Major Factors Affecting the Pump Performance

A Pump or Pumping system is the major equipment in any process or power plant. So the equipment should operate properly to give the best output in terms of performance. However, there are many factors that influence the pump’s performance. Out of those, the main (major) factors which affect the performance of the 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, β2<90°
• Forward curved blades, β2>90°
• Radial blades, β2=90°

The following table provides a guideline for pump performance with various blades.

	Backward curved blades, β2<90°	Forward curved blades, β2>90°
No of blades	12-16	60
Blade angle, β2	40°	145°
Hydraulic efficiency	80%	70%
Power consumption	low	high
application	Changing operating condition	Fixed duty operation
losses	low	high

Improper Priming

All the air in the pipeline should be expelled completely

Precautions to eliminate trouble :

• The pump should be primed completely before starting
• The suction pipe should be 1m below the lowest water level
• It should be completely airtight
• Eccentric reducers should be used if necessary to avoid air pockets in the pipeline

Insufficient NPSH

• NPSH= (P_atm-P_v)/ ρg – hs – hfs
• NPSH depends on the temperature of the operating liquid
• Variation in water level is considerable – The lowest level should be taken into account for NPSH determination
• Frictional losses should be kept minimum by selecting a suitable diameter.
• It is commonly accepted the static head in the pump will be maintained at 6.7m for water with a temperature of 10-20°c
• NPSH available > NPSH required

Reduced Capacity

• One of the main reasons for the reduced capacity is increased head
• Total head > designed head
• The 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
• The pump fails often to operate
• Remedy :
  • arrow cast is indicated in the pump casing
  • care should be taken while mounting the impeller

Clogging of Suction Pipeline

• The suction pipe is clogged by some bricks, wood often
• The strainer is clogged by paper, leaves
• To rectify this pipeline should be inspected periodically

Improper Shaft Alignment

• It is due to the misalignment of the motor and pump shaft
• It results in 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 a proper dynamic balance of the shaft and impeller
• The cavitations are reduced by properly designing the pump with suitable NPSH

Few more resources for you..

Pumps & Pumping Systems: A basic presentation
Cause and Effect of Pump Cavitation
NPSH for Pumps: Explanation and Effect
Water Hammer Basics in Pumps for beginners