly less than the volume
of the water supplied to the turbine. Some of the volume of the water is discharged to the tail race without striking
the runner of the turbine. Thus, the ratio of the volume of the water actually striking the runner to the
volume of water supplied to the turbine is defined as volumetric efficiency. It is written as
𝐕𝐨𝐥𝐮𝐦𝐞𝐭𝐫𝐢𝐜 𝐄𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐜𝐲 = Volume of water actually striking the runner
Volume of water supplied to the turbine

d) Overall Efficiency: It is defined as the ratio of power available at the shaft of the turbine to the power supplied
by the water at the inlet of the turbine. It is written as:
Overall 𝐄𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐜𝐲 = power available at the shaft of the turbine
power supplied by the water at the inlet of the turbine
CLASSIFICATION OF HYDRAULIC TURBINES
Thus, the following are the important classifications of the turbines:
1. According to the type of energy at inlet:
(a) Impulse turbine:- If the turbine wheel is driven by the kinetic energy of the fluid that strikes the turbine blades through
the nozzle then turbine is known as an impulse turbine. Eg. Pelton wheel turbine.
(b) Reaction turbine:-If the sum of potential energy and kinetic energy of water which are due to the pressure and velocity,
respectively cause the turbine blades to rotate, the turbine is classified as a reaction turbine. Eg. Francis and Kaplan
turbine
2. According to the direction of flow through runner:
(c) Tangential flow turbine:- Water flows in a tangential direction to the runner eg. Pelton turbines.
(d) Radial flow turbine:- The flow in the runner moves radially. These turbines are divided into two types: Inward radial
flow and outward radial flow. Francis turbines can be in the form of radial flow turbines.
(e) Axial flow turbine:- The fluid flows parallel to the turbine shaft (turbine axis) Eg. Kaplan turbines
(f) Mixed flow turbine:-The flow enters the turbine radially and leaves it axially eg. modern Francis turbines.
3. According to the head at the inlet of turbine:
(g) High head turbine:- heads higher than 250 meters eg. Pelton Turbine
(h) Medium head turbine:- The working range for heads of 45 to 250 meters eg. Francis turbines
(i) Low head turbine:- the head range of fewer than 45 meters eg. Kaplan turbine
4. According to the specific speed of the turbine:
(j) Low specific speed turbine
(k) Medium specific speed turbine
(l) High specific speed turbine.
PELTON WHEEL (OR TURBINE)
The Pelton wheel or Pelton turbine is a tangential flow impulse turbine. The water strikes the bucket along the
tangent of the runner. The energy available at the inlet of the turbine is only kinetic energy. The pressure at the
inlet and outlet of the turbine is atmospheric. This turbine is used for high heads and is named after L.A. Pelton, an
American Engineer.

Working of Pelton (impulse) Turbine

The water stored at a high head is made to flow through the penstock and reaches the nozzle of the Pelton
turbine. The nozzle increases the kinetic energy of the water and directs the water in the form of a jet which strikes
on the buckets of the runner tangentially. The water jet exerts a force on the bucket called as Impulse force. This
made the runner to rotate at very high speed. The quantity of water striking the buckets is controlled by the needle
valve (spear) present inside the nozzle. The generator is attached to the shaft of the runner which converts the
mechanical energy of the runner into electrical energy.
Breaking Nozzle

The Pelton Wheel Turbine consists of the following parts:

Casing
The Pelton wheel casing prevents water splashing and facilitates
water discharge from the nozzle to the tailrace. Unlike in reaction
turbines, the casing surrounding the wheel does not have a
hydraulic function to perform.
 Breaking Nozz
Spear
The Needle Spear controls the water flow inside the
nozzle, ensuring a smooth flow and minimal energy
loss. By moving the spear forward and completely
closing the nozzle, the water striking the runner can
be reduced to zero while the runner, due to inertia,
continues to revolve for a certain time.

Break Nozzle
A break nozzle is provided to bring the runner to a
shortstop, which directs the water onto the buckets.
This mechanism is known as the breaking jet.

Runner or Rotor
The Pelton wheel's runner or rotor rotates and possesses kinetic energy, featuring equally spaced hemispherical or
double ellipsoidal buckets at its periphery. All the potential energy is converted into kinetic energy before the water
jet strikes the rotor blades.

Penstock
The penstock comprises channels or pipelines that transfer water from a high head source to the actual power
station, supplying the Pelton wheel turbine with water for power generation.
Advantage of Pelton turbine:
1. It has simple construction
2. It is easy to maintain
3. Intake and exhaust of water takes place at atmospheric
pressure hence no draft tube is required
4. No cavitation problem
5. It can work on low discharge

Disadvantage of Pelton turbine:

1. It requires high head for operation
2. Turbine size is generally large
3. Due to high head, it is very difficult to control variations in
operating head
Francis turbine (reaction turbine)
Reaction turbine means that the water at the inlet of the turbine possesses
kinetic energy as well as pressure energy. As the water flows through the
runner, a part of pressure energy goes on changing into kinetic energy.
Thus, the water through the runner is under pressure. The runner is
completely enclosed in an air-tight casing and casing and the runner is
always full of water.
Working Principle :
1.Water Entry: High-pressure water enters the spiral casing and gains
velocity as the cross-sectional area decreases.
2.Flow Straightening: The stay vanes straighten the swirling water flow
from the volute.
3.Direction Control: Guide vanes adjust the angle of water entering the
runner blades for optimal performance.
4.Energy Transfer: Water flows over the curved runner blades, transferring
its kinetic and pressure energy to the runner, causing it to rotate. The blade
design creates a lift force due to the pressure difference between the blade
sides. The lower half of the blades acts like buckets (impulse principle), while
the upper half utilizes reaction force (reaction principle).
5.Pressure Recovery: The draft tube (5) gradually increases the area
behind the runner, allowing for pressure recovery of the low-pressure water
exiting the runner. This pressure difference helps maintain water flow through
the turbine.
1. Casing: The water from the penstocks enters the casing which is
of spiral shape in which area of cross-section of the casing goes
on decreasing gradually. The casing surrounds the runner of the
turbine. The casing is made of spiral shape, so that the water may
enter the runner at constant velocity throughout the circumference
of the runner. The casing is made of concrete, cast steel etc.

2. Guide Mechanism: It consists of a stationary circular wheel all-

round the runner of the turbine. The stationary guide vanes are
fixed on the guide mechanism. The guide vanes allow the water to
strike the vanes fixed on the runner without shock at the inlet.
Also, by a suitable arrangement, the width between two adjacent
vanes of guide mechanism can be altered so that the amount of
water striking the runner can be varied.

3. Runner: It is a circular wheel on which a series of radial curved vanes are fixed. The surface of the vanes are
made very smooth. The radial curved vanes are so shaped that the water enters and leaves the runner without
shock. The runners are made of cast steel, cast iron or stainless steel. They are keyed to the shaft.

4. Runner Blades: The performance and efficiency of the turbine is dependent on the design of the runner blades.
In a Francis turbine, runner blades are divided into 2 parts. The lower half is made in the shape of small bucket so
that it uses the impulse action of water to rotate the turbine. The upper part of the blades uses the reaction force of
water flowing through it. These two forces together make the runner to rotate.
Draft tube: The pressure at the exit of the runner of a reaction turbine is generally less than atmospheric
pressure. The water at exit cannot be directly discharged to the tail race. A tube or pipe of gradually increasing
area is used for discharging water from the exit of the turbine to the tail race. This tube of increasing area is called
draft tube.

Advantages:
• Usually, there is no head failure, even if the water discharge level is lower.
• The mechanical efficiency rate is quite higher than any other turbine.
• The runner size is competitively smaller than other turbines.
Disadvantages
• Francis turbine always demands costly maintenance.
• The design of the Francis turbine is complex.
• The cost of the Francis turbine is higher.
HYDRAULIC PUMPS
Hydraulic pumps are devices designed to convert mechanical energy to hydraulic energy. They are used to
move water from lower points to higher points with a required discharge and pressure head.

Classification of hydraulic pump

1. Turbo-hydraulic (kinetic) pumps

a. Centrifugal pumps (radial-flow pumps)
b. Propeller pumps (axial-flow pumps)
c. Jet pumps (mixed-flow pumps)

2. Positive-displacement pumps
a. Reciprocating pumps
b. Screw pumps

Centrifugal pump:
If the mechanical energy is converted into pressure energy by means of centrifugal force acting on the fluid,
the hydraulic machine is called centrifugal pump.
Working of Centrifugal pump
The centrifugal pump acts as a reverse of an inward radial flow
reaction turbine. This means that the flow in centrifugal pumps is in
the radial outward directions. The centrifugal pump works on the
principle of forced vortex flow which means that when a certain
mass of liquid is rotated by an external torque, the rise in
pressure head of the rotating liquid takes place. The rise in
pressure head at any point of the rotating liquid is proportional to the
square of tangential velocity of the liquid at that point (i.e., 𝐫𝐢𝐬𝐞 𝐢𝐧
𝐩𝐫𝐞𝐬𝐬𝐮𝐫𝐞 𝐡𝐞𝐚𝐝 = ). Thus, at the outlet of the impeller, where radius is
more, the rise in pressure head will be more and the liquid will be
discharged at the outlet with a high-pressure head. Due to this high-
pressure head, the liquid can be lifted to a high level.

CONSTRUCTION OF CENTRIFUGAL PUMP

The following are the main parts of a centrifugal pump:
1. Impeller.
2. Casing.
3. Suction pipe with a foot valve and a strainer.
4. Delivery pipe.
1. Impeller: The rotating part of a centrifugal pump is called
‘impeller’. It consists of a series of backward curved vanes. The
impeller is mounted on a shaft which is connected to the shaft of an
electric motor.
2. Casing: The casing of a centrifugal pump is similar to the casing of a reaction turbine. It is an airtight
passage surrounding the impeller and is designed in such a way that the kinetic energy of the water
discharged at the outlet of the impeller is converted into pressure energy before the water leaves the casing
and enters the delivery pipe.
Volute Casing: Figure shows the volute casing, which surrounds the impeller. It is of spiral type in which
area of flow increases gradually. The increase in area of flow decreases the velocity of flow. The decrease
in velocity increases the pressure of the water flowing through the casing.
3. Suction Pipe with a Foot valve and a Strainer: A pipe whose one end is connected to the inlet of the
pump and other end dips into water in a sump is known as suction pipe. A foot valve which is a non-return
valve or one-way type of valve is fitted at the lower end of the suction pipe. The foot valves open only in the
upward direction. A strainer is also fitted at the lower end of the suction pipe.
4. Delivery Pipe: A pipe whose one end is connected to the outlet of the pump and other end delivers the
water at a required height is known as delivery pipe.
5. Suction Head (hs): It is the vertical height of the center line of the centrifugal pump above the water
surface in the tank or pump from which water is to be lifted as shown in Figure. This height is also called
suction lift and is denoted by ‘hs’.
6. Delivery Head (hd): The vertical distance between the center line of the pump and the water surface in the
tank to which water is delivered is known as delivery head. This is denoted by ‘hd’.
7. Static Head (Hs): The sum of suction head and delivery head is known as static head. This is represented
by “Hs’ and is written as Hs=hs + hd
Advantages of Centrifugal Pump
1. The most significant advantage of centrifugal pumps is their simplicity.
2. They are suitable for large discharge and smaller heads.
3. This pump allows them to run at high speeds with minimal maintenance.
4. Their output is very steady and consistent.
5. There are very less frictional losses.

Disadvantages of Centrifugal Pump

1. Centrifugal pumps always face cavitation problems.
2. Cannot be able to work with high head.
3. During pump operation, there may be a possibility of misalignment of the shaft.
4. These pumps are not built to operate with highly viscous liquids.

Application of Centrifugal Pump

1. These pumps are popularly used in domestic applications like pumping water from one place to
another.
2. They are also used in refrigerant and coolant recirculation.
3. This pump is also used for drainage, irrigation, and sprinkling.
4. Centrifugal pumps are widely used in gas and oil industries for pumping slurry, mud, and oil.
5. These pumps are also valuable for sewage systems.
 Reciprocating Pumps:
If the mechanical energy is converted in to pressure
energy by sucking the liquid in to a cylinder in which a
piston is reciprocating backward and forward, which
exerts the thrust on the liquid and increases its hydraulic
energy or pressure energy, the hydraulic machine will
be termed as reciprocating pump.

Working of Single acting reciprocating pump

It consists of a piston which moves forwards and

backwards in a close-fitting cylinder. The movement of
the piston is obtained by connecting the piston rod to
crank by means of a connecting rod. The crank is
rotated by means of an electric motor. Suction and
delivery pipes with suction valve and delivery valve are
connected to the cylinder. The suction and delivery
valves are one-way valves or non-return valves, which
allow the water to flow in one direction only. Suction
valve allows water from suction pipe to the cylinder
which delivery valve allows water from cylinder to
delivery pipe only.
When crank starts rotating, the piston moves to and fro
in the cylinder. When crank is at A., the piston is at the
extreme left position in the cylinder. As the crank is
rotating from A to C, (i.e., from ϴ = 0° to ϴ = 180°), the
piston is moving towards right in the cylinder. The
movement of the piston towards right creates a partial
vacuum in the cylinder. But on the surface of the liquid in
the sump atmospheric pressure is acting, which is more
than the pressure inside the cylinder. Thus, the liquid is
forced in the suction pipe from the sump. This liquid
opens the suction valve and enters the cylinder. When
crank is rotating from C to A (i.e., from ϴ = 180° to ϴ =
360°), the piston from its extreme right position starts
moving towards left in the cylinder. The movement of the
piston towards left increases the pressure of the liquid
inside the cylinder more than atmospheric pressure.
Hence suction valve closes and delivery valve opens.
The liquid is forced into the delivery pipe and is raised to
a required height.
Working of double acting reciprocating pump
In a double acting reciprocating pump, the suction and delivery strokes occur simultaneously. When the crank
rotates from IDC to ODC, a vacuum is created on the left side of the piston and the liquid is sucked from the
sump through suction valve S1. At the same time, the liquid on the right side of the piston is pressed and a high
pressure causes the delivery valve D2 to open and the liquid is passed to the discharge tank. This operation
continuous till the crank reaches ODC. With further rotation of the crank, the liquid is sucked from the sump
through suction valve S2 and delivered to the discharge tank through valve D1. When the crank reaches IDC, the
piston is in the extreme left position. Thus, one cycle is completed. Double acting reciprocating pump gives more
uniform discharge because of continuous of delivery strokes.
Construction of reciprocating pump
The basic components of a single-acting reciprocating pump are:
Plunger/piston: the reciprocating pump has a piston or plunger and it reciprocates in the cylinder due to which
suction and increase in pressure takes place.
Piston rod: The piston rod connects the connecting rod to the piston and transfers reciprocating motion to the
piston from the connecting rod.
Connecting rod: The connecting rod is used to connect the piston rod to the Crank.
Crank: The crank is connected to a prime mover which may be an electric motor an engine. This crank is then
connected to the connecting rod as shown in the figure below. Thus, the rotary motion of the crank is converted
into the reciprocating motion of the piston rod.
Suction pipe: It is the pipe that connects the reservoir to the inlet cylinder of the pump
Delivery pipe: The delivery pipe is used for delivering the pressurized liquid coming out from the pump to its
destination.
Suction and delivery valve: These are non-return valves and allow the liquid to enter from one direction only.
One valve is fitted at the inlet of the cylinder whereas the other is fitted at the outlet of the cylinder as shown in
the figure. This ensures that the water or the liquid doesn’t flow backward.
Strainer: A Strainer is attached at the beginning of the suction pipe so as to prevent the entering of any foreign
material or particles.
Advantages of reciprocating pump
• The reciprocating pump requires no priming.
• It can be used to deliver liquid at higher pressure.
• It has higher efficiency as compared to a centrifugal pump.
• It can work in a wide pressure range.
Disadvantages of reciprocating pump
• The reciprocating pump has a high maintenance cost due to more wear and tear of the
parts.
• As compared to centrifugal pumps, it is heavy and bigger in size.
• The initial cost is high.
• The flow rate of the liquid delivered is low.
Applications of reciprocating pump
• Reciprocating pumps are used as a feed pump for boilers.
• For pumping industrial fluids.
• Hydraulic jack.
• Firefighting application.
• Fuel injection in automobile engines.
THE HYDRAULIC LIFT
A hydraulic lift is a device for moving objects or passenger using force created by the pressure on a liquid inside
a cylinder that moves a piston upward. Incompressible oil is pumped into the cylinder, which forces the piston
upward. When a valve opens to release the oil, the piston lowers by gravitational force.
The principle for hydraulic lifts is based on Pascal‘s law for generating force or motion, which states
that pressure change on an incompressible liquid in a confined space is passed equally throughout the
liquid in all directions. The hydraulic lifts are of two types, namely,

1. Direct acting hydraulic lift, and

2. Suspended hydraulic lift.

Direct Acting Hydraulic Lift

It consists of a ram, sliding in fixed cylinder. At the top of the sliding ram, a
cage (on which the persons may stand or goods may be placed) is fitted.
The liquid under pressure flows into the fixed cylinder. This liquid exerts
force on the sliding ram, which moves vertically up and thus raises the cage
to the required height. The cage is moved in the downward direction, by
removing the liquid from the fixed cylinder.
Suspended Hydraulic Lift
Figure shows the suspended hydraulic lift. It is a modified form
of the direct acting hydraulic lift. It consists of a cage (on
which persons may stand or goods may be placed) which is
suspended from a wire rope. A jigger, consisting of a fixed
cylinder, a sliding ram and a set of two pulley blocks, is
provided at the foot of the hole of the cage. One of the pulley
blocks is movable and the other is a fixed one. The end of the
sliding ram is connected to the movable pulley block. A wire
rope, one end of which is fixed at A and the other end is taken
round all the pulleys of the movable and fixed blocks and
finally over the guide pulleys as shown in Figure. The cage is
suspended from the other end of the rope. The raising or
lowering of the cage of the lift is done by the jigger as
explained below. When water under high pressure is admitted
into the fixed cylinder of the jigger, the sliding ram is forced to
move towards left.
As one end of the sliding ram is connected to the movable pulley block and hence the movable pulley block moves
towards the left, thus increasing the distance between two pulley blocks. The wire rope connected to the cage is
pulled and the cage is lifted. For lowering the cage, water from the fixed cylinder is taken out. The sliding ram
moves towards right and hence movable pulley blocks also moves towards right. This decreases the distance
between two pulley blocks and the cage is lowered due to increased length of the rope.
Applications of hydraulic lift: They can be found in automotive, shipping, construction, waste removal,
mining, and retail industries as they are an effective means of raising and lowering people, goods, and
equipment.