Centrifugal & Reciprocating Pumps

In this report , I shall shade the light on the two types :
1- Reciprocating positive displacement pumps .
2- Centrifugal dynamic pumps.
 The comparison will include the following points for each type :
1- Working principle.
2- Usage.
3- Efficiency
4- Connection Methods (in series and in parallel )

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2. TABLE OF CONTENTS
Introduction ................................................................................... 1
1. Centrifugal Pumps…………………………………..……………3
1.1 Working Principle
1.1.1 Components of Centrifugal Pumps
1.1.2 Working Theory
1.2 Usage
1.3 Efficiency
1.4 Connection Methods
2. Reciprocating Pumps……………………………………………11
2.1 Working Principle
2.1.1 Components of Reciprocating Pumps
2.1.2 Working of a single-acting reciprocating pump
2.1.3 Working of a double-acting reciprocating pump
2.2 Usage
2.3 Efficiency
3. References ............................................................................... 16

3. 1
Introduction
 A pump is a contrivance which provides energy to a fluid in a fluid system; it assists to
increase the pressure energy or kinetic energy, or both of the fluid by converting the
mechanical energy.
 The classification of pumps according to operating principle is shown below:











 In this report , I shall shade the light on the two types :
1- Reciprocating positive displacement pumps .
2- Centrifugal dynamic pumps.

 The comparison will include the following points for each type :
1- Working principle.
2- Usage.
3- Efficiency
4- Connection Methods (in series and in parallel )




Pumps
Others
(impulse or
Buouancy ...)
Dynamic
Centifugal Special effect
Positive
Displacement
Rotary
Internal Gear External Gear Lope slide vane
Reciprocating

4. 2

5. 3
1. Centrifugal Pumps
1.1WORKING PRINCIPLE
 A centrifugal pump is a pump which raises the water from a lower level to a higher level
by the action of centrifugal force.
 For better Understanding the working principle of centrifugal pumps, it’s convenient to
cover the parts of centrifugal pump.
1.1.1 COMPONENT PARTS OF A CENTRIFUGAL PUMP
 Refer to Fig.1, A centrifugal
pump consists of the following
main components:
1. Impeller : a wheel (or rotor) with a
series of backward curved vanes (or
blades). It is mounted on a shaft which
is usually coupled to an electric motor.
2. Casing : The casing is an airtight
chamber surrounding the pump
impeller. It contains suction and
discharge arrangements, supporting for
bearings, and facilitates to house the
rotor assembly. It has provision to fix
stuffing box and house packing
materials which prevent external
leakage.
The essential purposes of the casing
are:
(i) To guide water to and from the
impeller, and
(ii) To partially convert the kinetic energy into pressure energy.
3. Suction pipe. The pipe which connects the centre/eye of the impeller to sump from which liquid is to be
lifted is known as suction pipe.
o In order to check the formation of air pockets the pipe is laid air tight.
o To prevent the entry of soid particles, debris etc. into the pump the suction pipe is provided with
a strainer at its lower end.
o The lower end of the pipe is also fitted with a non-return foot valve which does not permit the
liquid to drain out of the suction pipe when pump is not working; this also helps in priming.
4. Delivery pipe
The pipe which is connected at its lower end to the outlet of the pump and it delivers the liquid to the
required height is known as delivery pipe.
A regulating valve is provided on the delivery pipe to regulate the supply of water.

Figure 1 – Components of Centrifugal pumps

6. 4
1.1.2 WORKING OF A CENTRIFUGAL PUMP
 A centrifugal pump works on the principle that when a certain mass of fluid is rotated by
an external source, it is thrown away from the central axis of rotation and a centrifugal
head is impressed which enables it to rise to a higher level.

 The working /operation of a centrifugal pump is explained step-wise below:

1. The delivery valve is closed and the pump is primed that is, suction pipe, casing and
portion of the delivery pipe up to the delivery valve are completely filled with the
liquid (to be pumped) so that no air pocket is left.

2. Keeping the delivery valve still closed the electric motor is started to rotate the
impeller. The rotation of the impeller causes strong suction or vacuum just at the eye
of the casing.


3. The speed of the impeller is gradually increased till the impeller rotates at its normal
speed and develops normal energy required for pumping the liquid.

4. After the impeller attains the normal speed the delivery valve is opened when the
liquid is continuously sucked (from sump well) up the suction pipe, it passes through
the eye of casing and enters the impeller at its center or it enters the impeller vanes at
their inlet tips. This liquid is impelled out by the rotating vanes and it comes out at
the outlet tips of the vanes into the casing. Due to impeller action the pressure head
as well as velocity heads of the liquid are increased (some of this velocity heads is
converted into pressure head in the casing and in the diffuser blades/vanes if they are
also provided).
5. From casing, the liquid passes into pipe and is lifted to the required height (and
discharged from the outlet or upper end of the delivery pipe).
6. So long as motion is given to the impeller and there is supply of liquid to be lifted
the process of lifting the liquid to the required height remains continuous.
7. When pump is to be
stopped the delivery
valve should be first
closed, otherwise
there may be some
backflow from the
reservoir.

7. 5
1.2USAGE
i. Oil refineries and power plants.
ii. Municipal water applications.
iii. They are used to move the general water supply from the pressure main in cases
where a little or no suction lift is required.
iv. They can also be used for boiler feed applications, wastewater management, flood
protection, drainage and irrigation.
v. Centrifugal pumps also have numerous building applications. They are used to
provide booster service into homes. They are also used in fire protection sprinkler
systems or to circulate hot water. They can also be used for drainage and air
conditioning systems.
vi. The chemical and process industries use centrifugal pumps for applications such as
chemicals, paints, petrochemicals, pharmaceuticals, cellulose, hydrocarbons, food and
beverage production and sugar refining.
vii. The mining industry uses centrifugal pumps as froth pumps, separating bitumen and
minerals from clay and sand. They also use them to transport solids and slurries.
1.3EFFECIENCY
 In Order to derive the equations of efficiency, Refer to fig.2 that shows a portion of the
impeller of a centrifugal pump with the one vane and the velocity triangles at the inlet
and the outlet tips of the
vane.
o ??????
1= Raduis of the impeller at
inlet
o N = Speed of the impeller in
r.p.m.,
o ω = Angular velocity =
(
2????????????
60
) &#3627408479;??????&#3627408465;/&#3627408480;&#3627408466;&#3627408464;
o &#3627408456;
1 = Tangential velocity of the
impeller at inlet =?????? ??????
1
o ??????
2= Raduis of the impeller at
outlet
o &#3627408456;
2 = Tangential velocity of
impeller at outlet = ?????? ??????
2
o &#3627408457;
1 = Absolute velocity of water
at inlet,

8. 6
o &#3627408457;
&#3627408484;1 = Velocity of whirl at inlet,
o &#3627408457;
??????1 = Relative velocity of liquid at inlet,
o &#3627408457;
&#3627408467;1 = Velocity of flow at inlet,
o α = Angle made by absolute velocity (&#3627408457;
1) at inlet with the direction of motion of vane,
o θ = Angle made by the relative velocity (&#3627408457;
??????1) at inlet with the direction of motion of vane, and
o &#3627408457;
2 , &#3627408457;
&#3627408484;2 &#3627408457;
??????2 &#3627408457;
&#3627408467;2, β and φ are the corresponding values at outlet.
1.3.1 Efficiencies of a Centrifugal Pump
The various efficiencies of a centrifugal pump are:
(i) Manometric efficiency (η
&#3627408474;??????&#3627408475;&#3627408476;),
(ii) Volumetric efficiency (η
&#3627408483;),
(iii) Mechanical efficiency (η
&#3627408474;), and
(iv) Overall efficiency (η
&#3627408476;).

(i) Manometric efficiency (??????
&#3627408526;??????&#3627408527;&#3627408528;) The ratio of the manometric head developed by the
pump to the head imparted by the impeller to the liquid.







Where Hmano = Head imparted by the impeller to liquid – loss of head in the pump (i.e.
impeller, and casing )

9. 7
(i) Volumetric efficiency (??????
??????) The ratio of quantity of liquid discharged per second from
the pump to quantity passing per second through the impeller.
(ii) Mechanical efficiency (??????
&#3627408526;), The ratio of the power delivered by the impeller to the
liquid to the power input to the pump shaft.

(iii) Overall efficiency (??????
&#3627408528;). The ratio of power output of the pump to the power input to
the pump.



1.3.2 Effect of Outlet Vane Angle (φ) on Manometric Efficiency
The total energy of liquid before entering the impeller, with reference to the center of
pump, is taken as zero. After leaving the impeller, the liquid has a pressure energy
(Hmano) and kinetic energy
&#3627408457;
2
2
2&#3627408468;
.
The energy supplied to the impeller is
&#3627408457;
??????2 &#3627408456;
2
&#3627408468;

Neglecting the losses in the pump and equating the energy given to the impeller to the
increase in total energy, we have

10. 8








From velocity triangle at outlet



Computing the value of &#3627408456;
2 in terms of Hmano from eqn..1 for different values of φ, it will be
observed that as the value of φ varies from 90° to 20°

The value of ηmano increases from 0.47 to 0.73. A further decrease in the angle φ will increase
the efficiency, but it is impracticable to have the angle φ less than 20°, as it would result in long
and narrow blades, with very high frictional losses. As such the minimum value of φ is 20°.




.....Equ.1

11. 9
1.4CONNECTION METHOD S
 A multi-stage centrifugal pump is one which has two or more identical impellers
mounted on the same shaft or on different shafts. The important functions performed
by a multi-stage pump are:
o To produce heads greater than that permissible with a single impeller,
‘discharge remaining constant’. The task can be achieved by ‘series
arrangement’ where in the impellers are mounted on the same shaft and
enclosed in the same casing.
O To discharge a large quantity of liquid, ‘head remaining same’. This task is
accomplished by ‘parallel arrangement’ wherein impellers are mounted on
separate shafts.
Pumps in Series Pumps in Parallel


1- For obtaining a high head, a number of
impellers are mounted in series or on the
same shaft.
2- The discharge from impeller–1 passes through
a guided passage and enters the impeller–2.
At the outlet of impeller–2, the pressure of
water will be more than the pressure of water
at outlet of impeller–1.
3- if more number of impellers are mounted on
the same shaft the pressure at outlet will be
increased further. If in each stage, the
manometric head imposed on the liquid is
Hmano, then for n identical impellers the total
head developed will be; Htotal = nH, however,
the discharge passing through each impeller is
same.
4- The series arrangement is employed for
delivering a relatively small quantity of liquid
against very high heads.
1- When a large quantity of liquid is required to
be pumped against a relatively small head
(which is impossible for a single pump to
accomplish), two or more pumps are
employed which are so arranged that each of
these pumps working separately lifts the liquid
from a common sump and delivers it to a
common collecting pipe through which it is
carried to required height.
2- This arrangement is known as pumps in
parallel (since each pump delivers the liquid
against the same head). If Q is the discharge
capacity of one pump and there are n identical
pumps (arranged in parallel) then total
discharge will be, Qtotal = nQ

12. 10

13. 11
2. Reciprocating Pumps
2.1WORKING PRINCIPLE
 The reciprocating pump is a positive displacement pump as it sucks and raises the
liquid by actually displacing it with a piston/plunger that executes a reciprocating
motion in a closely fitting cylinder. The amount of liquid pumped is equal to the
volume displaced by the piston.
 The pumps designed with disk pistons create pressures upto 25 bar and the plunger
pumps built up still higher pressures. Discharge from these pumps is almost wholly
dependent on the pump speed.
2.1.1 MAIN COMPONENTS
1. Cylinder 2. Piston
3. Suction valve 4. Delivery valve
5. Suction pipe 6. Delivery pipe
7. Crank and connecting
rod mechanism operated by
a power source e.g. steam
engine, internal combustion
engine or an electric motor.







2.1.2 Working of a single-acting reciprocating pump:
As shown in Fig.3, a single acting reciprocating pump has one suction pipe and one delivery
pipe. It is usually placed above the liquid level in the sump.
When the crank rotates the piston moves backward and forward inside the cylinder.



figure 3

14. 12
The pump operates as follows:
— Let us suppose that initially the crank is at the inner dead centre (I.D.C.) and crank rotates in
the clockwise direction. As the crank rotates, the piston moves towards right and a
vacuum is created on the left side of the piston. This vacuum causes suction valve to open
and consequently the liquid is forced from the sump into the left side of the piston. When
the crank is at the outer dead centre (O.D.C) the suction stroke is completed and the left
side of the cylinder is full of liquid.
— When the crank further turns from O.D.C to I.D.C., the piston moves inward to the left and
high pressure is built up in the cylinder. The delivery valve opens and the liquid is forced into
the delivery pipe. The liquid is carried to the discharge tank through the delivery pipe. At the
end of delivery stroke the crank comes to the I.D.C and the piston is at the extreme left position.
2.1.3 Working of a double-acting reciprocating pump:
 Refer to Fig. 4. In a double-acting reci-procating pump, suction and delivery strokes
occur simultaneously. When the crank rotates from I.D.C. in the clockwise direction, a
vacuum is created on the left side of piston and the liquid is sucked in from the sump
through value 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 on to
the discharge tank. This operation continues till the crank reaches O.D.C.

 With further rotation of
the crank, the liquid is
sucked in from the sump
through the suction valve
S2 and is delivered to the
discharge tank through
the delivery valve D1.
When the crank reaches
I.D.C., the piston is in the
extreme left position.
Thus one cycle is
completed and as the
crank further rotates,
cycles are repeated.


 Because of continuous delivery strokes, a double-acting reciprocating pump gives more
uniform discharge (as compared to a single-acting pump which pumps the liquid
intermittently). To get a still more uniform feed, invariably a multi-cylinder arrangement
having two or more cylinders is employed.
figure 4

15. 13
Fig. 5 show the variations of discharge through delivery pipe (Qd) with crank angle (θ) for
single-acting and double-acting pumps respectively.

2.2USAGE
2.2.1 Plunger pump
1.Have high efficiency.
2.Capable of developing very high pressures.
3.Low and easy maintenance






2.2.2 Piston Pump (double acting)
1.transmission of fluids or gases under
pressure.
2.Power consumption is low.
3.Ensure maximum safety.



2.2.3 Diaphragm Pump (single acting)
1.flexible diaphragm is used
(rubber, thermo-plastic, metal).
2. Can be used to make artificial hearts.
3. Can handle highly viscous liquids.
4.Can handle toxic or corrosive liquids.
5. 97% efficient.

16. 14


2.3EFFECIENCY
The total efficiency of a reciprocating pump is about 10 to 20% higher than a
comparable centrifugal pump.











Agriculture.
Chemical.
Desalination.
Horizontal Drilling.
General Industries.
Mining.
Oil and Gas.
Pulp and Paper.
Sewer Cleaning.
Steel.

17. 15
References
1. A text book of fluid mechanics and Hydraulic machines ( Er. R.K. Rajbut)
2. A text book of Hydraulics (R.S. Khurmi)
3. https://www.slideshare.net/tamanashpramanick/pumps-26818585
4. https://www.slideshare.net/orgasmic/positive-displacement-pumps?qid=a98a8f76-
a456-409f-9a6d-c6559a63019d&v=&b=&from_search=3
5. http://slideplayer.com/slide/7953508/
6. https://www.slideshare.net/Mohd_Limdi/pumps-and-types-of-pumps
7. https://www.slideshare.net/sumitnp369/reciprocating-pumps
8. http://www.pumpsolutions.com.au/best-uses-for-centrifugal-pumps/