Air Compressor Problem

[groundcoat]

Hi all. Could use your help with diagnosing a new problem with my air compressor.

I have a run-of-the-mill 1980s-ish Devillbis/ Craftsman air compressor with a 12 gallon (I think) tank and a 110v motor. About 2-3 years ago, I rebuilt most everything on it and it has been a good little workhorse for me and my needs. No problems until about a month or so ago.

When I turn the compressor on, everything works just fine until it builds about 80psi of air, and then the pump and motor really struggle building air until it eventually builds to about 110psi of air and then everything instantly goes back to normal and the compressor builds air effortlessly until the shutoff point at 125psi. Very strange.

Neither the pump or the motor are running hot. The motor has new bearings and new run/start capacitors. Both the pump and the motor run smoothly other than this 80-110psi range. I recently replaced the check valve in the tank and cleaned the reed plates in the pump head but that made no difference. The pressure switch is a Square D brand that has a 90-125psi operating range.

This just started about a month ago. What am I not seeing here? Thank you for your input. Rob

 

[sberry]

Check the belt.

 

[Kaizen]

Ditto


Sent from my iPhone using Garage Journal

 

[Citation]

Belt first then the capacitors in the motor.

 

[Ben Buck]

You using an extension cord ?

Maybe voltage drop- don't know- just asking.

Trying to give some ideas

 

[The Cobbler]

that's a weird one. I have no suggestions

 

[groundcoat]

I'm not using an extension cord. The power cord and the circuit wiring is all good 12 gauge copper. The belt looks brand new. The motor runs smooth as silk other than that 80-110psi range. The pump also turns freely. The compressor holds air forever so no leaks there. Don't know where to look next. The unloader valve? But it seems to be working. Anything else inside the pressure switch I should check? Thanks all for your input. Rob

 

[vavet]

Does the sound change during the time it's between 80 and 110 PSI? You say it's struggling - do you just mean it takes a long time to span that 30 PSI range?

You could get a kill-a-watt device to watch how much current it's drawing before it starts struggling and during the diffcult time.

 

[Citation]

At some point I would just start going down the line. The fact that the motor works well above and below that pressure and when starting suggests this isn't a motor issue. It sounds like the pump has been cleaned up. What about the check valve? Can you put the old one back in just in case as a test? You also might pull the head again. I replaced a valve in a DeWalt 55153 only to have it go bad right away I might have pinched it during install. Perhaps the valve is sitting badly and the forces acting on it in that 80-110 psi range are keeping it from seating properly. A bit more pressure seats it better or less is easier for the pump to over power.

 

[groundcoat]

During that 80-110psi range, everything slows way down and I'm sure the motor must be asking for more juice. The circuit is 20amp and not tripping. The motor or the capacitors, however, don't feel hot or even warm after the struggle so I guess that's good(?). I bought new reed plates but haven't installed them yet. I'll go back into the pump head and see if I missed anything. Thanks all, for your input. Rob

 

[Don1357]

Just for shiggles try it in an outlet wired to a different breaker/wiring.

I have a 12 gallon compressor that HATES poor electrical outlets, specially if it is outside and cold. We are not even talking extension cord here. When connected to the one on the outside of the house it would struggle to start. I would have to go inside, turn everything on that circuit off, and still try a bunch of times until it would eventually kick in. Now that my garage is properly wired the thing has 0 issues running from cold on any of the new outlets.

 

[DeeKay]

Just for shiggles try it in an outlet wired to a different breaker/wiring.

I have a 12 gallon compressor that HATES poor electrical outlets, specially if it is outside and cold. We are not even talking extension cord here. When connected to the one on the outside of the house it would struggle to start. I would have to go inside, turn everything on that circuit off, and still try a bunch of times until it would eventually kick in. Now that my garage is properly wired the thing has 0 issues running from cold on any of the new outlets.

Sounds like you have some not so great wiring in that house, or some long runs and undersized wire. If I lived there I'd be tearing that stuff out haha

 

[metlmunchr]

Does it use a poly-v belt? A lot of those sears/devilbiss compressors from that era used those belts. Curious because its much more difficult to tell if one of those belts is slipping as compared to a standard V-belt.

My guess, as several others have said, is a slipping belt. As it slips, the motor pulley will heat up pretty fast. The hot pulley will have a bit more torque capacity due to the fact that rubber tends to be more "sticky" against a hot surface.

I'd spray it with some belt dressing as a first shot. If that seems to work, then the belt should be removed and it and the pulleys cleaned, and the belt reinstalled and properly tightened. Belt dressing alone is most always just a temporary fix.

If the drive is a standard v-belt then I'd look at the profile of the motor pulley for wear. Once a pulley has significant wear in the groove it should be replaced as it will never transmit power as it should.

 

[Don1357]

Sounds like you have some not so great wiring in that house, or some long runs and undersized wire. If I lived there I'd be tearing that stuff out haha

Why? The only place that matters, garage/workshop, has a 100 amp drop directly from the panel outside. I'm good

 

[groundcoat]

Well, after looking at every minute detail of my compressor under a magnifying glass, I replaced the GFI outlet that my compressor was plugged into with a regular 20 amp receptacle and voila! It works like brand new. No more issues in that 8-110psi range. My problems with the compressor started when I installed the new circuit. I just didn't put 2 and 2 together. I wrongly focused on the compressor and dismissed that anything could be wrong with the circuit because it was all new. Still don't know why the GFI would cause issues with the compressor once it made 80psi of air.

 

[stickshift]

Well, after looking at every minute detail of my compressor under a magnifying glass, I replaced the GFI outlet that my compressor was plugged into with a regular 20 amp receptacle and voila! It works like brand new. No more issues in that 8-110psi range. My problems with the compressor started when I installed the new circuit. I just didn't put 2 and 2 together. I wrongly focused on the compressor and dismissed that anything could be wrong with the circuit because it was all new. Still don't know why the GFI would cause issues with the compressor once it made 80psi of air.

That is certainly strange. If it detected a current imbalance, the GFCI should have tripped. Almost like it throttled the current? Would be interesting to see what the voltage was at the line connection to the pressure switch in the range where the compressor bogs down.


You mentioned the circuit is new. Is the GFCI outlet also new?

Maybe post this in the electrical subforum, some of those guys might have an idea.

Glad I'm running mine off a regular 20A outlet, and after reading this, I have zero interest in switching to GFCI outlet, code be damned.

 

[redmondjp]

That is certainly strange. If it detected a current imbalance, the GFCI should have tripped. Almost like it throttled the current? Would be interesting to see what the voltage was at the line connection to the pressure switch in the range where the compressor bogs down.


You mentioned the circuit is new. Is the GFCI outlet also new?

Maybe post this in the electrical subforum, some of those guys might have an idea.

Glad I'm running mine off a regular 20A outlet, and after reading this, I have zero interest in switching to GFCI outlet, code be damned.

I don't think you have the proper understanding of what a GFCI unit does - all it does is compare the AC current on the black wire to the AC current on the white wire - if they differ by more than 5mA then it trips. It is a leakage detector and is one of the best electrical safety devices ever invented. It has nothing to do with the situation described in this post and most certainly does not "throttle" current.

 

[stickshift]

I don't think you have the proper understanding of what a GFCI unit does - all it does is compare the AC current on the black wire to the AC current on the white wire - if they differ by more than 5mA then it trips. It is a leakage detector and is one of the best electrical safety devices ever invented. It has nothing to do with the situation described in this post and most certainly does not "throttle" current.

I understand what a GFCI outlet or breaker does. Which is why I'm very surprised by the symptoms described in this thread, and why I asked if this was a new outlet.