Compressor Help

[bpankratz]

Hi guys, I'm trying to build a temporary air compressor to pull the through until I find a Quincy or Kellogg pump to suit me. I have the pump off of this old Craftsman air compressor. It's a small 2 cylinder single stage pump.

I also have a Baldor 1hp motor that spins 1750 RPM

I need to know a few things, what pully sizes should I use to get the maximum rpm this pump can run? (I assume this is 1010 RPM?) Also can I put a higher (maybe 160 psi?) pressure switch in, and will the pump reach this PSI?

Longevity is not an issue. All components were free, and will be replaced as soon as I can find a decent pump. I have a 7.5hp Baldor motor waiting.

Thank you compressor gurus!

 

[sberry]

No, there is a practical limit to the pressure.

 

[matt_i]

I think you are limited by the starting torque of the electric motor.

Most compressors I see are a 1:3-ish underdrive on a 3450 rpm motor. So your thought of a 1:2-ish underdrive on a 1725 rpm motor are "in the ballpark".

There is no way a single stage is going to reach 160psi unless its a purpose-built small unit. Count on 90psi.

 

[chew]

I'll add it's a 5hp rating on the head at 1010 rpm. So to pair it to a 1hp motor you will need to run the compressor at 202 rpm to put a 1hp load on the motor. Your other option is to just use the 7.5hp motor driving the compressor at 1010 rpm.

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[bpankratz]

I think you are limited by the starting torque of the electric motor.

Most compressors I see are a 1:3-ish underdrive on a 3450 rpm motor. So your thought of a 1:2-ish underdrive on a 1725 rpm motor are "in the ballpark".

There is no way a single stage is going to reach 160psi unless its a purpose-built small unit. Count on 90psi.

Ok, so maybe for now I will stick with a lower pressure switc, and try to run the motor and pump in the 2:1 - 3:1 area.

 

[bpankratz]

I'll add it's a 5hp rating on the head at 1010 rpm. So to pair it to a 1hp motor you will need to run the compressor at 202 rpm to put a 1hp load on the motor. Your other option is to just use the 7.5hp motor driving the compressor at 1010 rpm.

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This doesn't add up to me. By this you are saying I need to run about a 1:7 ratio, right? The 2 pullies I have from the original motor are about 10" and 3". However I dont know the specs on the original motor. That being said I can't see it being more powerful than the motor I have now.

I could absolutely use the 7.5hp motor now, I just thought this would be easier for the time being as I can probably run the 1hp motor without using a magnetic switch box.

 

[chew]

This doesn't add up to me. By this you are saying I need to run about a 1:7 ratio, right? The 2 pullies I have from the original motor are about 10" and 3". However I dont know the specs on the original motor. That being said I can't see it being more powerful than the motor I have now.



I could absolutely use the 7.5hp motor now, I just thought this would be easier for the time being as I can probably run the 1hp motor without using a magnetic switch box.

My guess is the original motor was a 3hp at 1725 rpm. 10" and 3" pully = 3.33:1 is 518rpm at the compressor. 5hp rated compressor at 1010rpm. 518/1010=0.51 take that 0.51x5hp=2.6hp load running at 518rpm on that compressor. (perhaps that pully is 3.5"?) If you want to run a 1hp load and you motor is 1725rpm you need about 8.5:1 reduction. 17:1 if the motor is 3450rpm.

All that being said I've never underdriven a compressor that much before. The motor might be able to run a bit more rpm at the compressor. My experience comes from sizing motors to hydraulic pumps. There are also effency losses to account for but they tend to equal the service factor of 1.15 of the motor on sub 10hp loads.

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[bpankratz]

My guess is the original motor was a 3hp at 1725 rpm. 10" and 3" pully = 3.33:1 is 518rpm at the compressor. 5hp rated compressor at 1010rpm. 518/1010=0.51 take that 0.51x5hp=2.6hp load running at 518rpm on that compressor. (perhaps that pully is 3.5"?) If you want to run a 1hp load and you motor is 1725rpm you need about 8.5:1 reduction. 17:1 if the motor is 3450rpm.

All that being said I've never underdriven a compressor that much before. The motor might be able to run a bit more rpm at the compressor. My experience comes from sizing motors to hydraulic pumps. There are also effency losses to account for but they tend to equal the service factor of 1.15 of the motor on sub 10hp loads.

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Thank you for the thorough explanation. This stuff is way over my head haha. I will work off of what you gave me and try something! Hopefully I'm not too wrong haha!

 

[chew]

Let me know how it works out and what you end up trying.

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[bpankratz]

Let me know how it works out and what you end up trying.

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I absolutely will. Might be a while as I need to wire my garage as well. Haha.

 

[CGT80]

That isn't a 5hp motor bit rather about 3hp. The 1hp baldor may not be enough. Those pumps are junk and had a hard enough time reaching 130psi. I wouldn't spin the pump any faster than 1010 rpm, if that is the nameplate that went with that pump. The 7.5 baldor would be fine with the right pulleys and wouldn't pull max amperage with such a small load. I have a few of those cman pumps and had a similar sanborn pump break a rod. A real 5hp motor pulls 24 to 28.8 amps at 240v. That pump is better than nothing but not built very well compared to what you are looking for. I wouldn't push it too hard if you want it to last a little while.

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[rburke65]

I bought a Champion 5hp., 60 gal. tank, 2 stage, from TP Tool. 805 rpm....quite. Expensive....inexpensive....depends on you but I’m happy I bought it.