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Tool Talk Discussion Forum

Pulley/Gearing ratios???

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Trucks

12-31-2004 16:39:52

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Hi guys, I was wondering if anybody out there has any ideas on how to calculate the speeds of pulleys and such to achieve a certain RPM???Please help me.I am trying to get enough power to run a VERY BIG air compressor.I can't afford a big enough phase convertor for the job.It has a good motor on it.It is 25HP, but it doesn't have to turn very fast, and I was thinking if I could get a very large(24") flywheel and mount it on a shaft on a set of pillar block bearings, then I could maybe gear it correctly to get the right RPM.The compressor has a 24"flywheel on it, and the motor has a 12"pulley on it.The motor turns 1750RPMs.The compressor should turn 1150RPMS at the fastest or 400 RPMS at the slowest.Thanks in advance if anyone can help.

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trucks

01-01-2005 13:37:02

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Re: Pulley/Gearing ratios??? in reply to Trucks, 12-31-2004 16:39:52

Hi guys, the brand name of the compressor is Quincy (as if there is any other brand)it is a 5120 model.I was hoping for like the one cat said a magic jackshaft kind of setup.I was hoping to maybe get by with the maximum of a 10hp single phase 220v motor.I originally was going to try to put a 10hp motor between the 25hpand compressor and put a 5 or 6" pulley on the 10hp using it to turn the 25hp motor for an idler or jackshaft.Is that even possible, if not I guess I'll have to sell this BEAST.I don't want to.I thought about putting an old 302 FORD on it, as I'm a big Ford man.(My 1956 F-100 is in Classic Trucks magazine this month page 85)

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Roger P.

01-01-2005 14:11:33

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Re: Pulley/Gearing ratios??? in reply to trucks, 01-01-2005 13:37:02

Oh yeah, I remember this one now. As you will most likely be able to use 10hp maximum out of that compressor with a single phase motor (with a very heavy amp load on startup), why not trade it off for a good 10hp, like a DeVilbiss 445/DeVair 447, Kellogg 452, Quincy 340/350, or an older Ingersoll Rand Type 30. That 5120 is about $6000 to buy brand new as a bare pump. If it were me, I think I'd trade it off for something more suitably sized, just my opinion. You could post it with compressorworld.com and see what you could get for it.

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01-01-2005 12:57:46

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Re: Pulley/Gearing ratios??? in reply to Trucks, 12-31-2004 16:39:52

Looks like you now have a 2/1 ratio which should have your compressor now turning at 875 rpm. Whether single phase or three phase it is still going to take 25 hp to turn the compressor. Going to take some pretty substantial wiring to turn 25 hp on single phase. Might want to use a gas engine or your tractor.

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Roger P.

01-01-2005 12:05:15

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Re: Pulley/Gearing ratios??? in reply to Trucks, 12-31-2004 16:39:52

I am curious now, do you know what type of compressor pump you have? The only one that springs to mind right away with such a large flywheel is a Kellogg 462.

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deadeye

01-01-2005 07:50:28

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Re: Pulley/Gearing ratios??? in reply to Trucks, 12-31-2004 16:39:52

I have a couple of websites I go to for various info like that. Here is one of them if I can get it attached.. deadeye

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deadeye

01-01-2005 07:57:43

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Re: Pulley/Gearing ratios??? in reply to deadeye, 01-01-2005 07:50:28

Here it is, try this. Link

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Butch(OH)

01-01-2005 07:44:48

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Re: Pulley/Gearing ratios??? in reply to Trucks, 12-31-2004 16:39:52

Not to be arguementitive,, well I guess I am, a 3" O.D. pulley on a 25HP motor? That's a laugher Ryan, a 25HP motor if it is a T or U frame will have a 1 5/8 shaft. He isnt going to get a 3" pulley to fit it and wouldn't want it if he could because there is not enough belt contact surface to transmit any power. A 52" pulley? You haven't bought any big pulleys as of late I take it? The pulley on an air compressor is also the fly wheel, you dont put a stamped sheetmetal combine pully on an air compressor. He owns a 24" pulley on the compressor and can achieve a ratio that will run the compressor at the slowest speed it can operate with a motor pulley (5.5") that falls well within general engineering guidelines for such. Why would he want to trash the compressor pulley he allready owns and buy two high dollar pulleys when he can buy one? Maybe I missed something in The Original question? Mr. Trucks, If your need to run that compressor shaft at 400 RPM minumum and you can do it by purchasing one pulley, a 5 1/2"er for your motor and run the V-belts over your 24" fly wheel whether it is flat faced or grooved makes no differance. There is no magic in multible jack shafts for doing what you want to do. Put 10 jack shafts inbetween them if you wish, it is still going to take the same amount of torque at the driver(motor) shaft to turn the compressor at 400RPM..

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buickanddeere

01-02-2005 19:03:42

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Re: Pulley/Gearing ratios??? in reply to Butch(OH), 01-01-2005 07:44:48

Another problem with the jackshaft is that 6-8% of the power going through each belt is going to wasted as friction/heat.

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Ryan -WI

01-01-2005 06:32:14

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Re: Pulley/Gearing ratios??? in reply to Trucks, 12-31-2004 16:39:52

TO answer your original question.

Assuming you do not change the pulley on the motor...

You want a pulley between 18.2 and 52.5 inches in Diameter.

The 18.2 will make the compressor turn at 1150 and the 52.5 will make it turn at 400. Any pulley size in between will make it spin somewhere in the middle.

If these sizes are too big you can do the same thing with smaller sizes by dividing the diameters of both pulleys (motor and compressor) by the same number. For example if you divide both by 4 you would put a 3 inch on the motor and that would allow you to use between a 4.5 and a 13.125 on the compressor and still get the same rpms.

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Rod (NH)

12-31-2004 19:14:50

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Re: Pulley/Gearing ratios??? in reply to Trucks, 12-31-2004 16:39:52

Hi Trucks,

It's just the ratio of the pulley diameters. For example:

D1 x RPM1 = D2 x RPM2

Where D1 = diameter of drive pulley
RPM1 = rpm of drive pulley
D2 = diameter of driven pulley
RPM2 = rpm of driven pulley

RPM2 = RPM1 x (D1/D2)

If your drive pulley is 12" dia and 1750 rpm and your driven pulley is 24" dia, then your driven speed is 1750 x (12/24) = 1750 x 1/2 = 875 rpm

Rod

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Butch(OH)

12-31-2004 19:21:29

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Re: Pulley/Gearing ratios??? in reply to Rod (NH), 12-31-2004 19:14:50

Sry Rod, you posted that while I wus typen.

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MPK

12-31-2004 23:07:24

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Re: Pulley/Gearing ratios??? in reply to Butch(OH), 12-31-2004 19:21:29

I know a simple way to figure shaft speed. I have done a lot of this through the years. Take motor shaft speed, multiply x motor pulley diameter, divide this by driven pulley diameter, this gives you driven shaft speed. Example, 1750 rpm motor x 6 inch pulley, divided by 24 inch compressor pulley gives you about 437 rpm. This will be close, your pulleys can be a little bit off.

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