compressor killing motors

[rutbeer]

Probably not the right forum to ask this, but thought I would give it a shot. I have an old compressor, runs on 220v, but it's been heavily "modified". The previous owner put a 3 cylinder 2 stage head on it. It's a speedaire unit, but I don't have the model number in front of me. Anyway, it's never run right. It will fill the tank fine the first time, then smokes the motor after two restarts. The motor on it now is the original Craftsman 2hp one. I bought a 6.5 horse motor and ran it that way for a few hours....and smoked that motor too. It would turn, but barely, and with no torque. So what gives? I know it's dumping air, I can hear the unloader working. I have rewired the whole thing with new wire and all of that heavy gauge. The original 2hp has finally given up the ghost and won't even last one cycle now.

 

[-Spike-]

I'd guess it needs a bigger motor or a smaller drive pulley, but I don't know what I'm talking about. Does the pump turn easily by hand?
I'd take it to a local guy who fixes them, see if he thinks the motor or pulley is up to the task, or if there's something else to look at.

-Spike

 

[sixty]

That 6.5hp motor does not sound like a true 6.5hp, probably 2 or less. Look for a good motor, larger than 2hp and it should fix your problem. The plate on the pump should tell you the hp and rpm's it requires. A smaller pully on the motor may also fix it, but limit the output. some pumps have min rpm's also.

 

[Wile E Coyote]

Before you damn the motor being mismatched, check the power supply it's plugged into. An easy way to kill a motor is through 'brown out' aka undervoltage. Don't know the minimum voltage # off hand for 220/240v motor, but let's say roughly 200v or less until someone smarter than me pipes up.
You aren't perhaps hooking up to a recept. with one dead leg= 110v?

 

[rutbeer]

Not a chance on the line being dead. It's done it on two different houses. I measure 110 at each leg and that same circuit powers my 220 plasma and 220 MIG just fine.

That 6.5 horse was an SPL motor. It ran great for a while, but the sandblaster killed it in about 3-4 hours of work.

 

[Wile E Coyote]

Not a chance on the line being dead. It's done it on two different houses. I measure 110 at each leg and that same circuit powers my 220 plasma and 220 MIG just fine.
.

Fair enough, but don't rely only on the plasma or the MIG as good benchmark loads for that circuit (moot point...I know you measured it, this is kinda a nitpicky FYI) they aren't nearly as sensitive to line voltage as a motor would be.

 

[rutbeer]

Really? I know the plasma will run on any voltage, but the mig seems to be sensitive.
But yeah, I checked that. What's so strange is that from cold it will run and completely fill the tank without issue. It's the restart at 80psi or so that gets it. You would think that there is pressure on the head or something, but you can turn the compressor wheel by hand. To verify no pressure at the head, I disconnected the feed and no air escaped....so the one way valve and the unloader are working properly. I pulled the 2hp motor and took it into a motor shop, fully expecting them to tell me the capacitor was shot....but they didn't find anything wrong with it.

 

[Wile E Coyote]

Yes, really...Think about what the welder does to line voltage to obtain welding voltage. Drops it to roughly 20v, right? Now, this does not mean a 220v welder would be happy at 180v or so, but you get the idea. It still has voltage parameters, just not nearly as tight as an AC motor.
Sidetrack ya enough? Wish I coulda used that minute of your life to fix your problem, but I'm lost from here on, hehe.

 

[D'Animal]

Make sure you get a motor that is rated for an Air Compressor.

 

[FJ40Jim]

The motors must be getting hot and losing power. If brownout is not the problem (check line voltage into the motor when running), then the compressor is putting too much load on the motor, right?

Maybe try a smaller diameter pulley on the motor. I recently rebuilt my vintage compressor. Couldn't find the right motor pulley, wound up with one that is a size larger. Now the compressor spins like crazy, makes the motor get hot, but doesn't actually pump any more air. The local compressor tech says that there is an ideal speed for the compressor where it is most efficient. Above that, the compressor pistons flail about, but don't have time to shove much air through the valves.

GL

 

[Dirtsquirt]

your unloader isnt working (most likely)

The pump you have there is Champion (mfg)
depending on bore there are 3 units identical cept the bore

My initial though is your unloader isnt working.
When it shuts off that 1/4 line that tees into the
discharge line of the compressor output. Should dump the air in the big 1/2" line when it shuts off.. .
should go psssssssssssssssssh and quit exhausting air.
edit here. reread initial post. it sounds like it is unloading. I would now ask does it stop dumping air. or does it continue to bleed air till it restarts..
if the bleeding continues till it starts again. you have a bad check valve.

Other isssues that bother me at this point is. are you under motoring the unit..
Model number of the pump itself would be nice..4Z855 (example)
and the name plate data on the motor HP, Rpm, Service factor
SF, pulley dia on motor..
All would help me help you.

the tank you have there originaly came with a Campbell hausfeld compressor. It possible your pulley combination is
such as you are overworking the motor.
supply the above requested info and I can tell you where you stand

I was a service tech on comnpressors for 10 years. this is a standard set up.

Lemme know it likely i can help if you feed the data

 

[rutbeer]

I'll look up the data on it. I can answer a few items off the top of my head though.

The compressor is originally a "craftsman" unit made in the 60's or 70's. The original manufacturer for craftsman is listed on it, I'll get that info too.

The unloader and check valve both work that I can see. After it runs, goes ssssttttt, then it stops. I actually disconnected the copper feed line just to see if it still had pressure in it. It did not.

 

[Dirtsquirt]

yup

sounds like it it unloading and the check valve is good
Craftsman makes no tools directly there are all made for them
Rebadged.
The tank you have there is a sears compressor Manufactured by
campbell hausfeld.. the original pump was most like a 2 cyl siamese
Or possiblly the rare 2 cyl V pump of which there are no parts for.
Neway.. motor pulley , rpm, sf, is in order now

 

[rutbeer]

Tank: Melben Products Co., Inc. Harrison, OH. 163psi working pressure.

Motor: Craftsman 2hp. 115/230v 60hz, 24.8amp, 3450rpm, SF 1.0, SFA 24.8/12.4 continuous duty, and running about a 5" pulley.

Compressor head: Speedaire by Dayton Model number 3Z176B Pulley size 12.5"

 

[Dirtsquirt]

Heres the deal

Your motor pulley would be right if your motor was 1725 rpm
and you motor had a SF of 1.15

your gonna have to buy a smaller motor pulley. Half the dia. would be ok
but I would go slightly less. 15% less than half.

Compressor motors as a rule have a 1.15 or greater SF
this allows the MFG. to squeek out little more air by using that
SF

Not sure how much damage has been done but a motor pulley change will get Where you should be.

here is a link to the compressor Pneumatics & Hydraulics > Air Compressors and Vacuum Pumps > Air Compressor Pumps > Pump,Compressor : Grainger Industrial Supply

 

[rutbeer]

You are the man...I have been looking for info on that compressor head for 6 years. Don't know why searching on the model number didn't turn it up before now, but sweet! Wow...$800 compressor head. And I was worried that I spent too much on it when I bought the whole deal for $155.

Okay, since you are the whiz, what's it mean when it first starts up on an empty tank and there is a "knocking" sound from the compressor head for first two seconds? As soon as it hits full rpm, it sounds normal....but early it's almost like wrist pin knock.

 

[Dirtsquirt]

You could be right

and you could be wrong..
It could also be your check valve hammering and resonating in the tank.
stick a screwdriver up your ear and press it against the tank
is the noise there?
or is it more predominate on the little cylinder of the 3 in the area of the wrist pin.
If it is the wristpin I would tear that baby down b4 it does irreprable damage.
you break 1 rod in that and you are gonna break all 3..

I'm gonna say its greater probability that is is the checkvalve.

You can remove the check valve and take the spriing and seat out of it.. hook it all back up and start it .. if no noise with no spring and seat.. it definately is the checkvalve.

 

[rutbeer]

I put about a 2.75" pulley on it tonight and ran it. The hammering was gone, and it runs amazingly quiet now. It does take at least twice as much time to fill the tank from zero, but it doesn't seem to have a problem straining at the load like it did. I'm going to run it fairly hard tomorrow with a paint sprayer and see what happens. It seems too quiet to me though....I'm not used to a compressor not being very loud. I almost think, by ear only, that it needs about a 3.25" or 3" pulley on it. Just a touch faster is all.