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Discussion Starter #1
I have a Westward 4YD76-4 135 PSI 4 gal pancake air (looks exactly like the Porter Cable as seen in this YouTube video -
) compressor that started having a problem last summer. It would start up and it would run until the 135 PSI and shutoff. I would use some air and when it got down to approx 100 PSI it would attempt to turn on but would only get a clunk noise like it wanted to start but couldn't and would continue to do that if I left the power switch on so I would turn it off until I needed more air.

So now this year I wanted to check into the problem and it will run up to 50 PSI on initial startup and turn off. Then I get the clunk noise because it is trying to start up since the pressure is below the cut-in pressure. I replaced the pressure switch, check valve & safety valve but no change. What I did notice is that I can power it off and on and it will run in short bursts of 5psi at a time before it stops again and I get the clunk noise like it wants to start. If I do this several times, it will eventually reach the 135 cut-out. I used some air and it when it hit cut-in, it would do the run for 5psi and stop, keep clunking unless I power it off. I looked at the head, the gaskets & reeds looked good. I couldn't check the piston/ring/cylinder because the cylinder is riveted to the mounting plate, but it felt snug while moving the piston. It doesn't seem like that would be the problem anyway because that would be more of a compression issue than running issue.

Any ideas/suggestions? Thanks
 

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LowTechz,

I would see if the check valve is leaking. there should be no air pressure in line between Head and tank once full pressure is achieved. Usually if the check valve leaks the head unloader valve releases a steady stream of air after top pressure is reached.The head unloader valve should be in the open position after top pressure is achieved, I would check that too to see if it is unloading air. A start capacitor or centrifugal switch could be a problem but you would hear a humming and motor would overheat and possibly trip breaker.

Stephen
 

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Reading more into your diagnosis sounds like a mechanical problem. I would check the various bearings and make sure the motor and rod bearings turn smoothly
 

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Discussion Starter #4
After more investigation, it appears to be a back pressure issue. I ran the unit for a minute & a half before I manually turned it off. If I were to run it normally, the longest it would run would be on an empty tank and that would be for about 25 seconds before it would stop. But the likely cause of back pressure issues have already been replaced, check valve, pressure relief valve & pressure switch.
 
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