Major Factors Affecting The Pump Performance
Major Factors Affecting The Pump Performance
Major Factors Affecting The Pump Performance
Pump or Pumping system is a major equpment in any process or power plants. So the equipment should opearate properly
to give best output in terms of performance. However, there are many factors which influence the pump performance. Out of
those, the main (major) factors which affect the performance of pump are:
Impeller design
Improper priming
Insufficient NPSH
Reduced capacity
Wrong direction of rotation
Clogging of suction pipeline and impeller
Improper shaft alignment
Packing troubles
Noisy operation
This article will explain these points in short.
IMPELLER DESIGN:
Backward curved blades, 2<90
Forward curved blades, 2>90
Radial blades , 2=90
The following table provides a guideline for pump performance with various blades.
IMPROPER PRIMING:
All the air in the pipe line should be expelled completely
The pump should be primed completely before starting
Suction pipe should be 1m below the lowest water level
It should be completely air tight
Eccentric reducers should be used if necessary to avoid air pockets in pipe line
INSUFFICIENT NPSH:
NPSH= (Patm-Pv)/ g hs hfs
NPSH depends on the temperature of the operating liquid
Variation in water level is considerable Lowest level should be taken in to account for NPSH determination
Frictional losses should be kept minimum by selecting suitable diameter.
It is commonly accepted the static head in the pump will be maintained as 6.7m for water with a temperature of 10-
20c
NPSH avaiable > NPSH required
REDUCED CAPACITY:
One of the main reason for the reduced capacity is increased head
Total head > designed head
Pump or the impeller should be changed to obtain the rated capacity
WRONG DIRECTION OF ROTATION:
This cause the rated capacity and head will not be obtained
Pump fails often to operate
Remedy :
o arrow cast is indicated in pump casing
o care should be taken while mounting the impeller
CLOGGING OF SUCTION PIPELINE AND IMPELLER:
Suction pipe is clogged by some bricks, woods often
Strainer is clogged by paper, leaves
To rectify this pipeline should be inspected periodically
IMPROPER SHAFT ALIGNMENT:
It is due to misalignment of motor and pump shaft
It results in the vibration and noisy operation
To avoid this two shafts should be aligned properly
NOISY OPERATION:
Air leakage in the pump
Shaft misalignment resulting in the vibration
Cavitations
They can be reduced by proper dynamic balance of the shaft and impeller
The cavitations is reduced by properly designing the pump with suitable NPSH
Considerable points while installing centrifugal pumps at site to reduce
vibration
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For proper functioning of the centrifugal pumps in any plant the following points need to be taken care while installing.
Checking the site before installation:
Make sure the foundation concrete is of sufficient strength.
Only place the pump set on a foundation whose concrete has set firmly.
Only place the pump set on a horizontal and level surface.
Refer to the weights given in the Pump general arrangement (GA) drawing.
All structural work required must have been prepared in accordance with the dimensions stated in the outline
drawing/general arrangement drawing.
Improper installation in potentially explosive atmospheres:
Comply with the applicable local explosion protection regulations.
Observe the information in the data sheet and on the name plates of pump and motor.
Installing the pump assembly:
Always install the pump set in horizontal position to ensure proper self-venting of the pump. Refer Fig. 1:
Mark the installation position of the coupling by dotting marks (balancing condition).
While the pumps coupling is disengaged, also check the direction of rotation.
Check the alignment of the coupling halves with a dial gauge (see Fig. 2). Admissible run-out of coupling face (axial)
maximum 0.1 mm. Admissible radial deviation, measured over the complete circumference, maximum 0.2 mm.
After having installed the pump set and connected the piping, check the coupling alignment and, if required, re-align
the pump set (with the motor). Any differences in shaft centre height between the pump and the motor are
compensated by means of shims.
Insert shims underneath the motor feet until the difference in shaft centre height has been compensated. Refer Fig.
3.
Fig. 3: Pump Set with Shim
Check that the coupling and shaft can easily be rotated by hand.
Always operate the pump set with a coupling guard. If the customer specifically requests not to include a coupling
guard in Vendors delivery, then the operator must supply one! Observe all relevant regulations for selecting a
coupling guard.
Check the distance between coupling and coupling guard. The coupling guard must not touch the coupling.
Check the available mains voltage against the data on the motor name plate.
Observe the manufacturers product literature supplied with the motor. Never check the direction of rotation by
starting up the unfilled pump set. Separate the pump from the motor to check the direction of rotation.
Never insert your hands or any other objects into the pump. Check that the inside of the pump is free from any
foreign objects.
The correct direction of rotation of motor and pump is in clock-wise direction (seen from the motor end). If the
direction of rotation is incorrect, check the connection of the motor and the switchgear, if any.