My sears compressor starts pumping fine until about 60psi and then the pump stops and the electric motor keeps running squealing the belt.when i shut it off and turn the pulley by hand the pump turns free and easy.
Mmmm, yes, that is odd.
As the pressure in the tank increases towards cut out pressure, the load (the work the pump and consequently the motor has to do to pump more air) increases.
So, it seems to me that as the load increases the harder work is stalling the pump.
It could be that the heat that is generated by the pumping process, causing something to bind in the pump, stopping the pump sheave, and forcing the belt to move through the sheave groove instead of rotating the sheave. This would create the squealing sound you hear.
You say that you remove the belt, and the pump sheave turns easily by hand, which seems to contradict what I’ve just said.
Unless, the time it takes you to disconnect the belt allows the unit to change (cool?) in some way that relieves the binding.
First thing though? Check the alignment between the two sheaves as well as the mount of the pump and motor to ensure that as the back pressure grows, that isn’t forcing them out of proper alignment?
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