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Centrifugal Pump Performance Test Procedures and Techniques

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In this article, we will read about the Centrifugal Pump Performance Test procedures and techniques.

The below figure shows a basic test circuit of a centrifugal pump. The Centrifugal Pump Performance Test procedures and techniques are carried out as follows, but it may slightly change based on pump manufacturer testbed condition and internal procedures.

To read about the centrifugal pump performance curve, click here

The following tests are normally carried out for centrifugal pumps

  1. Pump performance test
  2. Mechanical Run test
  3. NPSHr test

In that NPSHr test is usually carried out whenever the NPSH margin is less than 1 meter.

Centrifugal Pump Performance Test

Step 1. The Flow Vs Head(q/H) test

The number of testing points required for performance test is based on the pump code ie., API 610, ASME, NFPA 20, Hydraulic Institute (HI 1.6).

Six-point measurement is the minimum requirement for API Pumps and Five-point measurement for Non-API Pumps.

These points will range from a sub-minimum flow (Shut off) to a minimum of 120% of BEP flow sub-minimum

As per Hydraulic Institute HI 1.6, centrifugal pumps are classified as Type A & Type B.

Pump Type A:

TYPE A pumps are manufactured for special cases. For these pumps, the “Seven” measuring points are required.

Pump Type B:

TYPE B pumps are manufactured by mass production. For these pumps, the “Five” measuring points are required.

Note: All ASME pumps testing shall be as per HI 1.6.

During the performance test, the following values shall be recorded at each test point: suction pressure, discharge pressure, flow, RPM and power.

Refer below performance curve

 

Based on the flow rate (test points), the corresponding head is measured and plotted in the Flow Vs Head curve.

Other Points check during the Performance test

Speed

To ensure the test accuracy of a Centrifugal pump is pump speed.  As per API, the pump speed during the performance test shall be within the range of the + 3% of rated speed. In case the pumps at 50 Hz (ie., Operating condition) but the test facility is 60 Hz. The pump manufacture as to have the necessary arrangement for reducing the frequency from 60Hz to 50Hz and achieve the operating speed.

If the manufactures do not have the facility for step down the frequency, then they will use a gearbox to achieve the pump rated speed.

If the above facilities are not available with the manufacturer, they will be carried out the performance test at a particular speed and interpolated to rated speed.

Mechanical Seal Leak Check

Normally job seal is used during the performance test. Seals shall be checked 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.

Step 2. The efficiency test

The efficiency guarantee is checked using the same set of test measurements as the Flow Vs Head test. Pump efficiency is shown plotted against the flow as in the below figure. In most cases, the efficiency guarantee will be specified at the pump rated flow rate (q).

Step 3. Vibration measurements

At each performance test point (except shutoff point) pump bearing housing vibrations will be measured and recorded.

For between bearings pumps, vibration readings shall be measured on each bearing housing in the vertical and horizontal directions and on the thrust bearing housing for the axial direction.

For overhung pumps, vibration readings shall be taken in the vertical, horizontal and axial directions. The vibration values are within the limit mentioned in the respective pump codes.

Refer below sample test reports

Mechanical run Test

The pumps will be run at the rated flow until bearing temperatures have stabilized. Stabilization will be achieved when the bearing temperatures have changed at or less than 2 deg F in 20 min. After stabilization has been achieved, a four-hour mechanical run will be performed at the specified rated flow condition.

The bearing temperature test

Usually, this test is carried out before all performance test.

For pumps with flood oil or ring oil lubrication, sump oil temperatures are monitored during the performance test. The temperature rise values apply to the duration of the standard performance test, typically one hour or less of operation.

For pumps with oil mist, outer bearing ring temperature shall be taken. If there are no provisions for bearing temperature detectors, bearing housing skin temperature is measured.

For pumps with forced oil lubrication, temperature measurement is taken in the outlet connections on the bearing housings.

 

Temperature shall be measured before the start of the performance/mechanic run test. The recorded temperatures shall not exceed the temperature limit mentioned in the respective codes.

Maximum allowable temperature rise above ambient temperature is as follows: (The values may change slightly with different pump manufactures)

Pumps with flood oil or oil ring – 70 degrees F (21C) oil temperature.

Pumps with oil mist – 70 degrees F (21C) bearing metal or bearing housing skin temperature.

For pressurized systems, the bearing oil temperature rise shall not exceed 50 degrees F (10C).

The NPSH test

These are two common methods that are used to doing the NPSH test.

Vacuum suppression testing

The pump is supplied from a closed tank with a constant liquid level. Suction conditions are varied by the use of shop air to increase pressure above atmospheric and a vacuum pump to reduce the pressure below atmospheric.

Suction valve throttling

This method is only utilized if the pump capacity exceeds that of a closed test loop and the pump is tested on a sump. The pump is supplied from an open sump with a constant liquid level. A booster pump may or may not be utilized to simulate suction pressure above atmospheric pressure depending on the characteristics of the pump. Suction pressure is reduced by throttling a valve on the suction piping of the pump in conjunction with shutting off the booster pump.

In the above two methods, vacuum method results are the more accurate and scientific result. unobscured by the presence of the valve.

During NPSH testing, a flow is set and held constant while the suction pressure is reduced incrementally. The total developed head is monitored to determine the suction pressure point where a 3% drop in the total developed head is observed. The temperature of the test water is taken at this point to determine vapour pressure. NPSH is calculated in accordance via the latest revision of the Hydraulic Institute test standard.

Speed Corrections

Correction factors (applied to flow, Head, Power, and NPSH) need to be used if the test speed of the pump does do not match the rated speed. They are:

n = speed during the test

nsp = rated speed

Acceptance Criteria

After centrifugal pump performance test, the results are checked with the rated conditions or guaranteed point. The acceptable tolerance range is based on applicable pump manufacturing points

For API 610:

The acceptable tolerance is

For Hydraulic Institute standard

Acceptance level Type A pumps Type B pumps
Under 60 m (200 ft)

to 680 m3/h (2999 gpm)

 + 8%, – 0 +5%, -3%
Under 60 m (200 ft)

681 m3/h (3000 gpm)

and over

 + 5%, -0 + 5%, -3%
From 60 m (200 ft) to

150 m (500 ft),

any flow rate

 + 5%, -0

 

 + 5%, -3%
150 m (500 ft) and over, any flow rate + 3%, – 0

 

 + 5%, -3%
Minimum efficiency at rated

rpm and rate of flow

 np or nOA 100 / ((120/np)-0.2)

 

For pump type A: np – Contractor pump efficiency

For pump type B: np – Published, nominal efficiency

Conclusion

As mentioned at the beginning of this article, Centrifugal Pump Performance Test procedures and techniques may vary slightly to pump manufacture internal test procedures. Almost all pump manufacture will meet the acceptance criteria mentioned in this article.

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