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Old 08-03-2010, 03:55 PM
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Sorry...another air compressor question...

Hello one and all...been lurking for a while now and thought I would just take the time and join and post....lol.

My question is that I have an old CH VT5587 that needs a pump...the motor and tank are fine...but it needs a pump.

Is it possible to put a 5HP 2 stage on the tank? It has a twin pump single stage and a 5 HP motor....

Has anyone done anything like this before?

Thanks in advance for any and all help with this...

Bill

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Old 08-03-2010, 04:23 PM
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Sure you can but are you sure that is actually a 5 HP motor? Look at the data plate on the motor and see what the AMP rating is at 240 volts, if it is the very common 15 AMP motor it is only 3 HP and you would need to find a pump compatible with that motor. CH was notorious about exaggerating, just out and out lying actually, about the motor HP but that data plate is mandated by law and they had to be truthful on it.
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Old 08-03-2010, 04:26 PM
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Oh...yeah, I'll check...did not realize that...THANKS....
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Old 08-03-2010, 04:30 PM
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Ok...its a Century brand motor....with 230 @ 15 amps?????

Thanks again....
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Old 08-03-2010, 04:32 PM
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Ahhhhh....ok, so (duhh) I reread your post there, and I see that the motor is a cheapo....LOL! So.......I cant really do that then, right? LOL!
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Old 08-03-2010, 08:02 PM
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The Century is not necessarily a bad motor as far as econo type motors go and if it is good along with the other components then replacing the pump is a viable option vs buying a new compressor. A small two stage pump would certainly be a very good choice if you could find one cheap enough but if not then a single stage is not a bad choice either. You might check with Surplus Center as they carry a lot of compressor pumps and although most of them are expensive industrial types they often have some smaller more economical units. In this case you will need to look for something in the 3 HP range.



www.surpluscenter.com
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Old 09-09-2010, 07:31 PM
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15 amps is as stated, 3 hp.. So just find a pump for a 3hp motor and you're golden! Doesn't matter if it's 2 stage or single stage. Just look at the rpm specs of the motor and adjust pulleys accordingly.
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Old 10-24-2010, 12:11 PM
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Couldn't you just turn a larger compressor head slower? Like in his case, use a 5-6hp compressor head and turn it at roughly half speed (smaller motor pulley or bigger compressor pulley, or even a jack shaft...)
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Old 10-25-2010, 11:07 AM
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You can run a larger pump slower by changing pulleys but only within it's design limits since if you drop below minimum speed you could run into oiling problems plus if you run too slow efficiency can also suffer. Running a large pump at slow speed is a good idea and a lot of the larger outfits do this but unless you fully understand exactly how to balance the RPM, CFM and oiling issues you could end up with poor performance or a burned out pump from lack of lube. Generally it should be safe enough to run a 5 HP pump design with 3 HP by slowing it down UNLESS it is already rated for 5 HP at a slow speed. The way to do this is to change the ratio by about 30% to start (assuming 3 HP and a 5 HP design pump) then use an AMP meter to determine the power draw of the motor during start and run, adjust the ratio with different pulleys until the motor is near it's max rating at start and run/shut off but DO NOT exceed either rating!
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Old 11-04-2010, 07:40 PM
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Oldred, do you have any idea how to figure that speed out (the minimum speed that a pump can be run at)?

I have a big old kellogg compressor head that I want to run like that, probably want to run it at max with a 5hp/220Vmotor but can't seem to find enough info about what speed it was run at originally or with how big a motor. I don't even know if it should turn clockwise or counterclockwise (or if that would be facing the front of the compressor or sitting from the compressor side).

I have a 15 or 18" pulley that I can make work with that compressor, so it should give me a little leeway for the motor pulley size.
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Old 11-19-2010, 08:37 PM
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A 5hp 2 stage compressor could probably be run at full speed with a 3hp motor, you just couldnt pump it up to 175 psi. Probably 120psi at most. They saylor beall 705 compressor is rated for 3hp and 5hp use although they do say it should run slower speed (and thus less CFM) but still run up to 175 psi.

I think it would recover quicker by spinning it at full speed and just not as high of pressure. Most applications dont need high pressure anyways.
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