Air compressor rpm advice needed.

[sld961]

I have an Emglo L pump and a 3hp 3450 motor. The pump has a 10"pulley. I was planning on getting a 2.75" pulley for the motor to get around 950 rpms at the pump.

Turns out that I can't find a 2.75" pulley with a 1.125"bore. The smallest one I can find is 3.05", which will put me at 1050rpm.

If I read the table right, I'll only be able to get about 50psi with a 3hp motor at 1050rpm. Am I reading that right?

 

[shoot summ]

You aren't reading the table right.

That column doesn't say "max pressure".

Its the cfm at that pressure/rpm the way I read it.

 

[Boilerhouse]

Pulley size will not affect psi. Will affect cfm.

 

[Roberts210]

Ditto what the above two guys say.

 

[redmondjp]

You aren't reading the table right.

That column doesn't say "max pressure".

Its the cfm at that pressure/rpm the way I read it.

But it essentially is the maximum pressure, for that given motor HP and pump speed. That chart shows you what you can get with a 3HP motor.

And unfortunately, if you try to pump higher than approximately 75psi, given the OP's pulley with a pump speed of 1050RPM, you will be overloading the motor (and it may not start at 75psi, even with an unloader).

You would need a 5HP motor to run at that speed and get any usable pressure. So smaller motor pulley, or bigger motor.

And pulley size doesn't affect the pressure, but it does affect the horsepower needed to develop that pressure.

 

[larry_g]

X2 with Redmondxp. For a given HP you can have volume or pressure but not both.

So OP you are reading it correct given your speed and HP 75 psi is a good guess to max psi.

 

[sld961]

But it essentially is the maximum pressure, for that given motor HP and pump speed. That chart shows you what you can get with a 3HP motor.

And unfortunately, if you try to pump higher than approximately 75psi, given the OP's pulley with a pump speed of 1050RPM, you will be overloading the motor (and it may not start at 75psi, even with an unloader).

You would need a 5HP motor to run at that speed and get any usable pressure. So smaller motor pulley, or bigger motor.

And pulley size doesn't affect the pressure, but it does affect the horsepower needed to develop that pressure.

Thanks, this is what I was thinking. Now I have to find someone that makes a 2.75" pulley with a 1.125" bore, or find a different motor.

 

[FTG-05]

2.75" OD with 1 1/8" bore: http://www.surpluscenter.com/Pulley...Diameter:2.75&fq=ATR_Bore_Fractional:1\-1/8\"

 

[sld961]

2.75" OD with 1 1/8" bore: http://www.surpluscenter.com/Pulley...Diameter:2.75&fq=ATR_Bore_Fractional:1\-1/8\"

Thanks. But after running the numbers again, I need 2.55" if I want 150 psi. Plus I need double groove.

 

[md21722]

Why do you need a fixed bore sheave? You can go with a bushed sheave that may give you more options.

https://www.grainger.com/product/TB-WOOD-S-Quick-Detachable-Bushed-Bore-WP172267/_/N-hxd?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/5YKK7_AS01?$smthumb$#nav=%2Fproduct%2FTB-WOOD-S-Quick-Detachable-Bushed-Bore-WP172267%2F_%2FN-hxdZ1z0e2s5%3FR%3D5YKR5%26_%3D1455468832431%26picUrl%3D%252F%252Fstatic.grainger.com%252Frp%252Fs%252Fis%252Fimage%252FGrainger%252F5YKK7_AS01%253F%2524smthumb%2524%26s_pp%3Dfalse

https://www.grainger.com/product/TB-WOOD-S-QD-Bushing-5YLF9?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/5YLF7_AS01?$smthumb$

 

[sld961]

Why do you need a fixed bore sheave? You can go with a bushed sheave that may give you more options.

https://www.grainger.com/product/TB-WOOD-S-Quick-Detachable-Bushed-Bore-WP172267/_/N-hxd?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/5YKK7_AS01?$smthumb$#nav=%2Fproduct%2FTB-WOOD-S-Quick-Detachable-Bushed-Bore-WP172267%2F_%2FN-hxdZ1z0e2s5%3FR%3D5YKR5%26_%3D1455468832431%26picUrl%3D%252F%252Fstatic.grainger.com%252Frp%252Fs%252Fis%252Fimage%252FGrainger%252F5YKK7_AS01%253F%2524smthumb%2524%26s_pp%3Dfalse

https://www.grainger.com/product/TB-WOOD-S-QD-Bushing-5YLF9?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/5YLF7_AS01?$smthumb$

Thanks for the links. It looks like I could get as low as 2.65", but not 2.55". That may be an option if I can't find something in 2.55.

I'm going to call my local bearing and drive store to see what they have.

 

[redmondjp]

2.65" is close enough. You're pushing any single-stage compressor really hard to get it up to 150psi. You will be better off setting it to turn off at 125 - 130psi anyways. The 2.65" will get you there just fine.

 

[sld961]

Update. I found a fixed bore 2.50" od pulley with 1 1/8" bore. Got it test fitted on a piece of plywood and wired it into the breaker box for a test. Sounds good, but I only had one belt, so it slipped when it started building pressure. Should be good with 2 belts.



Then got it painted up.