This document contains notes from a training session on pump hydraulics. It discusses key topics like hydraulic theory, types of pumps, pump components, how pumps interact with systems, parallel and series operation, cavitation, net positive suction head (NPSH), minimum flow requirements, effects of viscosity and speed changes, and unstable pump curves. Diagrams illustrate pump curves, system curves, NPSH curves, and how pumps operate at different flows depending on the system.

1. Page 1
Pump Hydraulics Training

2. Page 2
St Mkt, Irfan ul Haq
Pump training
KSB pump training at KSB Works
3rd April 2006
1. Hydraulic theory
2. “Ten ways to murder a pump”
3. Installation, commissioning, maintenance

3. Page 3
St Mkt, Irfan ul Haq
Pump training
1. Hydraulic theory
2. “Ten ways to murder a pump”
3. Installation, commissioning, maintenance
KSB pump training at KSB Works
3rd April 2006

4. Page 4
St Mkt, Irfan ul Haq
Pump types

5. Page 5
St Mkt, Irfan ul Haq
Pump hydraulics, impeller
inlet
outlet
rotation

6. Page 6
St Mkt, Irfan ul Haq
Pump hydraulics, main parts
A centrifugal pump consists of 4 main elements:
1 Impeller which rotates
The impeller has vanes which transfer
kinetic energy into the liquid pumped
2 Pump casing to convert kinetic energy
into potential energy and also contain
the liquid
3 Shaft to support the impeller
4 Generally a seal around the shaft to
contain the liquid

7. Page 7
St Mkt, Irfan ul Haq
Pump hydraulics, principles
A centrifugal pump:
Does not generate a vacuum, i.e. it cannot suck.
The impeller therefore has to be flooded in some way.
The flow and head developed are independent of the liquid
pumped, apart from effects of viscosity
Centrifugal Pumps deliver volumetric flow and head. All
curves are therefore expressed in m3/h and m (or equivalent
units)
Viscous liquids reduce the flow and head of the pump. More
later on this issue
1
2
3
4
E.g.: pump design 100 m3/h 102 m
on water sg 1.0 100.000 kg/h 10 Bar
on liquid sg 0.8 80.000 kg/h 8 Bar

8. Page 8
St Mkt, Irfan ul Haq
Pump hydraulics, head curve
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
flow
head
head

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St Mkt, Irfan ul Haq
Pump hydraulics, head + efficiency
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
flow
head
/
efficiency head
efficiency
Q
opt
Q opt is the point at which a pump has the highest efficiency, also
known as BEP (= best efficiency point)

10. Page 10
St Mkt, Irfan ul Haq
Pump hydraulics, head + efficiency
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
flow
head
/
efficiency
head
efficiency
Q
opt
Desirable operating range
Q min > 30% BEP Q max < 110% BEP

11. Page 11
St Mkt, Irfan ul Haq
Curve from book
Operating limits
Impeller diameters
Efficiencies
NPSH R
Power absorbed on water

12. Page 12
St Mkt, Irfan ul Haq
Pump hydraulics, system
Delivery head (pump system) consists of various parts
Static head on discharge side Hd
Friction loss on the discharge side
Pressure in system,
i.e. at the discharge vessel Pd
Friction loss on the suction side
Static head on suction side Hs
+
+
+
-
Hs
Hd
Pd

13. Page 13
St Mkt, Irfan ul Haq
Pump interaction with system
0
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20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
flow
head
/
efficiency
head
efficiency
system
Pump operates where pump and system curve intersect

14. Page 14
St Mkt, Irfan ul Haq
Pump hydraulics, system change
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
flow
head
/
efficiency
head
efficiency
system
system, lower friction losses
Note, with lower system curve, pump now delivers more flow

15. Page 15
St Mkt, Irfan ul Haq
Pump hydraulics, system change
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
flow
head
/
efficiency
head
efficiency
system
system, lower static
Note, with lower static curve, pump now delivers more flow

16. Page 16
St Mkt, Irfan ul Haq
Pump hydraulics, single operation
single inlet
single outlet

17. Page 17
St Mkt, Irfan ul Haq
Pump hydraulics, parallel operation
common
inlet
common
outlet
Valves etc. excluded for
clarity

18. Page 18
St Mkt, Irfan ul Haq
Pump hydraulics, pumps in parallel
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70
flow
head
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70
flow
head
+
0
10
20
30
40
50
60
0 20 40 60 80 100 120 140
flow
head
=

19. Page 19
St Mkt, Irfan ul Haq
Pump hydraulics, single + dual pump
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140 160 180 200 220 240
flow
head
/
efficiency
head 1 pump
efficiency
system
head 2 pumps
Example
1 pump
running:
total flow =
120 m3/h
2 pumps
running:
total flow =
160 m3/h
flow per pump
= 80 m3/h
Note with 1 pump running, flow is more than 1/2 of 2 pumps running

20. Page 20
St Mkt, Irfan ul Haq
Pump hydraulics, Parallel operation
Issues to be considered:
Both pumps need to have similar shaped curves
Therefore check that:
power of motor is adequate
NPSH a is adequate for the larger flow
the pump flow does not exceed the design limits
typically Q < 125% Q opt 4pole
Q< 110% Q opt 2 pole
Flow per pump will always be lower than when operating on their
own.

21. Page 21
St Mkt, Irfan ul Haq
Pump hydraulics, series operation
single inlet
single outlet

22. Page 22
St Mkt, Irfan ul Haq
Pump hydraulics, pumps in series
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70
flow
head
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70
flow
head
+
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70
flow
head
=

23. Page 23
St Mkt, Irfan ul Haq
Pump hydraulics, Cavitation
It’s this bubble collapse that causes the pump damage. This often sounds like
the pump is handling gravel. Continued cavitation will eventually destroy the
pump.
To avoid cavitation, the npsh a > npsh r of the pump
Cavitation is caused by vapour bubbles forming in the
pump.
A bubble is formed in the impeller at a point where the
‘local’ pressure is lower than the vapour pressure.
As the local pressure drops, more vapour bubbles
will form in the pump.
As the liquid flows further through the pump into a higher
pressure area the bubble collapses

24. Page 24
St Mkt, Irfan ul Haq
Cavitation on the vanes

25. Page 25
St Mkt, Irfan ul Haq
NPSH breakdown

26. Page 26
St Mkt, Irfan ul Haq
Pump hydraulics, NPSH available
NPSH available consists of various parts:
Static head on suction side
Velocity head in the pipework
This is normally ignored
Vapour pressure expressed in metres of
liquid, at the pumped temperature
+
+
-
NPSH stands for : net positive suction head
Friction losses in the suction line
-
Hs
Pe
V2/2g
Hvap
Hs
Absolute pressure expressed in metres of
liquid
Pe
NPSH available : npsh from the plant / system in which the pump operates
NPSH required : npsh that the pump needs to stop cavitation

27. Page 27
St Mkt, Irfan ul Haq
What does this mean?
So in practice this means: in the following example, we’ve ignored the
losses in the suction line
Pump with static suction head of + 5 m (Hs)
Drawing from an open tank + 10 m (Pe) atmospheric pressure is
roughly 10m with water
Handling water at 10 °C - 0.125m (Hvap) this equates to the vapour
pressure of water at 10 °C
However, contrast this with the same system at 90 Deg C:
Pump with static suction head of + 5 m (Hs)
Drawing from an open tank + 10 m (Pe) atmospheric pressure is
roughly 10m with water
Handling water at 90 °C - 7.41m (Hvap) this equates to the vapour
pressure of water at 90 °C
So NPSH available is 5 + 10 - 0.125 = 14.875 m
So NPSH available is 5 + 10 - 7.41 = 7.59 m

28. Page 28
St Mkt, Irfan ul Haq
Suction head not the same as NPSH
Therefore you can see from the previous slide that suction head is not
the same as NPSH.
The vapour pressure of the pumped liquid must be taken into account.
All pumps have an NPSH required curve. This is largely independent of
the pumped liquid, so the NPSH available and NPSH required need to
be compared to ensure that the pump will run properly.
The NPSH r curve of the pump generally indicates the value at which
the pump will cavitate. Therefore it’s important to have a margin
between the NPSH available and the NPSH required to prevent
cavitation.

29. Page 29
St Mkt, Irfan ul Haq
NPSH required
3% head drop
0% head drop
Note, when NPSH test is made, head drop is measured (3%)

30. Page 30
St Mkt, Irfan ul Haq
NPSH required

31. Page 31
St Mkt, Irfan ul Haq
Pump hydraulics, NPSH required
0
10
20
30
40
50
60
70
80
90
100
0 2 4
NPSH
head
25% Qopt
100% Qopt
125% Qopt
A number of tests will be carried out to find
the NPSH r of a pump.
These are carried out by keeping the flow
constant and gradually reducing the NPSH
until the generated head drops.
NPSH r normally classed as the point when the head drops by 3% from the
‘non cavitating’ head

32. Page 32
St Mkt, Irfan ul Haq
Pump hydraulics, minimum flow
Why min flow?
Kettle: 2kW
Capacity: 1.5 l
Time to boil: 4.5 min
Pump
Power at Q=0: 8kW
Pump volume: 2.5 l
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120
flow
head
/
power
head
power absorbed
Minimum permissible flow prevents pump from overheating
Min
flow

33. Page 33
St Mkt, Irfan ul Haq
Pump hydraulics, minimum flow
Other considerations for minimum flow:
Heat Temperature rise in the pump as losses in
the pump heat up the pumped liquid.
Pump curve Flat or unstable curve. At low flow there is
a risk of ‘hunting’
Radial loads These increase at low flow, shortening
bearing and seal life through increased shaft
deflection
NPSH req Generally increases at very low flow
Power On side channel pumps, power increases
as the flow reduces
Guideline Qmin > 15% of Q opt

34. Page 34
St Mkt, Irfan ul Haq
Pump hydraulics, speed changes
Affinity laws govern all centrifugal pumps:
Flow is proportional to Speed
Head is proportional to Speed 2
Power is proportional to Speed 3
This means for doubling the speed of a pump:
Pump speed 1450 rpm 2900 rpm
Flow 50 m3/h 100 m3/h
Head 50 m 200 m
Power 9 kW 72 kW

35. Page 35
St Mkt, Irfan ul Haq
Pump hydraulics,viscosity
0
20
40
60
80
100
120
140
0 20 40 60 80 100 120
flow
head
/
efficiency
head
viscous head
efficiency
viscous efficiency
viscosity correction factors fQ, fH, feta

36. Page 36
St Mkt, Irfan ul Haq
Pump hydraulics, casings
Diffuser + double volute
Volute
Circular Casing
Special Circular Volute
Flow Rate (Q)
BEP
Radial
Load
(F)
Double Volute
Single Volute
Diffuser

37. Page 37
St Mkt, Irfan ul Haq
Pump hydraulics, enquiry data
Capacity (Flow) m3/h l/s gpm
Pump head or diff. pressure m (bar) ft (psi)
Liquid including specific gravity
Temperature °C °F
Suction head or pressure bar psi
Materials of construction
Sealing requirements
Environment / area of use
Electrical supply V/phase/cycles
Factors for (hydraulic) pump selection:

38. Page 38
St Mkt, Irfan ul Haq
Pump hydraulics, wear ring clearances
Flow between
wear rings
Increased wear ring clearance reduces efficiency

39. Page 39
St Mkt, Irfan ul Haq
Pump hydraulics, specific speed
Radial Mixed flow Propeller
Note, units must be specified in quoting specific speed
increasing specific speed
1/2
speed x (flow )
3/4
(head)
specific speed =

40. Page 40
St Mkt, Irfan ul Haq
Pump hydraulics, suction recirculation
Suction recirculation
at low flow
1/2
speed x (flow )
3/4
(NPSH)
suction specific speed =
higher nss = lower NPSH r
but suction recirculation
more likely

41. Page 41
St Mkt, Irfan ul Haq
Pump hydraulics, Unstable curves
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70
flow
head
head
The generated head does not fall continuously as the flow increases

42. Page 42
St Mkt, Irfan ul Haq
Unstable curves, “flat” system
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70
flow
head
head
For a flat system curve, the pump could operate at one of two
flows, or hunt between the two

43. Page 43
St Mkt, Irfan ul Haq
Unstable pump curve, “steep” system
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70
flow
head
head
system
For a steep system curve, the pump can still only operate at one flow

44. Page 44
St Mkt, Irfan ul Haq
Pump hydraulics, Speed change
For a steep system curve, the pump flow will change with speed
0
10
20
30
40
50
60
0 20 40 60 80
low speed
high speed
system

45. Page 45
St Mkt, Irfan ul Haq
Pump hydraulics, Speed change, flat curve
For a flatter system curve, at low speed the pump flow may be zero.
0
10
20
30
40
50
60
0 20 40 60 80
low speed
high speed
system