I have a unique quandary that I haven't run into before. We have an overperforming fire pump.
It was factory tested, we have a factory performance curve of 68 psi churn, 52 psi at 500 gpm (100%), and 35 psi at 750 gpm (150%). Once it was field installed, we were 1-3 psi over on Churn, 50%, and 100%, but +10 psi on the 150%. We had a net pressure of 45 psi at the 150% test when, based on the factory curve, the net should have been 35 psi. We checked the nameplate for the match, nameplate for the expected pressure at 150%; they all match. The supply for the test in the field got pretty low (about 25 psi suction at 150% flow). The only unique thing I can see about this setup is that we have a very tight room and had to meet a military spec to flow through the flowmeter and both run outside as well as back to the recirculation. As a result, the path from the pump discharge to the outside has to navigate through nine (9) elbows in order to get enough clearance upstream and downstream for the flowmeter in this very tiny pump room. Could a test header with that many bends be affecting the net pressure on the 150% test? Is this considered a failure? As this is military, it'll be by the book and I'm concerned that an overperforming pump might set up future tests for failure if I can't identify why it would be overperforming at the 150%. Thanks in advance! Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
19 Comments
Dan Wilder
2/5/2024 08:02:00 am
If you're setting up the pump efficiently, flowing through the flow meter to the test header is preferred as you can calibrate the flow meter onsite without having to take equipment out of service and sending it off.
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OP
2/5/2024 08:11:23 am
Dan - great input, thank you!
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Dan Wilder
2/6/2024 07:18:20 am
Just a follow up with having no viable answer....
OP
2/6/2024 07:43:37 am
Dan - that's interesting. Flow test was 32 psi static, 30 residual at 987; so not terribly far off. That makes the pump suction 3-6 psi lower than the flow test, which is probably accounted for with the backflow preventer loss.
Bill Jones
2/5/2024 08:16:22 am
So being an electric, what are the data plate numbers and what are the actual reading numbers of amps and volts?. Are you using the controllers reading for AMP's and volts or taking them from the lugs and wires inside the controller?
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OP
2/5/2024 10:13:49 am
Sure - thanks Bill.
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Bill
2/6/2024 09:20:04 am
This is where I as a rep would turn to the sprinkler guy and say....someone owes us a change order for some more money. We gave you a better than required performing pump.
Glenn Berger
2/5/2024 08:55:34 am
I would recommend checking the water supply condition. You might have kicked on a supply pump with the higher flow rate.
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OP
2/5/2024 10:15:19 am
Right - the water supply at the suction was 39 static, then 27 psi (50%), 26 psi (100%), 23 psi (150%).
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Greg
2/5/2024 09:28:28 am
The military base may have a water supply system that is similar to some municipal arrangements, where an elevated water supply is supported by booster pumps or a refill - booster pump.
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OP
2/5/2024 10:17:38 am
Thanks Greg - I would certainly agree that it could be a culprit, however the suction pressure at 150% was still pretty consistent with the 100% test.
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Pete
2/5/2024 10:29:05 pm
I've seen a similar set up in a municipal water purveyor network, where the stage pump is designed to turn on and off based on a pressure switch. However, because the stage pump could potentially create its own feedback loop and that could lead to short cycling, a time delay was added to the start and stop after the threshold pressures are achieved. We went out to do a second flow test on a hydrant, and the water purveyor met us there. He said, "just wait". 5 minutes later we met demand pressure.
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Todd
2/6/2024 06:46:09 am
Contact the pump manufacturer and provide them with the details of your test. You have a good data set and they should be able to review along with their results and advise you of the ANSI/HI 14.6 (American National Standard for Rotodynamic Pumps for Hydraulic Performance Acceptance Tests) allowed performance variances.
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OP
2/6/2024 07:47:50 am
Thanks Todd - this is good advice. We'll send it back up the fire pump rep chain for their take.
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Todd
2/6/2024 01:45:32 pm
Not quite what I'm saying. The fact that you can get the pump out to the 150% mark (and perhaps beyond ???) indicates that you don't have a system curve that resembles a partially closed valve. The pump is a machine only capable of producing outputs related to inputs. If the friction loss through the discharge piping after the pump is too high it will artificially throttle the pump back to a specific flow rate on the pumps performance curve just like closing a valve.
Todd
2/12/2024 07:09:59 am
Once you have an identified culprit; it would be great if you could let us all know what it was... Thanks.
Greg
2/6/2024 08:56:23 am
Reading through your question again, two final thoughts;
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Jack G
2/6/2024 10:16:08 am
The pump you ordered was on an assembly line. Commonly, the factory is short parts, most typically frames, sometimes engines. They test the pump and the curve is “ off”.
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Dave Foley
2/7/2024 01:04:46 pm
Has anyone considered that If the flow meter is dumping the pressurized water back to the supply, that this will increase the suction pressure but make it look as though the pump is adding more pressure than its rating. the amount of added pressure recorded would depend on the location of the gages you're using to record the suction and discharge as well as the amount of pressure that bleads back into the city supply pipe.
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