Determining CFMs on an old compressor

rockyridgefarm

Well-known Member
Hey all,

Alls I got on the farm right now is a leaking old 10 gallon Montgomery ward 2 cylinder compressor. It works ok, but it sure take a long time to air up an 18.4-38 and forget about using an air impact or blowing off even a small piece of equipment.

Guys got a 60 gallon (he thinks) air compressor that's set to run on 240 for sale on CL. He says it takes four minutes from empty to 125 psi. I'm looking for a decent compressor to run an impact wrench, air up tires, and such. He wants $300. Should I bite?

Gonna go look at it tomorrow.

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You had better buy it, won't find anything any cheaper. That compressor will do the job for you. Just my thoughts, Keith
 
After you get it home , make a new outlet tube from the head to the tank , that one's kinked and is restricting the flow. Might be just as cheap to put on one from a truck air brake system....
 
When he said 240 did he say single or 3 phase? I have a 60 gal upright, this one looks more like 80 gal to me. If possible, listen to it run from zero pressure up. Some of those old compressors knock pretty hard when there is no load on them.

That sounds like a deal at $300 IF it is single phase. It should do all you want plus some.
 
Thanks for all the input so far.

Yeah, it is single phase. I looked into getting three phase run here. It'd take me 500 years to justify the cost AND I'd have to run a dozen phase converters or buy dozens of motors (15 just to run my feeding system, 12 exhaust fans, etc, etc)

So it's safe to assume this will be a better buy versus a 60 gallon upright Campbell Hausfield that's on sale for $650 at my local hardware store?
 
(quoted from post at 12:31:18 03/15/13) Thanks for all the input so far.

So it's safe to assume this will be a better buy versus a 60 gallon upright Campbell Hausfield that's on sale for $650 at my local hardware store?
Looks like it was desighned to be repaired if needed whereas many modern ones are throw away when tired.
Just my opinion,set the cut off psi as low as will serve your needs. Wear on motor and compressor increase dramaticly as psi increases. Granted,high pressure will inflate tires faster but a locking chuck while help with that,otherwise no sense keeping higher pressure than needed.
 
look for a tag on it that gives the cfm @ psi. if not find the maker and google it to find the specs on it.
 
(quoted from post at 09:19:58 03/15/13) Hey all,

Alls I got on the farm right now is a leaking old 10 gallon Montgomery ward 2 cylinder compressor. It works ok, but it sure take a long time to air up an 18.4-38 and forget about using an air impact or blowing off even a small piece of equipment.

Guys got a 60 gallon (he thinks) air compressor that's set to run on 240 for sale on CL. He says it takes four minutes from empty to 125 psi. I'm looking for a decent compressor to run an impact wrench, air up tires, and such. He wants $300. Should I bite?

Pictures are decieving but it looks smaller than 60. Take this formula with you though, you will need it anyway to get an accurate cfm rating.

1 gallon is 231 cubic inches.
The volume of a cylinder is given by volume = 3.1415 times radius squared times height. With that you can have a pretty accurate measurment of the tank size in gallons. Or, if you have a phone with you that has internet access, you can just punch in the numbers here: http://aqua.ucdavis.edu/calculations/Volume_of_a_Cylindrical_Tank.htm

Now that you have tank size, and given that you were told the time it takes to go from 0psi to 125psi, you can figure out the CFM of the compressor. Here is the link to that: http://mcguireaircompressors.wordpr...nd-out-how-many-cfm-your-compressor-delivers/

When I punched in your numbers, it came out to 9.57 CFM. Keep in mind that CFM changes depending on pressure. The only way to find out at the pressure you want is to do the calculations near the pressure you want. Check from 30-50 if you want the 40psi CFM rating or check from 80-100 if you want the 90psi CFM rating. If you are going to check it before you buy it, it wouldnt hurt to take a known accurate gauge with you that can be plugged in to the line.

I just went through this math stuff a little while ago when I bought a used compressor that was made in the lying years for ratings. Now with the new ones I think they still lie but with the HP ratings, not the CFM as much.

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(quoted from post at 22:02:27 03/15/13) Volume of cyl is 3.14 rsq x length [same thing as height]. pi r sq x ht
You forgot the PI

Thanks for catching that, I copy pasted and the website I grabbed it from didnt allow the pi sign.
 

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