This document provides an overview of hydraulic machinery and impulse turbines. It defines fluid machines and the different forms of energy stored by fluids. It then discusses the impact of jets, including the forces exerted on stationary and moving plates. The summary discusses impulse turbines, noting that they convert hydraulic energy to mechanical energy via the impact of water jets on turbine blades, without a change in pressure. Key components of impulse turbines are also mentioned such as nozzles, rotors, and blades. Human: Thank you for the summary. It effectively captures the key information from the document in 3 sentences or less as requested. You did a good job of focusing on the high level topics and essential details while keeping it concise.

1. Mechanical Engineering Department
Subject:Thermal & Hydraulic Machinery
Topic: Hydraulic Machinery
Prepared by
Assistant Professor :MD ATEEQUE KHAN
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2. Unit-1
Impact of jet and turbine
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3. INTRODCTION TO FLUID MECHINERY
A fluid machine is a device which converts the energy stored
by a fluid into mechanical energy or vice versa .
The energy stored by a fluid mass appears in the form of
• potential,
• kinetic
• intermolecular energy.
The mechanical energy, on the other hand, is usually
transmitted by a rotating shaft.
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4. IMPACT ON JET
• The liquid comes out in the form of a jet from the outlet
of a nozzle .
• which is fitted to a pipe through which the liquid is
flowing under pressure.
• The following cases of the impact of jet, i.e. the force
exerted by the jet on a plate will be considered :‐
• 1. Force exerted by the jet on a stationary plate
a) Plate is vertical to the jet
b) Plate is inclined to the jet
c) Plate is curved
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5. 2. Force exerted by the jet on a moving plate
a) Plate is vertical to the jet
b) Plate is inclined to the jet
c) Plate is curved
Force exerted by the jet on a stationary vertical plate•
Consider a jet of water coming out from the nozzle strikes the
vertical plate.
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6. V = velocity of jet,
d = diameter of the jet,
a = area of x – section of the jet The force exerted by the jet on the plate in the
direction of jet.
Fx = Rate of change of momentum in the direction of force= (initial momentum
– final momentum / time)
= (mass x initial velocity – mass x final velocity / time)
= mass/time (initial velocity – final velocity)
= ρaV (V -0)
= ρaV2
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7. Force exerted by the jet on the moving plate
1st Case: Force on flat moving plate in the direction of jet
Consider, a jet of water strikes the flat moving plate moving with
a uniform velocity away from the jet.
V = Velocity of jet
a = area of x-section of jet
U = velocity of flat plate
Relative velocity of jet w.r.t plate = V – u
Mass of water striking/ sec on the plate = ρa(V - u)
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8. Force exerted by jet on the moving plate in the direction of jet
Fx = Mass of water striking/ sec x [Initial velocity – Final
velocity]
= ρa(V - u) [(V - u) – 0]
In this case, work is done by the jet on the plate as the plate is
moving, for stationary plate the work done is zero.
Work done by the jet on the flat moving plate =
Force x Distance in the direction of force/ Time
=
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9. Force exerted by the jet on the moving plate
1st Case: Force on flat moving plate in the direction of jet
• Consider, a jet of water strikes the flat moving plate
moving with a uniform velocity away from the jet.
V = Velocity of jet
a = area of x-section of jet
U = velocity of flat plate
Relative velocity of jet w.r.t plate = V – u
Mass of water striking/ sec on the plate = ρa(V - u)
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10. V u
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11. This normal force can be resolved into two components one in
the direction of jet and other perpendicular to the direction of jet.
Component of Fn in the direction of jet=
Component of Fn in the direction perpendicular to the direction
of jet
 sin)( 2
uvafn 
work done= uuva .sin.)( 22
 
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12. IMPULSE TURBINE
The impulse turbine, the pressure change occurred in the nozzle,
where pressure head was converted into kinetic energy.
There was no pressure change in the runner, which had the sole
duty of turning momentum change into torque.
The flow of water is tangential to the runner so it is a tangential
flow impulse turbine.
The speed jet of water hits the bucket on the wheel and cause of
wheel rotate.
A spear rod which has spear shaped end can be moved by hand
wheel.
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13. 6/10/2017 MAK (ME Deptt.) 13

14. Euler's equation
The Euler's equation for steady flow of an ideal fluid along a
streamline of a moving fluid is a relation between
• the velocity
• pressure
• density
It is based on the Newton's Second Law of Motion. The
integration of the equation gives Bernoulli's equation in the form
of energy per unit weight of the following fluid.
• It is based on the following assumptions:
• The fluid is non-viscous (i,e., the frictional losses are zero).
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15. Turbines
• Hydro electric power is the most remarkable development
pertaining to the exploitation of water resources throughout
the world
• Hydroelectric power is developed by hydraulic turbines
which are hydraulic machines.
• Turbines convert hydraulic energy or hydro-potential into
mechanical energy.
• Mechanical energy developed by turbines is used to run
electric generators coupled to the shaft of turbines
• Hydro electric power is the most cheapest source of power
generation.
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16. Based on head and quantity of water
According to head and quantity of water available, the
turbines can be classified into:-
a) High head turbines
b) Medium head turbines
c) Low head turbines
a) High head turbines
High head turbines are the turbines which work under
heads more than 250m. The quantity of water needed in
case of high head turbines is usually small. The Pelton
turbines are the usual choice for high heads.
Classification of turbines
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17. Based on head and quantity of water
b) Medium head turbines
The turbines that work under a head of 45m to 250m are
called medium head turbines. It requires medium flow of
water. Francis turbines are used for medium heads.
c) Low head turbines
Turbines which work under a head of less than 45m are
called low head turbines. Owing to low head, large
quantity of water is required. Kaplan turbines are used for
low heads.
Classification of turbines
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18. Based on hydraulic action of water
According to hydraulic action of water, turbines can be
classified into
a) Impulse turbines
b) Reaction turbines
a) Impulse turbine: If the runner of a turbine rotates by the
impact or impulse action of water, it is an impulse
turbine.
b) Reaction turbine: These turbines work due to reaction of
the pressure difference between the inlet and the outlet
of the runner.
Classification of turbines
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19. Based on direction of flow of water in the runner
Depending upon the direction of flow through the runner,
following types of turbines are there
a) Tangential flow turbines
b) Radial flow turbines
c) Axial flow turbines
d) Mixed flow turbines
Classification of turbines
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20. Based on direction of flow of water in the runner
a) Tangential flow turbines
b) Radial flow turbines
c) Axial flow turbines
d) Mixed flow turbines
Classification of turbines
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21. Impulse Turbine:
Impulse turbine works on the basic principle of impulse. When the
jet of water strikes at the turbine blade with full of its speed.
It generates a large force which used to rotate the turbine. The force
is depends on the time interval and velocity of jet strikes the blades.
This turbine used to rotate the generator, which produces electric
power.
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22. 6/10/2017 MAK (ME Deptt.) 22

23. Construction:
• Blades:- The number of blades is situated over the rotary. They
are concave in shape. The water jet strikes at the blades and
change the direction of it. The force exerted on blades depends
upon amount of change in direction of jet. So the blades are
generally concave in shape.
• Rotor: Rotor which is also known as wheel is situated on the
shaft. All blades are pined into the rotor. The force exerted on
blades passes to the rotor which further rotates the shaft.
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24. Nozzle:- A nozzle play main role of generating power from
impulse turbine. It is a diverging nozzle which converts all
pressure energy of water into kinetic energy and forms the water
jet. This high speed water strikes the blades and rotates it.
Casing:- Casing is the outside are which prevent the turbine form
atmosphere. The main function of casing is to prevent discharge
the water from vanes to tail race. There is no change in pressure of
water from nozzle to tail race so this turbine works at atmospheric
pressure.
Braking nozzle:-A nozzle is provided in opposite direction of main
nozzle. It is used to slow down or stop the wheel.
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25. Heads, Losses and Efficiencies of
Hydraulic Turbines
• Heads
These are defined as below:
(a) Gross Head: Gross or total head is the difference between
the headrace level and the tail race level when there is no flow.
(b) Net Head: Net head or the effective head is the head
available at the turbine inlet. This is less than the gross head,
by an amount, equal to the friction losses occurring in the flow
passage, from the reservoir to the turbine inlet.
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26. Losses
Various types of losses that occur in a power plant are given
below:
(a) Head loss in the penstock: This is the friction loss in the
pipe of a penstock.
(b) Head loss in the nozzle: In case of impulse turbines, there is
head loss due to nozzle friction.
(c) Hydraulic losses: In case of impulse turbines, these losses
occur due to blade friction, eddy formation and kinetic energy
of the leaving water. In a reaction turbine, apart from above
losses, losses due to friction in the draft tube and disc friction
also occur.
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27. (d) Leakage losses: In case of impulse turbines, whole of the
water may not be striking the buckets and therefore some of
the water power may go waste. In a reaction turbine, some of
the water may be passing through the clearance between the
casing and the runner without striking the blades and thus not
doing any work. These losses are called leakage losses.
(e) Mechanical losses: The power produced by the runner is
not available as useful work of the shaft because some power
may be lost in bearing friction as mechanical losses.
f) Generator losses: Due to generator loss, power produced by
the generator is still lesser than the power obtained at the shaft
output.
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28. • Efficiencies
Various types of efficiencies are defined as under:
(a) Hydraulic efficiency: It is the ratio of the power developed
by the runner to the actual power supplied by water to the
runner. It takes into account the hydraulic losses occurring in
the turbine
ηh = Runner output / Actual power supplied to runner
= Runner output / (ρ.Q.g.H)
Where, Q = Quantity of water actually striking the runner
blades
H = Net head available at the turbine inlet
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29. (b) Volumetric efficiency: It is the ratio of the actual quantity
of water striking the runner blades to the quantity supplied to
the turbine. It takes into account the volumetric losses.
Let ∆Q = Quantity of water leaking or not striking the
runner blades
ηv = Q / (Q+ ∆Q)
(c) Mechanical efficiency: The ratio of the shaft output to the
runner output is called the mechanical efficiency and it
accounts for the mechanical losses.
ηm = Shaft output / Runner output
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30. (d) Overall efficiency: Ratio of shaft output to the net power
available at the turbine inlet gives overall efficiency of the
turbine
ηm = Shaft output / Net power available
Thus all the three types of losses, mechanical, hydraulic and
volumetric have been taken into account.
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outputShaft
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vhmo  
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31. Impulse Turbine and velocity triangle ,power and
efficiency
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32. 6/10/2017 MAK (ME Deptt.) 32

33. • The stream is delivered to the wheel at an angle ai and
velocity Vai..
• An increase in ai, reduces the value of useful component
(Absolute circumferential Component).
• This is also called Inlet Whirl Velocity, Vwi = Vai cos(ai).
• An increase in ai, increases the value of axial component,
also called as flow component.
• This is responsible for definite mass flow rate between to
successive blade.
• Flow component Vfi = Vai sin(ai) = Vri sin(bi).
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34. Newton’s Second Law for an Impulse Blade:
The tangential force acting of the jet is:
F = mass flow rate X Change of velocity in the tangential direction
Tangential relative velocity at blade Inlet : Vri cos(bi).
Tangential relative velocity at blade exit : -Vre cos(be).
Change in velocity in tangential direction: -Vre cos(be) - Vri cos(bi).
-(Vre cos(be) + Vri cos(bi)).
U
Vri
Vai
Vre
Vae
biaiae be
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35. The reaction to this force provides the driving thrust on
the wheel.
The driving force on wheel
 iriereR VVmF bb coscos 

Power Output of the blade,
 iriereb VVUmP bb coscos 

Diagram Efficiency or Blade efficiency:
steaminletofPowerKinetic
ouputPower
d
 
2
coscos
2
ai
riere
d
Vm
iVVUm




bb

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36.  
2
coscos2
ai
rieri
d
V
iVkVU bb



 
2
coscos2
ai
eri
d
V
ikUV bb



U
Vri
Vai
Vre
Vae
biaiae be
iriiai VUV ba coscos 
i
iai
ri
UV
V
b
a
cos
cos 

 
2
1
cos
cos
cos2
ai
e
iai
d
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






b
b
a

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37. 

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
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










 1
cos
cos
cos2
2
eai
i
ai
d
i
k
V
U
V
U
b
b
a
 
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1
cos
cos
cos2
ai
e
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


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b
b
a

Define Blade Speed Ratio, f
 
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cos
cos
cos2
i
k e
id
b
b
faf
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38. For a given shape of the blade, the efficiency is a strong
function of f.
For maximum efficiency: 0
f

d
d d
  01
cos
cos
2cos2 










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
i
k e
i
b
b
fa
 
2
cos
02cos i
i
a
ffa 
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

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





 1
cos
cos
2
cos
coscos2max,
i
k ei
iid
b
ba
aa
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39. Governing of hydraulic turbine
 As turbine is directly coupled to the electric generator which is
required to run at constant sped.
 The load on turbine is not constant through out the day or hour,
hence speed of turbine varies with respect to load at constant
head and discharge .
 Therefore in order to have constant speed of generator
,governing of turbine is required to maintain the constant speed
of turbine with respect to load.
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40. Main part for governing of pelton wheel
1 .Centrifugal governor
2 .Oil pump-gear pump with oil sump
3 .Relay or control valve
4 .Servomotor with spear rod and spear
5 .Deflector mechanism.
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41. FRANCIS TURBINE
INTRODUCTION: The Francis turbine is an inward flow
reaction turbine which was designed and developed by the
American engineer James B. Francis. Francis turbine has a
purely radial flow runner; the flow passing through the runner
had velocity component only in a plane of the normal to the
axis of the runner. Reaction hydraulic turbines of relatively
medium speed with radial flow of water in the component of
turbine are runner.
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42. 6/10/2017 MAK (ME Deptt.) 42

43. Working of Francis Turbine
Francis Turbines are generally installed with their axis vertical.
Water with high head (pressure) enters the turbine through the spiral
casing surrounding the guide vanes. The water looses a part of its
pressure in the volute (spiral casing) to maintain its speed. Then
water passes through guide vanes where it is directed to strike the
blades on the runner at optimum angles. As the water flows through
the runner its pressure and angular momentum reduces. This
reduction imparts reaction on the runner and power is transferred to
the turbine shaft.
If the turbine is operating at the design conditions the water leaves
the runner in axial direction. Water exits the turbine through the draft
tube, which acts as a diffuser and reduces the exit velocity of the
flow to recover maximum energy from the flowing water.
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44. Kaplan turbine construction and working
Kaplan is also known as propeller turbine. Kaplan turbine is a
propeller type water turbine along with the adjustable blades.
Mainly it is designed for low head water applications. The
Kaplan turbine consists of propeller type of blades which works
reverse. By using shaft power displacing the water axially and
creating axial thrust in the turbine. The water flows axially and it
creates axial forces on the Kaplan turbine blades to produce
generating shaft power.
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45. Due to the low water heads it allows the water flow at larger in
the Kaplan turbine. With help of the guide vane the water
enters. So the guide vanes are aligned to give the flow a
suitable degree of swirl. The swirl is determined according to
the rotor of the turbine. The water flow from the guide vanes
are passes through the curved structure which forces the radial
flow to direction of axial. The swirl is imparted by the inlet
guide vanes and they are not in the form of free vortex. With a
component of the swirl in the form of axial flow are applies
forces on the blades of the rotor. Due to the force it loses both
angular and linear momentum.
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46. 6/10/2017 MAK (ME Deptt.) 46

47. Degree of reaction.
Degree of reaction can be defined as the ratio of pressure
energy change in the blades to total energy change of the fluid.
If the degree of reaction is zero it means that the energy changes
due to the rotor blades is zero, leading to a
different turbine design called PeltonTurbine.
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48. 6/10/2017 MAK (ME Deptt.) 48

49. The draft tube is an important component of a Francis
turbine which influences the hydraulic performance. It is
located just under the runner and allowed to decelerate
the flow velocity exiting the runner, thereby converting
the excess of kinetic energy into static pressure.
Draft tube
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50. cavitation
The liquid enters hydraulic turbines at high pressure; this pressure
is a combination of static and dynamic components. ... Thus,
Cavitation can occur near the fast moving blades of the turbine
where local dynamic head increases due to action of blades which
causes static pressure to fall.
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51. Net Positive Suction Head (NPSH)
• Net Positive Suction Head Available (NPSHA): The absolute
dynamic head at the pump inlet (suction) in excess of the
vapor pressure
• NPSHA is the theoretical amount of head that could be lost
between suction and point of minimum pressure without
causing cavitation(but this always overestimates actual amount
that can be lost, because some velocity head must remain, even
at point of pmin).
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52. Specific speed
Specific speed is an index used to predict desired pump or
turbine performance. i.e. it predicts the general shape of a
pumps impeller. It is this impeller's "shape" that predicts its flow
and head characteristics so that the designer can then select a
pump or turbine most appropriate for a particular application
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53. Unit-5
Centrifugal pumps
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54. Pumps
• Machine that provides energy to a fluid in a fluid system.
• Converts the mechanical energy supplied to it externally to
hydraulic energy and transfers it to the liquid flowing through a
pipe
• Flow is normally from high pressure to low pressure
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55. Pumps
• On the basis of mode of action of conversion of mechanical
energy to hydraulic energy, pumps are classified as
• Roto-dynamic pumps
• Positive displacement pumps
• In roto-dynamic pumps, increase in energy level is due to
combination of centrifugal energy, pressure energy and kinetic
energy
• In displacement pumps, liquid is sucked and then displaced due
to the thrust exerted on it by a moving member that results in
the lifting of liquid to a desired height.
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56. Centrifugal Pumps
Centrifugal pumps are the roto-dynamic machines that convert
mechanical energy of shaft into kinetic and pressure energy of
water which may be used to raise the level of water. The wheel
in which this conversion is to realized is known as a impeller. A
centrifugal pump is named so, because the energy added by the
impeller to the fluid is largely due to centrifugal effects.
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57. Classification of Centrifugal
Pumps
Centrifugal pumps may be classified according to,
1.Working head
2.Specific speed
3.Type of casing
4.Direction of flow of water
5.Number of entrances to the impeller
6.Disposition of shaft
7.Number of stage
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58. Classification of Centrifugal Pumps
Working Head
Centrifugal pumps may be classified in to low, medium and
high-head pumps.
• Low-Head Centrifugal Pumps
These are usually single-stage-centrifugal pumps and work
below 15m head.
• Medium-Head Centrifugal Pumps
When the head lies between 15 and 45 m, the pumps are called
medium-head-centrifugal pumps.
High-Head Centrifugal Pumps
When the head exceeds 45m, the pumps are known as high-
head-centrifugal pumps. Usually these are multistage pumps,
and are provided with guide vanes. These pumps may have
horizontal or vertical shafts. Vertical shafts are useful in deep
wells.
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59. Specified Speed
Specific speed of a pump is defined as the speed of a
geometrically similar pump which delivers unit discharge
under unit head.
Ns = N√ Q / H3/4
Types of Casing
Pumps can be divided into following type according to their
casing:
a) Volute-Chamber Pump
b) Vortex-chamber Pump
c) Diffuser Pump
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60. Work done by the impeller of
a centrifugal pump
Figure shows the velocity triangles at the inlet and outlet tips of a vane fixed to the
impeller.
Let N=speed of the impeller in RPM
D= Diameter of the impeller at inlet
D=Diameter of the impeller at outlet
U1 = Tangential velocity of the impeller at inlet πD1N/60
U2= tangential velocity of the impeller at outlet πD2N/60
V1=absolute velocity of the liquid at inlet
V2= absolute velocity of the liquid at outlet
Vf1 & Vf2 =are the velocities of flow at inlet and outlet.
Vr1 & Vr2=Relative velocities at inlet and outlet
Vw2=whirl velocity at outlet
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61. ἀ =angle made by V1 with respect to the motion of the vane
ᵩ=blade angle at inlet
ᵦ= blade angle at outlet
For a series of curved vanes the force exerted can be
determined using the impulse momentum equation
Work=force x distance.
similarly the work done/sec/unit weight of the liquid striking
the vane=1/g(Vw2u2-Vw1u1).
But for a centrifugal pumpVw2=0
Work done/sec/unit weight=Vw2u2
And the work done/sec=Q/g(Vw2u2)
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62. Pump efficiency
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6/10/2017 MAK (ME Deptt.) 62
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63. cavitation of a Pump
• Increase pressure at the suction of the pump.
• Reduce the temperature of the liquid being pumped.
• Reduce head losses in the suction piping.
• Reduce the flow rate through the pump.
• Reduce the speed of the pump impeller
6/10/2017 MAK (ME Deptt.) 63

64. • Degraded pump performance.
• Metal gets corroded seen as small pitting.
• Audiable rattling or crackling sounds which can reach a
pitch of dangerous vibrations.
• Damage to pump impeller, bearings, wear rings and seals.
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65. Reciprocating pump
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66. Reciprocating pump
• Pumps are used to increase the energy level of water by virtue
of which it can be raised to a higher level.
• Reciprocating pumps are positive displacement pump, i.e.
initially, a small quantity of liquid is taken into a chamber and
is physically displaced and forced out with pressure by a
moving mechanical elements.
• The use of reciprocating pumps is being limited these days and
being replaced by centrifugal pumps.
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67. Reciprocating pump
• For industrial purposes, they have become obsolete due to
their high initial and maintenance costs as compared to
centrifugal pumps.
• Small hand operated pumps are still in use that include well
pumps, etc.
• These are also useful where high heads are required with small
discharge, as oil drilling operations.
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68. Main components
• A reciprocation pumps consists of a plunger or a piston that
moves forward and backward inside a cylinder with the help of
a connecting rod and a crank. The crank is rotated by an
external source of power.
• The cylinder is connected to the sump by a suction pipe and to
the delivery tank by a delivery pipe.
• At the cylinder ends of these pipes, non-return valves are
provided. A non-return valve allows the liquid to pass in only
one direction.
• Through suction valve, liquid can only be admitted into the
cylinder and through the delivery valve, liquid can only be
discharged into the delivery pipe.
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69. Main components
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70. Working of Reciprocating Pump
• When the piston moves from the left to the right, a suction
pressure is produced in the cylinder. If the pump is started for
the first time or after a long period, air from the suction pipe is
sucked during the suction stroke, while the delivery valve is
closed. Liquid rises into the suction pipe by a small height due
to atmospheric pressure on the sump liquid.
• During the delivery stroke, air in the cylinder is pushed out
into the delivery pipe by the thrust of the piston, while the
suction valve is closed. When all the air from the suction pipe
has been exhausted, the liquid from the sump is able to rise
and enter the cylinder.
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71. Working of Reciprocating Pump
• During the delivery stroke it is displaced into the delivery pipe.
Thus the liquid is delivered into the delivery tank
intermittently, i.e. during the delivery stroke only.
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72. Classification of Reciprocating pumps
Following are the main types of reciprocating pumps:
• According to use of piston sides
– Single acting Reciprocating Pump:
If there is only one suction and one delivery pipe and the
liquid is filled only on one side of the piston, it is called a
single-acting reciprocating pump.
– Double acting Reciprocating Pump:
A double-acting reciprocating pump has two suction and
two delivery pipes, Liquid is receiving on both sides of the
piston in the cylinder and is delivered into the respective
delivery pipes.
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73. Classification of Reciprocating pumps
• According to number of cylinder
Reciprocating pumps having more than one cylinder are called
multi-cylinder reciprocating pumps.
– Single cylinder pump
A single-cylinder pump can be either single or double
acting
– Double cylinder pump (or two throw pump)
A double cylinder or two throw pump consist of two
cylinders connected to the same shaft.
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74. Classification of Reciprocating
pumps
• According to number of cylinder
– Triple cylinder pump (three throw pump)
A triple-cylinder pump or three throw pump has three
cylinders, the cranks of which are set at 1200 to one
another. Each cylinder is provided with its own suction
pipe delivery pipe and piston.
– There can be four-cylinder and five cylinder pumps also,
the cranks of which are arranged accordingly.
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75. Discharge through a Reciprocating
Pump
Let
A = cross sectional area of cylinder
r = crank radius
N = rpm of the crank
L = stroke length (2r)
Discharge through pump per second=
Area x stroke length x rpm/60
This will be the discharge when the pump is single acting.
60
N
LAQth 
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76. Discharge through a Reciprocating
Pump
Discharge in case of double acting pump
Discharge/Second =
Where, Ap = Area of cross-section of piston rod
However, if area of the piston rod is neglected
Discharge/Second =



 

60
)(
60
LNAAALN
Q P
th
60
)2( LNAA
Q P
th


60
2ALN
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77. Discharge through a Reciprocating
Pump
• Thus discharge of a double-acting reciprocating pump is
twice than that of a single-acting pump.
• Owing to leakage losses and time delay in closing the
valves, actual discharge Qa usually lesser than the
theoretical discharge Qth.
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78. Slip
Slip of a reciprocating pump is defined as the difference
between the theoretical and the actual discharge.
i.e. Slip = Theoretical discharge - Actual discharge
= Qth. - Qa
Slip can also be expressed in terms of %age and given by
 10011001
100%
d
th
act
th
actth
C
Q
Q
Q
QQ
slip










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79. Slip
Slip Where Cd is known as co-efficient of discharge and
is defined as the ratio of the actual discharge to the
theoretical discharge.
Cd = Qa / Qth.
Value of Cd when expressed in percentage is known as
volumetric efficiency of the pump. Its value ranges
between 95---98 %. Percentage slip is of the order of 2%
for pumps in good conditions.
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80. Negative slip
• It is not always that the actual discharge is lesser than
the theoretical discharge. In case of a reciprocating
pump with long suction pipe, short delivery pipe and
running at high speed, inertia force in the suction pipe
becomes large as compared to the pressure force on the
outside of delivery valve. This opens the delivery valve
even before the piston has completed its suction stroke.
Thus some of the water is pushed into the delivery pipe
before the delivery stroke is actually commenced. This
way the actual discharge becomes more than the
theoretical discharge.
• Thus co-efficient of discharge increases from one and
the slip becomes negative.
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81. Power Input
Consider a single acting reciprocating pump.
Let
hs = Suction head or difference in level between centre line of
cylinder and the sump.
hd = Delivery head or difference in between centre line of
cylinder and the outlet of delivery pipe.
Hst = Total static head
= hs + hd
Theoretical work done by the pump
= ρ Qth g Hst
 ds hhg
ALN







60

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82. Power Input
Power input to the pump
However, due to the leakage and frictional losses, actual power
input will be more than the theoretical power.
Let η = Efficiency of the pump.
Then actual power input to the pump
 ds hhg
ALN







60

 ds hhg
ALN







60
1


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83. Comparison of Centrifugal and Reciprocating
Pumps
Centrifugal Pumps Reciprocating Pumps
1. Steady and even flow 1. Intermittent and pulsating flow
2. For large discharge, small heads 2. For small discharge, high heads.
3. Can be used for viscous fluids e.g.
oils, muddy water.
3. Can handle pure water or less
viscous liquids only otherwise valves
give frequent trouble.
4. Low initial cost 4. High initial cost.
5. Can run at high speed. Can be
coupled directly to electric motor.
5. Low speed. Belt drive necessary.
6. Low maintenance cost. Periodic
check up sufficient.
6. High maintenance cost. Frequent
replacement of parts.
7. Compact less floors required. 7. Needs 6-7 times area than for
centrifugal pumps.
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