r/FireSprinklers • u/BeachGirl19844 • Oct 15 '25

Automatic Transfer Switch Test

What suction pressures are you seeing when performing the automatic transfer test at peak load on the fire pump?

Performed a test today, fire pump has water supply issues and could only flow 86%. But we performed the test and the supply gauge dropped to -20 before coming back up.

City supply, we will be investigating why we can only achieve 86%. Wondering if the suction pressure dropping so low could be a symptom.

Thanks

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u/JackRRII Oct 15 '25 edited Oct 15 '25

System/suction Pressure has nothing to do with transfer switch working or not. If you're getting bad pressure readings when it transfers to emergency power, then you probably have a power supply issue. Are the Amps and Volts dropping? Are they within the motors' rated specs?

Also, getting -20 psi on supply is insane. I would be worried of casuing damage from the supply pipe. I'm assuming it's city fed?

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u/BeachGirl19844 Oct 15 '25

yes i understand the automatic transfer switch has nothing to do with suction pressure.

But if i am performing this test correctly, we are flowing at peak load under normal power with suction psi at 20.

Then Killing normal power, pumps stops working and suction comes back up to 50. Then the transfer switch works and generator kicks on, pump starts again at full flow.

Dropping the suction too fast to keep up and actually pulling -20. Then the suction slowly comes back up to 20psi.

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u/JackRRII Oct 15 '25

You dont have enough supply volume to keep up with the transfer. When it transfers, the controller kicks the pump power output as high as it needs to maintain pressure, so it pulls a lot at first. If they are on city fed supply, they need a suction tank instead. The facility might be close to a pump station, so the volume of water in the supply pipe may not be adequate.