Compressor Pulley Size?

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  #1  
Old 01-17-05, 12:28 PM
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Compressor Pulley Size?

Two stage compressor has a 13 3/4" pulley....

New motor turns at 1740 RPM....

What size pulley do I put on the motor to make the compressor turn at 1,000 to 1,100 RPM?

A friend of mine bought 2 rebuilt compressors out of jet drills from the mining industry. I guess his motor is sounding rough so he wants to replace it with the 1740 RPM.

Is there a formula for this somewhere?

Thanks,

Baldwin
 
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  #2  
Old 01-17-05, 02:18 PM
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OK, found a belt and pulley converter here:

http://www.csgnetwork.com/pulleybeltcalc.html


It says a 8" pulley would turn the compressor at 1010 RPM.

With a 8" pulley on the motor and a 13.75" pulley on the compressor, wouldn't this reduce the power too much from the motor, like driving your car in 3rd gear?

I see the compressor motors in the Northern catalog all turn at 1740 RPM.

Baldwin
 
  #3  
Old 01-17-05, 02:56 PM
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Baldwin,

If you take the 8" for the motor pulley and divide it by 13.75" for the flywheel you get .59 which is the pulley/flywheel ratio.
Multiply .59 times the 1740 motor rpm to get 1026 compressor rpm.

You need to be carefull when changing motor types because often the hp rating of the replacement is a bit off.
You need to use a clamp on ammeter to check the motor amps just before the pressure switch opens which will be the maximum load.
 
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Old 01-18-05, 10:17 AM
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So, that's how you figure that. Thanks!

I don't know the horsepower of the motor he has on there now, I think this is the motor he wants to buy:

http://www.northerntool.com/webapp/w...issearch=16154

About the only thing he uses it for is blowing grass off his lawnmower. He's retired and likes to tinker with stuff.
 
  #5  
Old 01-18-05, 11:01 AM
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That's one chunky looking motor.
I would sure like to have that one.

Whether it's the right one no body would be able to know.
We don't have near enough info.
If he is replacing a 3400rpm (or so), 56 frame motor with this one then he may even have trouble fitting it on the base.
Not to mention the cost of the large bore pulleys you would need to buy and experiment with.

Right now this is really a guessing game and we need to know the intimate details of what we are working with.
You don't even say for certain that the old motor is even 3400 rpm.

Here is what needs to be done to not have to reverse engineer this.

You must go to the manufacturers literature and find the EXACT model of compressor head he has.
They will then have tables for this particular model of compressor head that shows the cfm capacity, rpm required to achieve this capacity and the hp it takes to do it.
These charts are for industrial rated, 100% duty cycle motors which is what you linked to.
The hp ratings of 3600 rpm, consumer motors are in a class of their own having more to do with misinformation than a measure of power.

Punch in the make of the head into Google and change the search terms 'till you come up with this info from the mfr.
 
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Old 03-03-05, 01:41 PM
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Slight delay, my friend had shoulder surgery.

Here is some info from the engineering data sheet he had:

Bore: 3" & 1 3/4" Min RPM: 350 Max RPM: 1015
Sheave OD: 13.75" Sheave PD: 13.38" (what's that)

Ingersoll Rand Model # 234x2

Performance:

1.5 hp....125#....690 RPM....6.1 ACFM....1.7 BHP
2...........125......885..........7.3.............2.2
3...........125......1015.........8.3............3.1

I talked to an Ingersoll guy in Minneapolis, he said the x2 means 2 hp. but he can install a 5 hp if he wants, just don't exceed the 1015 RPM (3.5" pulley on a 3600 rpm motor should work.)

So, I talked him into this slightly smaller motor:

http://www.northerntool.com/webapp/w...ssearch=162492

Question:

I can't find any information on a 56HZ base motor. His bolt slots are 5 1/2" apart. Will this work?

Thanks,
Baldwin
 
  #7  
Old 03-04-05, 09:11 PM
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Baldwin,

That motor will be fine.

The 56 frame designation refers to the physical size of the motor housing but the bolt pattern often varies.
It is normal to sometimes have to drill the base of the compressor to fit the motor.

3.5" pulley would be correct.
 
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