A 3/4 HP 10 GPM shallow well pump for irrigation ran dry for a couple hours due to a technical failure where a feeding valve mounted at the pump inlet blew out of its hole. All the water being pumped escaped from the hole and allowed the pump to lose prime and run dry. When I got to it everything was really hot.

After fixing the PVC and re-priming I tested the GPM and determined I have 50% less (5 GPM). I need the full 10 GPM for my system to work properly.

What exactly failed inside my pump from running dry and can I fix it? I have had this pump apart in the past for another reason so I am comfortable with replacing parts inside.

I'd rather buy overhaul kit parts for $30 than a new pump for $200, but if you think it's too far gone and might not work fully to 10 GPM after the repairs I'll just get the new pump.


Dry Pump failure modes

Some irrigation pumps are created the impeller housing casting an integral part of the motor and depend on the water flow through the pump to dissipate heat instead of using rotor fins and airflow for cooling. The reason for doing this is that they tend to be in high moisture locations or locations where detritus can be sucked into the pump and cause a fire hazard. With no cooling, the field windings will get really hot and can cause the thermal shutdown to trip, causing the pump to cycle on and off as it heats and cools. The heat can destroy the enamel insulation on the coils, causing them to short.

The impeller shaft seal being run dry can burn it out due to friction and lack of water lubrication. You will know when this happens as there will be a leak.

If the pump has a plastic impeller and it gets too hot, it can warp or loosen on the shaft if it's a press-on fit.

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9 times out of 10 (maybe more), the dynamic seal is the first thing to fail, as this is by far exposed to the most friction in the pump. This should be fairly obvious by the leaking water, unless it's a submersible in which case you would see exactly the behavior you're seeing.

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