Air compressor question?

[1BAD68]

I'm not sure where to find the info I need so I'll start here.
I have a really old two stage compressor that runs off a 220V 1710 rpm motor. It barely keeps up with a 16" inline sander.
The drive pulley is 4" and the pump pulley is 13" which equates to the pump being driven at 526 rpm.
If I switch to a 5" pulley the rpm's will be 657 and a 6" pulley will put it at 789 rpm's but I dont want to burn this thing out.
Its a 1947 Westinghouse pump.
I'm wondering how can I find out the max rpm's I can drive the pump?

[Todd Wilson]

Short of finding the specs for the 1947 pump I dont know how you could tell.  If its like anything else old from that era  its bullit proof but you dont want to push it past what its meant to turn at.


Todd

[ih8gmandford]

 What HP is your motor? Has it ever kept up with your tool requirements? The old recip compressors were made to run at a lower rpm for proper splash lubrication. Running them at a higher rpm will possibly cause more mist than a splash, causing bearing wear and cylinder wall scuffing. Ya ever try to get 40+ year compressor cylinders or oversize bearings? Not easy!
  I work on air compressors and systems for a living. I wouldn't swap the pulley. If you do, I would consider going to a thicker compressor lube.  -Jason

[bobs66440]

How many gallons is the tank? Volume is the key to running air tools. The bigger the tank, the better. 60 gal. or bigger should do it. I had a 30 gal. 5hp compressor and it just couldn't keep up.

[1BAD68]

Its a 60 gallon and I'm not too worried about oil because its pressure lubed.
Most of the two stage pumps I've seen online are rated between 550 and 1050 rpms so I'm guessing 789 rpm's would still be within specs.
It keeps up with most tools except the inline sander so just a little bit faster would be nice.

[69 OUR/TEA]

Did you ever consider that the compressor(pump)being 63 years old,has seen better days?And needs a rebuild in the piston and rings department,and is why it is not keeping up,therefore speeding it up might not be the answer.

[ih8gmandford]

 Your compressor will deliver about 4cfm per hp. If you are not running a pressure regulator on the tank's outlet, I would look into installing one. Air tools are meant to be ran at approx. 90 - 100 psi. By bumping up the pressure on the tank (135 online, 150psi offline), you will be increasing the volume of air stored in the receiver. The regulator kicks down the pressure to whatever you adjust it to - your sander mfg. should be able to give you this pressure. Any more, and you're just wasting air.
I can provide a pump-up test time if you send me your compressor HP, receiver size, and what pressure you run it to. This is a pretty good method to calculate your unit's working condition.
If you do decide to swap the pulley, check your amp draw. If you're gonna try to get 7 hp of work from a 3 hp motor, it's gonna draw hard into the motor's service factor. The higher the pressure, the worse it gets... -Jason
 

[Cooter]

It's prolly a question of Volume and NOT speed of the motor/compressor...If it won't keep up there's isn't enough volume..

I would try and plumb in another tank inline with the 60 gal tank so you double your volume...

[Todd Wilson]

I have 2 compressors hooked together. 50gallons total.  Having one compressor on  it would run my air file just fine but would not run the DA. Had to fire up both for that.



Todd

[1BAD68]

Your compressor will deliver about 4cfm per hp. If you are not running a pressure regulator on the tank's outlet, I would look into installing one. Air tools are meant to be ran at approx. 90 - 100 psi. By bumping up the pressure on the tank (135 online, 150psi offline), you will be increasing the volume of air stored in the receiver. The regulator kicks down the pressure to whatever you adjust it to - your sander mfg. should be able to give you this pressure. Any more, and you're just wasting air.
I can provide a pump-up test time if you send me your compressor HP, receiver size, and what pressure you run it to. This is a pretty good method to calculate your unit's working condition.
If you do decide to swap the pulley, check your amp draw. If you're gonna try to get 7 hp of work from a 3 hp motor, it's gonna draw hard into the motor's service factor. The higher the pressure, the worse it gets... -Jason
 

I did the calc's to find the true CFM of my compressor - 6.7 CFM @ 90 psi
The regulator is set to kick on at 100 psi and off at 120 psi
It has a 1.5hp 220V motor, 60 gal. tank.

[Todd Wilson]

If thats the picture of it it appears to be a nice old unit. Super slick old compressor but look at the pump. Thing in the picture appears to be super small compared to todays 220volt compressors. Heck even 110 compressors. I'd keep it and use it for what it is and not try to push the pump any.



Todd

[elacruze]

Ok now here we're going to get into a little more fun with physics.

Your motor is rated at 1.5hp *at a given amperage* at 220vdc. <edit> Oops, volts AC. 

Without an amp meter, you don't know how much resistance the compressor is putting up. The thing is, electric motors operate at a static RPM, so you can't tell how much work they are actually performing without knowing the current they consume.

So!

Once you know the amperage at which your motor is rated (which on such an old motor will probably be on the data plate) Then you can use an amprobe to determine the current draw at a given pressure (remember the compressor will require more HP per RPM as pressure/resistance goes up) Once you know the pressure at which the rated HP current is achieved, then you can set your motor up for most productive work cycle. If your compressor does not reach 1.5hp current before 150psi, you could increase the RPM of the compressor up to the point that your current level is reached. You can also increase the RPM of the compressor more if you reduce the cutout pressure of the regulator so that your specified current is not breached.

Make sense? At 90 psi the compressor may only force the motor to draw .8hp worth of current so you could increase RPM by 50%, giving a dirty measure of 1.2hp current. If you increase RPM by 50% and reach your 1.5hp current at 125psi, set the regulator to cut out and in at 125-95 and you're good to go with 50% more capacity.

Hurt yet?

Of course, none of this addresses the mechanical stresses on the compressor itself, only the motor.

[bobs66440]

Ok now here we're going to get into a little more fun with physics.

Your motor is rated at 1.5hp *at a given amperage* at 220vdc.

Without an amp meter, you don't know how much resistance the compressor is putting up. The thing is, electric motors operate at a static RPM, so you can't tell how much work they are actually performing without knowing the current they consume.

So!

Once you know the amperage at which your motor is rated (which on such an old motor will probably be on the data plate) Then you can use an amprobe to determine the current draw at a given pressure (remember the compressor will require more HP per RPM as pressure/resistance goes up) Once you know the pressure at which the rated HP current is achieved, then you can set your motor up for most productive work cycle. If your compressor does not reach 1.5hp current before 150psi, you could increase the RPM of the compressor up to the point that your current level is reached. You can also increase the RPM of the compressor more if you reduce the cutout pressure of the regulator so that your specified current is not breached.

Make sense? At 90 psi the compressor may only force the motor to draw .8hp worth of current so you could increase RPM by 50%, giving a dirty measure of 1.2hp current. If you increase RPM by 50% and reach your 1.5hp current at 125psi, set the regulator to cut out and in at 125-95 and you're good to go with 50% more capacity.

Hurt yet?

Of course, none of this addresses the mechanical stresses on the compressor itself, only the motor.

Huh? You lost me after the "physics" part.  

[69 OUR/TEA]

Your compressor will deliver about 4cfm per hp. If you are not running a pressure regulator on the tank's outlet, I would look into installing one. Air tools are meant to be ran at approx. 90 - 100 psi. By bumping up the pressure on the tank (135 online, 150psi offline), you will be increasing the volume of air stored in the receiver. The regulator kicks down the pressure to whatever you adjust it to - your sander mfg. should be able to give you this pressure. Any more, and you're just wasting air.
I can provide a pump-up test time if you send me your compressor HP, receiver size, and what pressure you run it to. This is a pretty good method to calculate your unit's working condition.
If you do decide to swap the pulley, check your amp draw. If you're gonna try to get 7 hp of work from a 3 hp motor, it's gonna draw hard into the motor's service factor. The higher the pressure, the worse it gets... -Jason
 

I did the calc's to find the true CFM of my compressor - 6.7 CFM @ 90 psi
The regulator is set to kick on at 100 psi and off at 120 psi
It has a 1.5hp 220V motor, 60 gal. tank.

1BAD68,I don't know how much you need/use a compressor,and understand money does'nt grow on trees and you are trying to make do with what you have,but if your calcs are right,6.7 CFM @90 is very weak in the compressor world,and that was when it was new.You can get yourself into a new 60gal compressor for low $400's that will outdo the one you have now by a noticable amount(CFM).And if you step up to the $700-800 range and get a 80 gallon the numbers go up to in the 15,16 CFM.I have had one now for around 13 years,Coleman from Sams Club,6.5 HP,2 stage 80 gallon,16.7 @ 40,and 15.6 @90.Runs pretty much anything I attach to it,even runs 2 da's at the same time.Think it went for around $700 at the time.Before you invest into pulleys,and find out they did'nt bring you up to what you were expecting,you might want to do some thinking of a new unit.

BTW,you like the air inline sanders??

[1BAD68]

Ok, the data tag says 6.83 amps.
It draws 12 amps for a second on startup and then runs at approximately 3 amps until it kicks out. I thought it would increase as presuure increased but it doesn't.

69 OUR/TEA, I dont really use my compressor much but I'm doing some minor bodywork and thats how this all started.
Also, why do you ask about the inline sander?

[69 OUR/TEA]

Maybe its me,but I don't care for them,never use them.Anything for bodywork for me is always DA's,or blocking by hand with whatever blocks fit the need.

[elacruze]

Ok, the data tag says 6.83 amps.
It draws 12 amps for a second on startup and then runs at approximately 3 amps until it kicks out. I thought it would increase as presuure increased but it doesn't.

69 OUR/TEA, I dont really use my compressor much but I'm doing some minor bodywork and thats how this all started.
Also, why do you ask about the inline sander?

Well, you can theoretically run the compressor twice as fast without threatening to overload the motor. Obviously, it's not working very hard. Compressor speed is another matter, let your conscience be your guide. As others have pointed out, it may not be very efficient any more. If you haven't already, maybe take the heads off and see what mung has collected on the valve seats etc. You may be surprised at what's in there holding valves open and clogging ports. Paint, oil, and dust make a nasty mix.

[1BAD68]

I pulled the heads and valves and found a lot of gunk, this picture shows where the intake valve on the 1st stage head sits.
You can see that it was full of gunk, there's a 1/2" space around the valve for air to flow thats filled with junk.
After cleaning them up the cycle time is pretty much the same but it's a lot quieter when running now, so I'm going to swap a 6" pulley and see what happens.

[1BAD68]

.

[ih8gmandford]

 What's the cylinder bore look like? Curious because of the oil(?) on top of the piston. It's a pretty good indication of a restriction on the LP (low pressure) inlet side causing the piston to pull oil past the rings, or possibly worn rings. Oil won't do your bodywork any good.
I may have some piston rings and possibly valves for that compressor. Measure the bore size and get back to me if you're interested.
IMO, I would jack the pressure setting on the pressure switch to 165psi offline and a cut-in of 130psi. Set the regulator valve to 95psi. Your compressor will run a little longer, but you will have more cfm in storage. This should give you more of a buffer from the pressure drop and the tool lugging. Here's how it works, to the best of my ability to explain it:
 Let's say, for the ease of math, that your receiver tank is 100 cubic feet. For every atmosphere (14.7psi) of air you force into it, you will get 100 cfm of air. So if your air tool needs 10cfm @95psi to operate, and your compressor doesn't start until 95psi, you will not keep up at all. Instead, you run an additional 60 psi (4 atmospheres) into the receiver tank, giving you an additional 400 cfm of air in reserve before you hit the 95psi performance drop. The pump kicks on at 125psi, giving the compressor a jump on the demand and the ability to use it's running air and the reserve in storage to keep up with demand. At that point, you have the 6cfm the compressor is making running, plus the 200 cfm cushion of the additional 30 psi. You MUST regulate the pressure down to take advantage of this, as the tool will gobble more cfm at a higher pressure, but not really deliver any better performance. The regulator allows the cfm cushion to expand into more cfm at a lower pressure.
 This would be the best way to go. Just check the tank and see what it's pressure rating is. Check your safety valve, too. Much better than killing your compressor by overrunning it for 1, maybe 2, cfm tops.
 If you have more compressor questions, and don't mind long winded answers, I'll take 'em! If you need compressor parts, or possibly that pulley you are thinking about putting on, I can possibly help you there, too. -Jason    

[1BAD68]

Ok I switched to a 6" pulley and checked the amp draw. It pulls 12 amps at start up and just under 6 amps when running, interestingly it only cut about 10 sec. off the cycle time.
Dont feel good about that so I went back to the 4" pulley.
I think you're right about the LP restrictiction because the bores look great with no ridge at the top and the picture I posted shows how restricted the low pressure intake valve was, you wouldn't believe all the junk I cleaned out of it.
I'm going to run it awhile and pull the head to see if there's still oil getting past the rings. The tank say's "Max. allowable working pressure is 200lbs" which I'm assuming is 200psi?
Thanks for the info Jason, I'll set the pressure cut-in cut-out like you said and give it a run.

[ih8gmandford]

Ok I switched to a 6" pulley and checked the amp draw. It pulls 12 amps at start up and just under 6 amps when running, interestingly it only cut about 10 sec. off the cycle time.
Dont feel good about that so I went back to the 4" pulley.
I think you're right about the LP restrictiction because the bores look great with no ridge at the top and the picture I posted shows how restricted the low pressure intake valve was, you wouldn't believe all the junk I cleaned out of it.
I'm going to run it awhile and pull the head to see if there's still oil getting past the rings. The tank say's "Max. allowable working pressure is 200lbs" which I'm assuming is 200psi?
Thanks for the info Jason, I'll set the pressure cut-in cut-out like you said and give it a run.

  I was looking at the pic, and are you sure it's a pressure lubed unit? I see the centrifugal unloader in the front, but no indication of a oil pump. Since you're not over-running the pump, it should still be OK.
Tank is rated at 200psi, so 165 is OK. Just check the safety valve (brass, on the tee on the front of the tank) to make sure it is 175psi. Also, the extra pressure will cause more condensation in the tank, so drain it daily. -JAson

[Todd Wilson]

What is the required psi to run your air tools?  If they are lower and you can adjust your regulator you might be able to lower your PSI down to match that of your tool and be ok. You are having a volume problem. May come down to the compressor is what it is and nothing more. Thats usually the case for very old things. Like I said in my first message. It will do what it will do  but dont push it.
Pulling more amps its cossting you more $$$ to run it now too!

Todd

[1BAD68]

Mainly I want it to last thats why I went back to the 4" pulley, it lasted this long with that pulley.
As far as being pressure lubed, thats a good question. I saw somewhere on the net that these WABCO pumps are press. lubed so thats what I believed mine to be but could be wrong, how can I tell for sure?
And the relief valve... I'm glad you mentioned that, look at the pics and tell me thats not a little scary?

[1BAD68]

 

[ih8gmandford]

 Yikes! Looks like it's looking for an excuse to blow off... hopefully through the roof and not someone's skull! If that's a 110psi safety valve, and you have 145psi in the tank, the valve is junk. Try to find one that's rated at 175psi - they're fairly cheap ($10 or so) and you MUST have one.
Knowing if the pump is pressure lube or splash lube isn't easy unless you are willing to pull the pump apart. The front plate appears to be a centrifugal unloader to allow the unit to run unloaded until up to speed. The oil pump may be mounted in the cover too, but I'm not sure how. EVERY pressure lube unit that I have worked on has a oil pressure gauge on it, and they will usually have a hydraulic unloader instead of the centrifugal one. That's how the Quincy and Speed Air pumps are, at least.
I'm not a fan of the sweated copper pipe for a discharge line, either. I always use black pipe or refrig grade copper tubing bent into shape w/ compression fittings. Just my preference, though. -Jason

[Todd Wilson]

I dont think I would want your set up to put more then about 120lbs into the tank. Glad to hear you went back to the old pulley. That old unit will run forever if you leave it alone and dont push it! I love old equipment like that! If the WABCO is the same WABCO thats on the railroad thats a Westinghoue Air Brake company compressor.

They basically designed the air brake system on trains.


Todd

[elacruze]

Ok I switched to a 6" pulley and checked the amp draw. It pulls 12 amps at start up and just under 6 amps when running, interestingly it only cut about 10 sec. off the cycle time.
Dont feel good about that so I went back to the 4" pulley.
I think you're right about the LP restrictiction because the bores look great with no ridge at the top and the picture I posted shows how restricted the low pressure intake valve was, you wouldn't believe all the junk I cleaned out of it.
I'm going to run it awhile and pull the head to see if there's still oil getting past the rings. The tank say's "Max. allowable working pressure is 200lbs" which I'm assuming is 200psi?
Thanks for the info Jason, I'll set the pressure cut-in cut-out like you said and give it a run.

Glad my math was close, anyway. Curious, what's your cycle time?
If the working pressure is good to 200psi, definitely follow Jason's lead and get the pressure up. Maybe the extra speed just isn't supported by the ports and valves well enough to increase the volume at the same rate as RPMs.