Tolerance in Pump Curve Nameplate vs. Test?

12/17/2025

We find that the pressure and flow vary between the nameplate and the shop test curve of the UL-listed fire pump.

What is the allowable tolerance for the difference?

Thanks in advance.

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8 Comments

Dan Wilder

12/17/2025 07:43:03 am

Is this an acceptance test or an ITM procedure?

New (2019 NFPA 20)
14.2.4 - Flow variance is only allowed based on the accuracy of the test equipment which is +/-1% per 14.2.6.1.1 (so it needs to hit the points on the curve)
14.2.6.6.6 - Voltage is +10% to -5% for the driver

Experience has shown that new pumps typically run a little above the curve, especially engine drivers.

ITM (2023 NFPA 25)
8.3.2.1.2.1 - +/-5% for pressure recording
8.3.7.2.3 - 100% of rated flow, 95% of one of the following: the original pump curve, the unadjusted pump curve, test curve created from the name plate

There are other segments for variance aspects like +/-3% for flow meters but in a nutshell, Flow needs to be met, PSI is +/-5%

Pantha

12/17/2025 08:35:59 pm

The pump is installed and we identified during as built review phase. The pressure between nameplate and certified shop test curve is different. Nameplate pressure for diesel engine driven fire pump is 145 Psi but 155 Psi in the curve. Electrical Pump: 145 Psi in the 154 Psi in the curve. The difference is only for overloaded flow (150 %) but in other cases those are similar.

Rocket

12/17/2025 10:10:49 am

Is this a new pump, or an existing pump in operation?
What are your measurements in comparison with the factory curve?
For an existing pump, it is allowed maximum 5% under its shop curve pressure in all curve points before the test result is unacceptable.
And this only if the system demand is met 100% with that drop in pressure.
This is why we usually specify a pump with some safety margin, to compensate for impeller wear over time.

Pantha

12/17/2025 08:39:27 pm

The pump is installed and in operation we identified during as built review phase. The pressure between nameplate and certified shop test curve is different. Nameplate pressure for diesel engine driven fire pump is 145 Psi but 155 Psi in the curve. Electrical Pump: 145 Psi in the 154 Psi in the curve. The difference is only for overloaded flow (150 %) but in other cases those are similar.

Rocket

12/17/2025 11:08:32 pm

The nameplate displays the nominal performance characteristics.
If the pumps perform slightly better than the factory test, I see no problem.
Are you sure you are testing the pumps under the same conditions as the factory test?
Are the RPM the same? Is the static pressure the same, or are you testing with a different static pressure on the supply side?

Jack G

12/17/2025 11:55:05 am

A New fire pump is required to perform per NFPA 20, and the testing gauges and flow measuring devices are supposed to be calibrated to within 1%. It must hit the points.
Nfpa 25 --- 8.3.7.3 & 8.3.7.4 outline what is considered to be acceptable.
It states that if a pump yields results less than 95% of the pumps rated flow and pressure, than an investigation must be conducted as to why the pump is yielding a degraded performance

Qamar Shoukat

12/20/2025 02:50:31 am

If i want to download the old existing fire pump UL certificate, what is fast and easy way, i only have pump nameplate, nothing other documents I have.

Rocket

12/20/2025 11:13:48 am

FM/UL have online registries with all fire pumps they have listed.
I am not sure what you are trying to do though....

A specific listing is for the pump model, not the actual pump you are looking at.

It is just a web page with some pump characteristics.

Each pump can be configured differently.

For example a 1500 GPM pump listed by FM I am looking at right now, can supply nominal 1500 GPM at 40-66 psi depending on impeller size and HP.

Are you looking for the pump curve maybe?

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Tolerance in Pump Curve Nameplate vs. Test?

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