I know this sounds completely stupid. I got this old compressor and the pump is no good - no compression. However, the Dayton 2hp 220v motor fires right up and runs strong. Will it drive a 5hp pump or do I need to drop down to a 3hp pump?
[OP]
Member
I know this sounds completely stupid. I got this old compressor and the pump is no good - no compression. However, the Dayton 2hp 220v motor fires right up and runs strong. Will it drive a 5hp pump or do I need to drop down to a 3hp pump?
Contributor
The motor can do 2 HP of work.
If you have a compressor that needs a 5HP motor you can only run the compressor at 2/5 rated speed with a 2HP motor.
I have no idea if the lubrication system will work at that speed............Rod.
[OP]
Member
ahh geez. What a drag. Thanks for the info though.
Member
Mike
In the quality compressor world. Companies like Quincy, champion, Jenny etc.. The will use the same pump for a 2hp, 3hp and 5hp compressor .. The pump will turn 450 RPM say at 2hp .. 620 RPM at 3HP and maybe 870 RPM at 5hp ..
The 2hp model simply uses a different sheave on the motor than the 3 and the 5 ..
The 2hp model will run so slow, that the pump will run forever without wearing out, and it will be significantly quieter. The number one enemy to a compressor pump is heat. Slower turning pumps run cooler ..
Really good quality compressors will put out say 15 CFM at 700 - 800 RPM.. A cheaper one will use a smaller pump, and turn it 1200 RPM.. The output is the same, but the lifespan of the two machines is not even close.
Go for it .. Just get the right sheave ..
Contributor
Dayton = Grainger. Look up pump, and they most likely will have a chart showing what motors and sheaves to use. The pump can be rebuilt, unless it was run dry (no oil.) Then it's usually toast. What doesn't pump do? Stuck /frozen, low out put leaks oil etc?
Contributor
I built a compressor at my last shop and ran a large pump at half speed on purpose. It was on a bigger scale but the same idea. The larger pump at half speed is still putting out as much air as a 1/2 size pump running twice as fast, but the pump is running cooler, the air is cooler and it will last longer.
That compressor ran my shop and a connected auto repair shop for 13 years and was still going when I sold the building.
[OP]
Member
Well, the motor comes on and turns strong but the compressor pump just freewheels like there's nothing inside so I guess it has no compression. At any rate, it's an old compressor pump and I doubt if it puts out any serious cfm although I wouldn't know for sure. I don't want to get it fixed unless it's going to put out. I've snapped a couple of pics for reference.
IMG_0998.jpgIMG_0999.jpg
So, since the 2hp motor seems like it's worth saving, I was just going to slap http://www.harborfreight.com/5-hp-14...ump-60754.html on there. This pump claims 17cfm @ 40psi. I would imagine that's on the optimistic side but I think it would, in reality, produce PLENTY of air for spraying finishes.
But, then I read the comment about running it at 2/5 the power, and that would not be enough air at all then right? If the motor runs the pump at 2/5 the power, then I get 2/5 the air correct? Is it a linear relationship?
But, then Rick Fisher suggested getting a new "sheave" which I had never heard of before. So, from my reading, that's just another term for "pulley". So, then are we talking about putting a larger diameter pulley on this motor and we get more RPM to the pump?
Why is the motor even rated in HP then?
so confused- sometimes, you just feel plain dumb.
Contributor
You need a smaller pulley on the motor to run the compressor at a lower speed.
It's not practical to change the compressor pulley as it has the cooling fan built into it..........Rod.
[OP]
Member
But I would need a larger pulley on the motor to run the new 5hp compressor pump faster. No?
Member
Mike the 2hp motor will not have the power to run the compressor at the same speed as a 5hp motor, but by putting a smaller pulley on the 2 hp motor you will turn the compressor at a slower speed which the 2hp motor can be capable of doing. What will change is the time it will take to fill the air tank and shut the compressor off.
[OP]
Member
What about cfm? I guess what I'm saying is that I need this guy to pump so I can run my HVLP sprayer without it getting out of breath. Does running the pump slower reduce cfm output then? Sorry. I'm just not getting it.
Contributor
Not an air compressor expert by any means but I wonder if it'd be worth checking the valves in the head of the compressor. If the pump 'freewheels', I wonder if one valve is broken or stuck open so the cylinder is never sealed and therefore can't build pressure. I try to look at the simple/cheap stuff first though I'm not always successful. If your compressor is indeed not fixable, Harbor Freight also sells a 3 h.p. compressor pump. You shouldn't have to slow that one down as much.
http://www.harborfreight.com/catalog...ompressor+pump
[OP]
Member
*duplicate* - darn browser cache.
Last edited by Mike Dowell; 01-22-2015 at 10:11 AM.
Member
Yes, CFM output from the pump will be approximately proportional to rpm. The tank is between the pump and your tool, so the effect of the lower rpm will depend on the size of the tank and the pattern of draw of the tool. A sprayer is a mostly steady draw, so it will most likely pull the tank down to the outlet pressure, at which point you will only get what the pump is supplying at the input.Originally Posted by Mike Dowell
[OP]
Member
've also got this old girl too.but it looks even smaller and has a bad 1hp motor. This one I identified the compressor pump as a Speedaire 1z944 but I can't find the specs on it. My father-in-law suggests using this compressor pump(presumed good) along with the 2hp motor from the other one. But, this pump just doesn't look like it puts out. I (obviously) know very little about compressors but he swears this will put out plenty of air. However, 30 years ago, we didn't use HVLP either. My sprayer calls for 12 SCFM @ 45psi.
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