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What is the best procedure to use when testing a 3,500 gallon diesel fire pump that is equipped with a throttling/pressure governor installed on it?
My graph was well below the rated curve at 50% and 100%, but the governor seemed to disengage at 150% flow and my numbers exceeded the rated curve when we pushed this much water. I did not attempt to change the controller settings or unplug the device (if that's even possible) to disengage the forced idle at 50% or 100% but insurance isn't "buying" that the pump didn't fail. These pumps aren't more than 5 years old and are ran on a tight schedule once a week (by the way). Maintenance thinks it'll lead to faster wear and tear on the motor and I agree. All I could really do was state the facts and hope I don't have to go back out there and do the test again. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
10 Comments
schulman
9/23/2022 08:32:37 am
you are allowed some "droop" 10% ..speed loss from churn to 150% per NFPA 11.2.4.1.1 (2016)
Bobby Suarez
9/23/2022 09:23:19 am
If I understand your question correctly you are referring to a Variable Speed Fire Pump. Both NFPA 20 and 25 outline the performance requirements and testing procedures for Variable Speed Pumps. Amongst the other difference between these and standard fire pumps; variable speed pumps use a 5 point performance test instead of the typical 3 point test.
Jesse
9/23/2022 10:06:18 am
I have no doubt the insurer's Loss Control engineer as well as their VP of engineering rates it having failed.
Casey Milhorn
9/23/2022 11:06:57 am
I wasn't aware you could use a VFD controller on a diesel fire pump. That's a new one on me if that's the case but we don't see a lot of VFDs anyway. If the pump didn't hit within 10% of its rating at 100%, then it should be failed. Definitely don't adjust anything yourself without direct instructions from owner or owners rep to do so. If you aren't familiar with the device, I would advise calling in the commissioning pump rep to come in that did it originally. Charge the customer for their time on site. It's possible that it is being throttled to prevent over pressurization of certain equipment and they are "flattening" the curve. If so, and hydraulic calcs are based on that, then I would advise a permanent sign be installed that says "Pump designed to provide combined X psi at 50% and combined X psi at 100%".
Franck
9/23/2022 12:20:53 pm
Working for an insurance company, I can tell you we don’t like variable speed pumps because of reliability. If the system fails, the pump willl not work properly.
John
9/23/2022 05:15:11 pm
Thanks for all the input. I spoke with 2 different manufacturer representatives and they both said the test needs to be done at constant speed, but one did say the I could try and present the Affinity Law and show them that churn was at 94% on one and 96% on the other. I sent them the calculations and I think the "smoke and mirrors" worked. I did see that NFPA 25 (2020) has the new items for the multiple test points and even says to do it at variable and constant speed unless the controller and pump manufacturer states different.
Thomas Duross
9/24/2022 04:52:37 am
You can either adjust flow and pressure by using affinity laws or disable the PLD and run full speed. You might have to close the system supply and the relief too.
Mark
9/25/2022 08:28:06 pm
Did Insurance Company or you have access to the original acceptance tests and three prior annual tests to compare?
Bill
3/13/2023 05:40:12 pm
The PLD adjusts for pressure so you'll never know the pump is not running right unless you do a 3 point test with the PLD disconnected. Of course this will always run pressures >175 psi so the discharge valve to UG & risers needs to be shut and the PRV needs to be adjusted closed to get accurate test results on the pump performance itself. Leave a Reply. |
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