Pump Net Positive Suction Head Test (NPSH Test)
The following curve illustrates that cavitation is not happening on the curve (a) because suction pressure is higher than vapor pressure.  Contrary, the curve (b) illustrates a cavitation problem because the suction pressure is less than vapor pressure. The suction section is the Achilles heel of the centrifugal pump.
The test for NPSH required is a simple one for you to do, just as long as you remember that the NPSH required increases with capacity. The more fluid you pump, the more NPSH you need to stop your product from vaporizing. Here is how the pump manufacturer did the test at his facility. To duplicate it you will need:
Centrifugal Pump Performance Test procedure
Normally job seal is used during the performance test. Seals shall be check for leakage during performance testing. If visible leakage is observed the seal must be removed, inspected and repaired as required. The repaired and installed seal must be hydro tested with water at 100 PSI or observed during a subsequent running test to have no visible leakage.
Each manufacturer may use a different setup for testing vertical pumps. Some manufacturers use a wet pit, while some may use a pump can. Different types of meters measure flow, and different methods measure head. Power can be measured as input power to the motor, or input power to the pump using torque and speed. Regardless of the pump test setup, the tested pump should include all major components of the installed pump. These components include the bowl assembly, column pipe assembly, discharge head and motor.
Centrifugal Pump Lexicon
Current methods used for testing the NPSHR of submerged centrifugal LNG pumps cannot be performed in real time while the pump is running. This is due to the fact that current methods assume ideal methane as a working fluid and assume that the test will be performed with the working fluid in a constant, thoroughly saturated state.
How pump vendors calculate net positive suction head required by the pump?
For higher capacity pumps it’s not feasible to increase temp of incoming fluid or to decrease suction tank pressure, so they use suction valve to gradually reduce the fluid flow at pump inlet. And flow is reduced until there is a decrease in discharge pressure.
What is a Pump Test?
in which PT is inlet total pressure, Pv is vapor pressure of the fluid, r is density, and g is acceleration of gravity. Net Positive Suction Head required, NPSHr, is a very important parameter for centrifugal pumps. It is also referred to as NPSH3 per API 610, 11th ed. It determines when a pump will operate at three percent loss of head due to cavitation.
Certified Pump Test Lab
Our mission is to work hand-in-hand with our valued customers to optimize the performance and reliability of their pumping systems by evaluating and understanding root causes of pump degradation or failure and by providing unbiased engineering analysis, quality workmanship, and responsive field service for improved plant operation.