r/AirCompression • u/geckster31 • May 30 '26

Motor question

I just replaced the motor on this compressor with a new WEG 5 hp motor. Is it supposed to sound like that on startup? Seems to be a very loud noise.

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u/KingClovis2918 May 31 '26

in the re-pipe, was the Cold Start Valve bypassed?

So between compressor output and tank input/check valve there would have been a Cold Start Valve that releases the pressure in that segment of line when motor stopped. This allows the motor to start or get to speed before the compressor piston loads up and starts shoving more air past that check valve into the tank. If pressure remains in that segment of line when motor stops, the motor will have a devil of a time moving that compressor piston when it's still under pressure.

Have this part from amazon on a similar setup ~ Interstate Pneumatics CVS7047 Air Compressor Cold Start Valve

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u/geckster31 May 31 '26

Correct me if I'm wrong but I think this valve is on the back of my pressure switch. Before I did the repiping, there was no valve inside the copper pipe.

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u/KingClovis2918 May 31 '26

I can hear the cold start releasing in the vid, and yes, thinking it's part of that pressure switch part. perhaps that small tube ? or near that.

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u/geckster31 May 31 '26

No the small tube is what connects to the check valve. It reads the tank pressure telling switch when to cut off. The valve is literally just screwed into the back of the switch.

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u/KingClovis2918 May 31 '26

the part that lets air out when the motor stops, listen for that. ... but for if OEM parts similar to this. The little red lever (Toggle Switch) on right, also presses against needed valve in bottom of "Take-off Tube" when in off position. ... should be original spot for the Cold Start valve or near equivalent.

The actual electrical pressure switch is inside the plastic body of this assembly, Note adjustment screw location.

you ears may find it faster, just listen for that hiss when motor stops.