Compressor Issue

[novaboy009]

I have a 10 year old Porter Cable 135 psi 7.5 horse 60 gallon compressor. Compressor kicks on from 0 psi and fills to 125 just fine (tested about 5 times). When I use the compressor and it drops below the 95 psi lower limit on the pressure switch, the motor doesn't kick back on. If I deflate the compressor, turn the compressor wheel, and hit the motor restart, it fires back up. It never trips the breaker, but it seems to trip the motor overload. It has a new pressure switch (I thought the old one just wasn't firing when it hit the low pressure zone). Motor and compressor seem to spin freely.

Thoughts?

Kev

 

[larry_g]

I would suggest that you check or replace your start cap. I also would check the the unloader for the head is releasing, do you hear it blow off when the pump stops? You could also have a check valve that is leaking pressurizing the cylinder again. To check this bring up the compressor to cutoff and after cutoff, remove t he electrical power then break the fitting on the compressor discharge pipe. If there is air releasing from the pipe then the check valve is bad.

lg
no neat sig line

 

[novaboy009]

I don't hear a whoosh after the motor cuts off at full pressure, come to think of it. What would I do to get that operational again? I'm mechanically inclined, but have very little knowledge of compressors other than how to use the tools that attach to the air hose!

Kev

 

[zkling]

Sounds like a check valve issue, which is keeping full pressure on the pump causing it to put extra resistance on the motor. Hence it will start at 0psig when there is no extra force on the pump's piston, but when fully loaded you are fighting tank pressure.

When the compressor is "full" at ~125psi. Try and listen for air leaking back through the intake on the pump. My money would be on the check valve. The motor itself is probably fine, especially if it starts up like it should when the compressor is empty.

If you can post a pic of the compressor's pneumatic workings I can point to where the check valve is. You might just be able to clean it, or may have to replace the entire assembly. Depending. They aren't very expensive usually.

 

[novaboy009]

Here is a link to the Porter Cable diagrams (compressor diagram is under "exploded art, detail #2).

http://servicenet.portercable.com/Products/Detail?productNumber=C7510

Am I looking for part # 17 - VALVE CHECK 1/2NPT?

I looked through the user manual and it said:

Problem:
Motor will not run

Causes/Solutions:
Motor overload protection switch has tripped.
Let motor cool off and overload switch will automatically reset.

Tank pressure exceeds pressure switch "cut-in" pressure.
Motor will start automatically when tank pressure drops below "cut-in" pressure of pressure switch.

Loose electrical connections.
Check wiring connection inside pressure switch and terminal box area. Have checked by a Trained Service Technician.

Check valve stuck open.
Remove and clean, or replace.

Possible defective motor or starting capacitor.
Have checked by a Trained Service Technician.

Paint spray on internal motor parts.
Do not operate the compressor in the paint spray area. See flammable vapor warning.

Pressure release valve on pressure switch has not unloaded head pressure
Bleed the line by pushing the lever on the pressure switch to
the "off" position; if the valve does not open, replace switch.

I replaced the pressure switch already, which appears to have an integrated release valve attached to it. So does that mean it's likely the check valve?

Kev

 

[zkling]

I replaced the pressure switch already, which appears to have an integrated release valve attached to it. So does that mean it's likely the check valve?

Kev

More than likely. Just test it by putting some air in the tank and cracking the air tube from the pump to the check valve. If air flows out of the tube, then you know your check valve is bad or sticking open.

I don't understand. Why did you replace the pressure switch? That shouldn't have any effect on the check valve operation.

Yes from the diagram Part #17 "check valve" would be the item in question. It prevents air transfer FROM the tank to the compressor head, but allows FROM the compressor head to the tank. Basically a one way valve.

One word of warning. If you do replace the check valve. Make sure the comp tank is completely empty and at 0psig. Otherwise that check valve could become a bullet when un screwing it.

 

[novaboy009]

I replaced the pressure switch because I had a spare NIB one sitting in my garage and wanted to see if it would work. Very scientific

Kev

 

[zkling]

I replaced the pressure switch because I had a spare NIB one sitting in my garage and wanted to see if it would work. Very scientific

Kev

In that case, I probably would have done the same thing. I just hate watching people waste money by throwing random parts at something in hopes it will fix the issue.

 

[p0lar]

One word of warning. If you do replace the check valve. Make sure the comp tank is completely empty and at 0psig. Otherwise that check valve could become a bullet when un screwing it.

Personal experience on that? I started to remove a fitting off a tank recently that was pressurized at 45 PSI.. I had no idea, thought it was empty (the drain turned out to be clogged, though open).

I turned the fitting a few times and could swear I heard an air leak, so I slowly turned it a little more - PSSSSHHHHH.

Luckily it held, but I didn't stick around to find out what was going to happen if it didn't.

 

[larry_g]

You could also have a check valve that is leaking pressurizing the cylinder again. To check this bring up the compressor to cutoff and after cutoff, remove t he electrical power then break the fitting on the compressor discharge pipe. If there is air releasing from the pipe then the check valve is bad.

lg
no neat sig line

I replaced the pressure switch already, which appears to have an integrated release valve attached to it. So does that mean it's likely the check valve?

Kev[/QUOTE]
In posts #2,4,& 6 three different ways to check the check valve were given. Have you done this yet? We can guess here till the cows come home but until you do a check and open that line between the compressor and the check valve no one will know for sure.

lg
no neat sig line