Basics of Pump Assessment

The work performed by a pump is a function of the total head and of the weight of the liquid pumped in a given time period. Pump shaft power (Ps) is the actual horsepower delivered to the pump shaft. It can be calculated as follows:

Pump Shaft Power (Ps) = Hydraulic power (hp) / Pump efficiency (ηpump)

Pump Efficiency (ηpump) = Hydraulic power / Pump shaft power (Ps)

Pump output, water horsepower or hydraulic horsepower (hp) is the liquid horsepower delivered by the pump, and can be calculated as follows:

Hydraulic Power hp = Q (m3/s) x (hd - hs in m) x ρ (kg/m3) x g (m/s2) / 1000

            Where:

            Q = flow rate

            hd = discharge head

            hs = suction head

            ρ = density of the fluid

            g = acceleration due to gravity

Difficulties in Pump Assessment

• Absence of pump specification data to assess pump performance - Pump specification data are required to assess the pump performance. Most companies do not keep original equipment manufacturer (OEM) documents that provide these data. In these cases, the percentage pump loading for a pump flow or head cannot be estimated satisfactorily.
• Difficulties in flow measurement and flows are often estimated - It is difficult to measure the actual flow. The methods are used to estimate the flow. In most cases the flow rate is calculated based on type of fluid, head and pipe size etc, but the calculated figure may not be accurate. Another method is to divide the tank volume by the time it takes for the pump to fill the tank. This method can, however, only be applied if one pump is in operation and if the discharge valve of the tank is closed. The most sophisticated, accurate and least time consuming way to measure the pump flow is by measurement with an ultrasonic flow meter.
• Improper calibration of pressure gauges & measuring instruments - Proper calibration of all pressure gauges at suction and discharge lines and other power measuring instruments is important to obtain accurate measurements. But calibration has not always been carried out.  Sometimes correction factors are used when gauges and instruments are not properly calibrated. Both will lead to incorrect performance assessment of pumps.

If you have any queries regarding pump assessment, feel free to get in touch with Darling Pumps. Our ability to integrate different systems to provide customized technical solutions has made us the leader for custom pumping solutions in India. 
For further details, visit www.darlingpumps.in or call +91 99819 92838.