Speed variation on Ingersol rand T30 5 hp
(Clifton forge VA.)
It will start up and run for a few minutes and then it will slow down and speed back up about 4 or 5 times then trip the breaker thats with the valve on the outlet closed if I open the valve letting the air out fo the tank it runs at the normal speed.
with the valve closed it wont reach 15 pounds before it cuts off.I replaced the pressure switch thinking that was the problem but no luck.
Your compressor motor may be responding to increasing load (as the tank builds pressure) by acting as it does.
Just to be sure, dump the air from the tank, and pull and clean the tank check valve.
If that doesn't produce change, then you may have a mechanical problem increasing load, but I'm guessing that your motor itself is the problem.