reciprocating pump

2. Classification of reciprocating
pump
(1) According to the water being in contact with one side or
both sides of the piston:
(a)Single acting pump
(b)Double acting pump
(2) According to number of cylinder:
(a) Single cylinder pump
(b) Double cylinder pump
(c)Triple cylinder pump.

3. Reciprocating pump
 The reciprocating pump is a positive displacement pump
and consists of a cylinder, a piston a suction valve, a
delivery valve, a suction pipe, a delivery pipe and crank
and connecting rod mechanism operated by a power
source e.g. steam engine, I.C. Engine or an electric
motor.
 Positive Displacement Pumps, unlike a centrifugal
pumps, will produce the same flow at a given speed
(RPM) no matter the discharge pressure.
 A Positive Displacement Pump must not be operated
against a closed valve on the discharge side of the pump
because it will continue to produce flow until the
pressure in the discharge line are increased until the line
bursts or the pump is severely damaged

4. Working principle
 In reciprocating pumps the mechanical action causes the
fluid to move using one or more oscillating pistons, plungers
etc.
 During the suction stroke the piston moves left thus creating
vacuum in the Cylinder. This vacuum causes the suction
valve to open and water enters the Cylinder.
 During the delivery stroke the piston moves towards right.
This increasing pressure in the cylinder causes the suction
valve to close and delivery to open and water is forced in the
delivery pipe.

5. Air vessel
 Air vessel is a closed chamber containing compressed air
at the top and liquid at the bottom.
 Uses:
1. It provides uniform discharge from pump.
2. The chances of cavitation or separation are considerably
reduced.
3. A considerable amount of work is saved as frictional
resistance.
4. The pump can run at higher speed and provides higher
discharge.

6. Use of air vessel

7.  Discharge through a pump per second is given as
Where A= the cross sectional area of the piston in
L= the stroke of the piston in m
N= the speed of crank in rpm
3
3
for single acting pump
60
2
Q= for double acting pump
60
ALN m
Q
s
ALN m
s

2
m

8.  Work done by reciprocating pump per second is given as
for a single-acting pump
for a double-acting pump
 Power required driving the pump
for a single-acting pump
for a double-acting pump
(Where ρg = weight density of liquid in N/m3)
( )
60
s d
gALN
h h


2
( )
60
s d
gALN
h h


( )
60 1000
s d
gALN
h h kW



2
( )
60 1000
s d
gALN
h h kW




9. Slip & Co-efficient of discharge
 Slip = Volume swept/stroke – actual discharged/stroke
 The value of slip is generally positive.
 However in practice sometimes delivery valve opens
before suction stroke is completed, thus delivering a
greater volume of water than actually swept by the
piston. Hence the slip will be negative in such a case.
 Co-efficient of discharge
actual discharge/stroke
volume swept/stroke
act
d
th
Q
C
Q
 
Percentage slip= th act
th
Q Q
Q


10.  Pressure head due to acceleration (ha) in the suction and
delivery pipes is given as
 Where
2
cos for suction pipe
s
as
s
l A
h r
g a
 
  
2
cos for discharge pipe
d
ad
d
l A
h r
g a
 
  
length of suction/discharge pipe
a= cross section area of suction/discharge pipe
l 

11.  Work done by the pump per second due to acceleration
and friction in suction and delivery pipes
2 2
for single-acting
60 3 3
s d fs fd
gALN
h h h h
  
  
 
 
2 2 2
for double-acting
60 3 3
s d fs fd
gALN
h h h h
  
  
 
 

12. Indicator diagram

13. Indicator diagram with
acceleration and friction head
effect

14. Operating characteristic curve
Head 
Discharge
Input power
Efficiency



Discharge(ideal)
Speed N=constant