How much compression should my air compressor pump have?

[That1Guy]

I said goodbye to an old friend today. After 30+ years of working together, through thick and thin, my air compressor motor died right before my eyes. I should have suspected something was wrong when I noticed the breaker was tripped, but no. I reset the breaker and flipped the switch, only to watch as most of the smoke escaped from the motor. As with anything electrical, it's almost always very expensive to put that smoke back in. No indication as to why it gave up the ghost. I guess it was just time. I checked with a local electric motor warehouse near me only to find out, of course, it is a "proprietary" motor and they don't list a direct replacement for it... WTH? So tomorrow I will check with a local repair shop to see if there is any chance of resurrecting the old motor. It's a Baldor so I'm hopeful.

All that said, my question has to do with the compressor pump. Since it's 30+ years old, and currently disassembled because of the motor, I'm wondering if now might be a good time to rebuild the old girl because I don't want to disassemble this monster again any time soon. Plus, I can't afford to have it fail later as I don't have a backup compressor and let me tell ya, you don't realize how much you depend on your compressor until it goes down. I had no idea how often I use that thing - lol.

So, while removing the motor, I gave the big ol flywheel a spin, just because it was there and I'm me, and it turned very easily. Easier than I was expecting actually. I'm not sure what exactly I was expecting, but it felt like it spun "too" easily. I've never spun it by hand before since this is the only time it's ever been apart - lol. So I don't know if it spun too easily or not. I guess I was expecting to feel some sort of compression resistance like a small engine or something. Again, I have nothing to compare to or to reference. Should it turn over without much compression or should there be at least some resistance? It has been working flawlessly without any noticeable lack of performance. I've never timed it to see how fast it comes up to pressure or anything but I haven't noticed it lacking in any way either.

I guess what I'm asking is if there is any way to test it to see if it's due for a rebuild or should I just let it keep doing it's thing until it doesn't? I don't want to throw any money at it unnecessarily, but I also don't want to put it all back together only to have to tear it all back down in a month or two. I don't know what brand of pump it is either since I purchased it from a local tool guy who was sourcing parts and building them to order. He has since passed away so I can't ask him. I also can't look up a rebuild kit to get a guesstimate on the cost of a rebuild either. There may be casting marks that might identify the make and model of the pump but I haven't looked yet. I've been too busy with the motor and I'm in for the night and I'm just now starting to wonder about the compressor pump.

So again, is there a way to "test" the pump or can someone tell me if there should be a noticeable resistance (compression) when I spin the flywheel? Any thoughts, opinions or suggestions are greatly appreciated and thanks in advance for whatever input you might offer. Sorry for the long winded post. It's just me.

 

[The Cobbler]

there should be no resistance when there's no pressure on the pump . it should turn freely.
if you blocked the outlet you would build pressure & it would have compression resistance .
If it was building pressure fine before it should be OK .

 

[Schurkey]

Spin it when there's 175 psi in the tank.

Just like an engine, the faster you spin, the more pressure you produce, as there's less time for the air to leak past the rings.

 

[larry_g]

It has been working flawlessly without any noticeable lack of performance.

This statement leads me to think that you'll be OK with just replacing the motor. As stated above the outlet to the pump is not restricted like in a IC engine so there is little resistance to turning until the outlet is pumping against pressure in the tank. You could plug the outlet with a plug and turn by hand and then you should start to feel resistances on the the second or third revolution. If not then you have opportunities...

lg
no neat sig line

 

[Packard V8]

I checked with a local electric motor warehouse near me only to find out, of course, it is a "proprietary" motor and they don't list a direct replacement for it... WTH?

Very few air compressor motors, even Baldor, are so unique they can't be replaced with an appropriate spec generic motor; horsepower, RPM, shaft diameter, duty cycle and base are pretty standard.

Just don't make the mistake of choosing a "compressor duty" piece of junk with a sheet metal frame, pot metal ends and half the size of the one you're replacing.

So tomorrow I will check with a local repair shop to see if there is any chance of resurrecting the old motor. It's a Baldor so I'm hopeful.

Back in the day, I'd have done the same thing. Today, there's only one electric motor shop in town and they'll tell you, "Don't waste your time and ours; buy a new one."

jack vines

 

[That1Guy]

there should be no resistance when there's no pressure on the pump . it should turn freely.
if you blocked the outlet you would build pressure & it would have compression resistance .
If it was building pressure fine before it should be OK .

Good point. I hadn't thought of blocking the outlet. That makes sense.
And yes, it seemed to build pressure just fine.
Thanks.

Spin it when there's 175 psi in the tank.

Just like an engine, the faster you spin, the more pressure you produce, as there's less time for the air to leak past the rings.

I'm not sure if you're messin with me - lol. The only way to get pressure in the tank is with the motor - the dead motor - lol!
But yeah, I see your point and I agree. I guess I just figured there should be SOME sort of resistance just from the piston rings or something. But considering that big heavy flywheel, it'd probably take quite a bit of resistance to be noticeable.
Thanks for your input.

This statement leads me to think that you'll be OK with just replacing the motor. As stated above the outlet to the pump is not restricted like in a IC engine so there is little resistance to turning until the outlet is pumping against pressure in the tank. You could plug the outlet with a plug and turn by hand and then you should start to feel resistances on the the second or third revolution. If not then you have opportunities...

lg
no neat sig line

Agreed. I'm sure it'll be fine. If not, I'm confident I can break it down in half the time it took the first time - lol.
Thanks for the input.

Very few air compressor motors, even Baldor, are so unique they can't be replaced with an appropriate spec generic motor; horsepower, RPM, shaft diameter, duty cycle and base are pretty standard.

Just don't make the mistake of choosing a "compressor duty" piece of junk with a sheet metal frame, pot metal ends and half the size of the one you're replacing.


Back in the day, I'd have done the same thing. Today, there's only one electric motor shop in town and they'll tell you, "Don't waste your time and ours; buy a new one."

jack vines

Yeah, I think what she meant was that they only carry generic plain jane versions of whatever brand of motor they carry. She said the problem is with differences in shaft diameter, length, single or double shaft, type of base, type of end plate - yadi yadi yadi. Once she started to say all that my eyes glazed over and I didn't hear much else. It all sounded like "no" to me.

And I agree about the low quality "generic" replacements with weak bases and poor fit and finish - hard pass! This motor is a beast and I don't want to settle for less. That's why I'd rather get this one rebuilt even if it cost the same to rebuild this one as it would cost to buy a new china motor. The guy at the shop told me over the phone that this motor is definitely worth rebuilding if it can be. He said they have new ones for sale too but this one is a good motor. I guess we'll see.

Thank you all for your input.
I appreciate the time you guys took to share your thoughts and opinions.
I'll make sure to post back here what ends up happening with my motor.

 

[The Tool Tyrant]

Post a few pics of the pump and someone here will most likely know the manufacturer. As long as it's always had oil changes and the crankcase is not full of water (condensation) and the intake filter maintained, the most you would want to do is a valve job.

 

[Walkers]

Pull the head and look at the cylinders. A new set of gaskets and valves does wonders for aging compressors.

 

[American Locomotive]

And I agree about the low quality "generic" replacements with weak bases and poor fit and finish - hard pass! This motor is a beast and I don't want to settle for less. That's why I'd rather get this one rebuilt even if it cost the same to rebuild this one as it would cost to buy a new china motor. The guy at the shop told me over the phone that this motor is definitely worth rebuilding if it can be. He said they have new ones for sale too but this one is a good motor. I guess we'll see.

Electric motor rebuilding on small motors is only economical if the failure is something minor - like bearings, centrifugal switch, or capacitors. If your motor blew up its switch or capacitor - chances are it will be economical to repair.

If the motor smoked the winding, it's not worth it. Generally motor rewinding is only starts to get economical at the 30+ HP range.

 

[That1Guy]

Yeah, I'm worried about those windings for sure.
I'm really REALLY hoping it was just the caps and not anything serious.

 

[That1Guy]

Post a few pics of the pump and someone here will most likely know the manufacturer. As long as it's always had oil changes and the crankcase is not full of water (condensation) and the intake filter maintained, the most you would want to do is a valve job.

Sounds good. I'll do that. Thanks.

Pull the head and look at the cylinders. A new set of gaskets and valves does wonders for aging compressors.

Good idea. Definitely worth the time and effort to at least look it over. At least that way I'll have peace of mind if everything looks good.
Thanks.

Electric motor rebuilding on small motors is only economical if the failure is something minor - like bearings, centrifugal switch, or capacitors. If your motor blew up its switch or capacitor - chances are it will be economical to repair.

If the motor smoked the winding, it's not worth it. Generally motor rewinding is only starts to get economical at the 30+ HP range.

Yeah, I'm worried about those windings for sure.
I'm really REALLY hoping it was just the caps and not anything serious.

TJ