Douglas Krantz - Technical Writer - Describing How It Works

The Fire Pump was Very Hot - What Happened?

Water pumps are interesting. They use lots of energy to pump water. If the water doesn't move even though the pump is trying to push the water, all that happens is the energy going to the pump winds up heating the water.

300 Gallon fire fighting water tank that is filled by a water pump which is powered through a pressure switch
This is a fire fighting water tank, it's big. To give an idea of how big, a normal pressure tank used for home well systems is often something like 15 to 30 gallons. A hot water heater in the basement is often as large as 60 gallons. This fire fighting water tank is 300 gallons - five times larger than most hot water heaters. (300 gallons is 1135 liters).

Hi Douglas,

I was trying to find some answers online to explain what happened in our situation.

Our fire pump is connected to a 300 gallon water tank. We have well water.

Last night my husband heard noise in laundry room and asked me if I was doing anything in there. I was not, so we checked and heard a constant running of the pump. It was causing a vibration and friction with the PVC that connected it to the water tank. The PVC looked loose and came undone and then water started spurting out.

We used the water shutoff valve to stop the water and turned off the fire pump at the breaker as it was still running. About 60 gallons were released from the pipe before we were able to shut things down.

Also, the pump was very hot.

Why would something like this happen?

Thank you for your time.

Thank you, M C

I'm not there, but I can guess, at least.

Your tank has a pressure sensing switch which might not be working correctly. Either the electrical part or the actual pressure sensing part might be stuck in the "pump-on" position, keeping the pump running even though there is enough water in the tank.

The pump, if it is staying on, is going to continue to try to put water in the tank even though the tank is full.

Closing the valve on the pump won't do anything to the switch, so the pump will continue to run even if the valve is closed.

When the pump is running, electrical power is being used to turn the pump. The energy being used to turn the pump has to go somewhere. Usually, the water keeps moving past the pump so the energy is carried to the tank, ever so slightly heating up the water in the tank. If the water is stuck at the pump, however, the water will be accumulating this energy and after a while heat up so the pump will feel hot.

Basically, if the pump is running but not moving the water, the water will slowly heat up.

You need to get someone in there who normally works on home fire sprinkler systems to fix the problem because right now, your house is not protected from fire.

Douglas Krantz
Life Safety
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