Pump performance assessment

Frequently asked questions

1 How would you measure the flow by using tracer method?

2 What are the various ways of measuring flow?

3 A pump motor draws 75 A current. The voltage is 415 V. Assuming a power factor of 0.9. Calculate the power drawn?

4 The suction head is 1m below the pump centerline. The discharge pressure shows 3 kg/cm2. The flow is calculated to be 100 m3/hr. Find out the pump efficiency.

5 The pump efficiency is 70%. The hydraulic power is calculated to be 22 kW. Find out the motor power required to drive the pump.

Purpose of the Performance Test

• Determination of the pump efficiency during the operating condition

• Determination of system resistance and the operating duty point of the pump and compare the same with design.

Performance Terms and Definitions

Pump Capacity, Q = Volume of liquid delivered by pump per unit time,m3/hr or m3/sec

Q is proportional to N, where N- rotational speed of the pump

Total developed head, H= The difference of discharge and suction pressure

The pump head represents the net work done on unit weights of a liquid in passing from inlet of the pump to the discharge of the pump.

There are three heads in common use in pumps namely

(i) Static head

(ii) Velocity head

(iii) Friction head.

The frictional head in a system of pipes, valves and fittings varies as a function (roughly as the square) of the capacity flow through the system.

System resistance: The sum of frictional head in resistance & total static head.

Pump Efficiency: Fluid power and useful work done by the pump divided by the power input in the pump shaft.

Field Testing for Determination of Pump Efficiency

To determine the pump efficiency, three key parameters are required: Flow, Head and Power. Of these, flow measurement is the most crucial parameter as normally online flow meters are hardly available, in a majority of pumping system.

The following methods outlined below can be adopted to measure the flow depending on the availability and site conditions.