[justincampbell]

I'm hoping someone here can point me in the right direction.

The air compressor I'm using has, over the last 2 or 3 days of use, been slowing down when it runs. The last time it ran I ended up shutting it off because it was working so hard(started running at only a few hundred rpm and was shaking the whole unit on its pallet).

The only thought I had was possibly bearings in the pump? I took the guard off the pulley side and turned it by hand and nothing felt abnormal to me. I also held onto the pump pulley and tried to wiggle it, but there didn't seem to be any slop. It really confuses and frustrates me because for the last 10 or so years it hadn't been used much. So I drained the tank of any water and changed the oil in the pump because I knew I was going to be using it quite a bit now. And, of course, now is the only time it has ever had any trouble.

The compressor is a vertical 60 gallon, 5 hp 1740 rpm unit. I can find a brand on the motor and a brand on the tank, but not a brand on the compressor as a unit. This was purchased new approximately 40-45 years ago and has always been a super reliable unit... until recently.

Thanks in advance for any help.

[dataway]

Did you try running the motor without the belt to see if the motor was making any noise?

If it's not the motor bearings .... and the flywheel feels normal when you turn it ..... I have seen them break a rod .... if it breaks down low and the remains aren't hitting anything internally they won't make a whole lot of extra noise but will vibrate terribly.

Motor will work very hard and they won't make much pressure.

If it's a Sears or other such store brand with an aluminum pump and rods ... they have a pretty limited lifetime.

[BTCS]

Maybe try disconnecting the discharge tubing at the head and seeing if it'll pump air normally without any back pressure?

[necdb3]

Also check the voltage to the motor while running.

[steve v]

Originally Posted by necdb3

Also check the voltage to the motor while running.

X2
I recall years ago trying to run a table saw off of a 100' extension cord & there was too much voltage drop thru the cord to get the saw to run.

[justincampbell]

Originally Posted by dataway

If it's a Sears or other such store brand with an aluminum pump and rods ... they have a pretty limited lifetime.

It's a cast iron pump.

[justincampbell]

Thanks for the suggestions. Hopefully I'll get and opportunity to go check some of these things over the holiday. The place I am working is over an hour away, but I'll keep you all updated when I have gotten a chance to get back and check it out,
Thanks

[TAKerry]

I have the same problem with mine. It runs on a 220v dedicated circuit. I assumed it was a voltage drop but never checked. I have it hooked up to an extension cord that is about 20' long, may be too small of a guage. I have a table saw that uses the same outlet plugged in direct and have never had a problem.

[justincampbell]

Originally Posted by TAKerry

I have the same problem with mine. It runs on a 220v dedicated circuit. I assumed it was a voltage drop but never checked. I have it hooked up to an extension cord that is about 20' long, may be too small of a guage. I have a table saw that uses the same outlet plugged in direct and have never had a problem.

This is also on a 220v dedicated circuit, but it is hard wired rather than plugged in. It is very confusing as it was wired in almost 40 years ago and has not been altered since... nothing in the building has been changed in that 40 years. Seems odd that there was never a problem until now.

[dataway]

Simplest first check would be pulling the cover off the pressure switch and checking for good power ... should have 110-120 VAC between each of the hot wires and the neutral, or 220-240 VAC between the two hots. Someone correct me if I'm wrong.

[justincampbell]

Had a few minutes today(not near as long as I had hoped unfortunately). I'm even more confused now. I bled the tank down to about 25 lbs of pressure and then turned the compressor on. It ran like a champ. I shut it off manually at about 120 lbs. After 15 or 20 seconds, I turned it back on and it ran like a champ again all the way to it's preset shut-off pressure(160-ish lbs).

[dataway]

In that case I'd say it was an electrical problem. Could have been something in the motor start system ... other people here would know more ... but that looks like a nice capacitor start motor ... I know it's got some mechanicals in it, contacts and such, could have been dirt, mouse house, etc. specially if it's been dormant for a long time.

Also ... using it under pressure, and having it cycle numerous times under pressure puts a lot more load on it than running up to pressure once.

But, sounds like it's not a pump problem ... they don't just go away.

[bluebandit]

Could be the start or run capacitors are going out on you.

[justincampbell]

The garage has gotten quite damp/humid in the past. Could some sort of corrosion in the electrical be the problem? Or would that also be consistent trouble rather than hit and miss?

[dataway]

That would be as good a cause as most I can think of. 40 years is a LONG time for any big AC motor to go unserviced and uncleaned.

I've got equipment here that has large AC motors ... apart from keeping them clean I don't know much about fixing them.

That looks like a decent quality old school compressor, worth saving if the motor just needs servicing and the tank is not too rusty inside.

And I'd say yes, that corrosion could create an intermittent problem like that, that might go away with more consistent use ... but it's going to come back at some point.

There are usually local places that will clean and service AC motors like that ... you'd have to remove it and take it to them though.

[daduck]

It may not be the Air Compressor at all.

I suspect you lost one of the phases at the circuit box. 240 VAC is just 2 each 120 VAC lines at different phases and when you loose one leg the 240 VAC device (in this case your compressor) will run very slow or not at all.

So if your local power company had a temporary interruption of one of your 120 VAC feeds to your circuit box...….....that could explain why it started working again.

This is not uncommon in the Power Distribution business.

[daduck]

It may not be the Air Compressor at all.

I suspect you lost one of the phases at the circuit box. 240 VAC is just 2 each 120 VAC lines at different phases and when you loose one leg the 240 VAC device (in this case your compressor) will run very slow or not at all.

So if your local power company had a temporary interruption of one of your 120 VAC feeds to your circuit box...….....that could explain why it started working again.

This is not uncommon in the Power Distribution business.

[justincampbell]

Thanks for all the replies. I guess I'll just try to ensure that everything is clean and wait to see if the trouble starts again at some point. Then go from there.

[Simple Man]

My compressor starts and runs slow when it's cold out. The belts are old, and you can smell them slipping.

[T.Weber]

Is the compressor unloading the pressure line from the tank to the compressor head every time it stops? If your unloader is sticking open the compressor will start or try to start under full load pressure.