Air compressor dying, need help diagnosing *VIDEO*

[spills]

I may have posted up something about this a while back, but I finally got a semi-decent video to show what I'm talking about. Basically, it's a 60 gal compressor I bought from Northern Tool about 2 years ago. Here's a link to some specs, the compressor has now been discontinued: Amazon.com: - Industrial Air Cast Iron Pump Compressor - 3.6 HP, 60 Gallon, Model# ILA7006056: Home Improvement

When the compressor kicks on, it starts pumping, then slows down pretty drastically. Over the course of 3-5 minutes, it will slowly build up speed. I thought maybe the pump was starting to seize, so I tore it down and couldn't find anything wrong (cylinder bores still had crosshatches). I thought it was the pressure switch, so I replaced it with a new unloader valve, still the same thing. I checked the check valve on the top of the tank, seems to move freely.I cannot figure out what the problem is! Tank is only at about 55psi when I flip the switch on

BTW: Someone had mentioned to me that it could be the motor, but when this first started, I heard the belt slipping on the pulley. IT doesn't do this in the video, but if that's the case I don't see how it could be the motor.

Here's the link to the video. it's in .3g2 format, I'm working on finding a converter if others cannot view this file type.

EDIT: Found a cheap converter, got it in AVI format as well

3G2 File (2.5 MB)

AVI File (15.3 MB)

[woodjames]

That was pretty neat, a lot better than just a picture. Two things - check the bolt on the fly wheel for tightness. Also, open your pressure relief, or drain valve and describe what happens when it runs without building pressure, just to get this out of the way, no insulting intended, but the belt(s) is tensioned properly right?
-Jimmy

[spills]

yea, the belt is tensioned to the right "specs", I don't think it's a belt problem though. When I tore down the pump a month ago, the tank had 0 psi. Once it fired off, it ran perfectly just like it was brand new. But once it started building pressure, say at around 50psi or so, it started to slow down. I'm not going back out to the shop until the weekend, but when I do I'll try just for S&G cracking open the relief valve and turn the pump on to see what happens. I'm going to guess that it will run fine like that, it seems that way at least.

[woodjames]

That being the case you might want to check the connections at your run capacitor. It's usually a silver color. Also, track the wire back to where it connects on the back of the motor and check it there to. Touch both the terminals on that capacitor and it will happily kill you. Unload/discharge it first by running a screwdriver with an insulated handle across the two terminals on the capacitor. After the big flash/spark you'll be okay. If it doesn't spark that will be an indicator that something is amiss. You will need to turn off the breaker too. There is a way to test the capacitors, but the place where I've gotten replacements from has always done it for me. I believe you can check for resistance, but you'll have to look up testing them to be sure. Let me know.

One other thing - Are you using/ been using an appropriately sized line and length supplying power to the compressor?

-Jimmy

yea, the belt is tensioned to the right "specs", I don't think it's a belt problem though. When I tore down the pump a month ago, the tank had 0 psi. Once it fired off, it ran perfectly just like it was brand new. But once it started building pressure, say at around 50psi or so, it started to slow down. I'm not going back out to the shop until the weekend, but when I do I'll try just for S&G cracking open the relief valve and turn the pump on to see what happens. I'm going to guess that it will run fine like that, it seems that way at least.

[spills]

that's another weird thing, about the wiring. When I first wired it up (220v), all it had was 2 hots and copper ground, no neutral. Basically, IIRC, I used a dryer cord, which I figure should be sufficient

[woodjames]

Yeah, you are probably okay with that. 2 hots and 1 ground is fine, it's actually using one of the hot legs to return the current. Basically the neutral, like when you see 3 wire is to supply 110 at the same time, like the clock on a 220v stove, or timer on a dryer...etc. Check out the run capacitor. It'll be housed under one of the covers on the motor housing. There'll be a black one as a start - which supplies extra juice up to around 75% of run speed, and then the run capacitor (silver) takes over. The motor will work w/o the capacitor, but only with no load. I've had a spade terminal look like it was connected just fine, only to turn out it had lost connection. Pull the spade connection off, slightly crimp it down with pliers, and then put it back in place.

Has the thermal overload ever tripped on it?
Just re-read my earlier post and wanted to clarify the "track to the back of the motor statement". The capacitors have two wires coming out of them. One of those two go "into" the motor. The other goes to the plate at the back of the motor. Double check the connections, and adjust as I just described at the back of the motor and on the capacitor itself.

that's another weird thing, about the wiring. When I first wired it up (220v), all it had was 2 hots and copper ground, no neutral. Basically, IIRC, I used a dryer cord, which I figure should be sufficient

[spills]

I will, though I am still doubtful it's an electrical problem. When this first started, the belt was spinning on the pulley. If it were a motor problem, I would think that it wouldn't even have enough power to do that. I'll give it a look-see though

[woodjames]

Kind of hard from my chair here, but start with those, there really wouldn't be anything else that I can think of. There's a chance it may be a reed valve in the pump itself, but I can't think of anything else pump wise. If you've gone through everything else, keep in mind, you can find single stage pumps pretty cheap - depends just how much time you want/have to put into everything.
Reed valves seemed okay when you were in the pump? Let me know how things go this weekend.

-Jimmy

I will, though I am still doubtful it's an electrical problem. When this first started, the belt was spinning on the pulley. If it were a motor problem, I would think that it wouldn't even have enough power to do that. I'll give it a look-see though

[spills]

ya, I barely pushed them open from the backside (going in the same direction as the airflow of course) and they seemed to be in good condition.

What really gets me is the fact that it starts out pumping fine, then drops in RPMs, then slowly builds up speed. It's like it's trying to overcome some pressure somewhere. I dunno, I really don't know who to call to come look at this. It's weird, everything else about my shop and house I have people I can call, but no one knows anything about air compressors, and there's really not a company that I can think of that would even come out and look at it, for cheap at least

[woodjames]

Right, back to the reed, it still has to seal well - beyond just moving. That'd be the place to start. That's sounding more like the cause the more I think about it. Definitely explains the difficulty overcoming the the 40lbs. +. Think of how much harder it would have to work, as the cylinder(s) would be trying to overcome compressed air, rather than just ambient air pressure, that and a breather that was clogged up would act in the same manner. Way back in the day, when I suggested the check valve at the tank, I forgot the pressure it takes to close those is pretty high, it'd be open still at 40lbs, so that rules out that one, and the unloader would either leak, or not release the pressure correctly at shut off, nothing to do with 40 lbs. But, if the output valve doesn't seal, and the intake does, it would definitely explain it.

Usually the reed valve kits are readily available.

-jimmy.

ya, I barely pushed them open from the backside (going in the same direction as the airflow of course) and they seemed to be in good condition.

What really gets me is the fact that it starts out pumping fine, then drops in RPMs, then slowly builds up speed. It's like it's trying to overcome some pressure somewhere. I dunno, I really don't know who to call to come look at this. It's weird, everything else about my shop and house I have people I can call, but no one knows anything about air compressors, and there's really not a company that I can think of that would even come out and look at it, for cheap at least