Determining Compressor CFM output

[justified07]

New guy here!

I was helping someone could help me. I have a brand new compressor pump that I would like to mount on a tank. It is a single stage, twin cylinder, and the specs on the website say it is a 1 to 1-1/2 HP, 6.6 CFM displacement CFM, 4 CFM delivery CFM, 140 max psi.

Can someone help me understand what CFM output I would be looking at if I mounted this on a 60 gallon tank?

Does the 4 CFM delivery mean that it would only deliver 4 CFM at say 125 psi?
That seems low considering it is a twin cylinder.

I looked up what I could online, but I didn't see anything to tell someone how to choose a pumo, motor, and tank size for desired delivery.

Thanks in advance!

 

[SGKent]

Think like a bathtub and faucet as an analogy - if you have more water going out the drain than water coming in thru the faucet the bathtub will drain. The compressor CFM has nothing to do with the tank. It is what CFM the compressor will provide - like the faucet in the bathtub analogy. Let's say you added a 60 gallon tank - that is like a bigger bathtub than say a 20 gallon tank. Once that air tank reaches working pressure, as you use up air going out, the compressor will replace the air by sending new air into the tank. Let's say you take 15 CFM out of the tank but only put 4 CFM back into the tank. The tank will drain in a couple minutes and 4 CFM will be your flow. Unless you are doing jobs that are a minute or two in length, 4 CFM is the most you will get out of your arrangement. And, you'll be working at 20 or 30 PSI when that tank gets drained. 4 CFM at 20-30 PSI won't do much. I have two twin cylinder compressors in parallel, each providing 9 CFM at 125 PSI. That is barely marginal to paint, glass bead blast, etc.. I have used one to blast and paint, and I would be able to work 5 minutes then wait 5 minutes for the tank to fill. I had to keep fans on the compressor all the time to keep it cool because compressors are not meant to work at a 100% duty cycle. That is why I added a 2nd one. Many folks here just buy one big compressor for that reason.

 

[ard]

the specs on the website say

Post a link to that website.

 

[justified07]

Think like a bathtub and faucet as an analogy - if you have more water going out the drain than water coming in thru the faucet the bathtub will drain. The compressor CFM has nothing to do with the tank. It is what CFM the compressor will provide - like the faucet in the bathtub analogy. Let's say you added a 60 gallon tank - that is like a bigger bathtub than say a 20 gallon tank. Once that air tank reaches working pressure, as you use up air going out, the compressor will replace the air by sending new air into the tank. Let's say you take 15 CFM out of the tank but only put 4 CFM back into the tank. The tank will drain in a couple minutes and 4 CFM will be your flow. Unless you are doing jobs that are a minute or two in length, 4 CFM is the most you will get out of your arrangement. And, you'll be working at 20 or 30 PSI when that tank gets drained. 4 CFM at 20-30 PSI won't do much. I have two twin cylinder compressors in parallel, each providing 9 CFM at 125 PSI. That is barely marginal to paint, glass bead blast, etc.. I have used one to blast and paint, and I would be able to work 5 minutes then wait 5 minutes for the tank to fill. I had to keep fans on the compressor all the time to keep it cool because compressors are not meant to work at a 100% duty cycle. That is why I added a 2nd one. Many folks here just buy one big compressor for that reason.

Thanks! Makes perfect sense to me. Can you tell me how you run compressors in parallel? Do they both feed a common tank? Do they both still shut off by their own pressure switches, or do you have them share a switch off of a common tank?

 

[justified07]

Post a link to that website.

I have a PK40, which is no longer made. I split the specs. between the PK20 and PK50 models. They can be found on Pumaairusa, under products, single stage, belt drive, oil lube pumps.

I don't have enough posts to post links yet it says.

 

[Showkey]

AVE went a pretty good rant on the CFM a deceptive rating system. Even after the class actions it’s still deceptive. Video has an explanation and testing results.

 

[bochnak]

Rule of thumb is 2-3 CFM per HP. So for your pump, the 4cfm is probably rated at 90psi.

I did a video on cfm calc here:

Also, consider that you can buy a brand new 6cfm compressor for $329. You are going to probably spend that on pulleys, belts, motor, etc. to cobble something together and have less cfm.

Matt

 

[sberry]

Its pretty dinky for all the effort.

 

[56Mark]

I would only use it if I could find a cheap deal on CL where someone had a pump die and the tank, motor, switch, etc is in good shape. One HP will probably get 2 1/2 CFM and 1.5 HP 4 CFM. It would be fine for nail guns, pumping up tires, some small air tools, etc. Not enough for DA sanders and other large air sanders, HVLP guns, and blasting.