Air Compressor and Air Dryer Air Supply Problem

air compressor and air dryer
(Last Updated On: August 3, 2020)

I have a 5 hp compressor very much capable to run a device that I have been running.

3/4″ black pipe out ( in a climate controled room of 70dg).

My supplier sized my air dryer @ 15cfm with 3/8 od copper or (1/4″ id copper) in and out of the air dryer.

The device will not operate properly with the air dryer in the system.  I can bypass the air dryer and the device works properly.  I have this problem on 2 of the same compressors and air dryers.

My question is,  is the 3/8″ OD copper lines in and out of the air dryer constricting my cfm at the end of my run to much?


We answer…

Rule of thumb says your 5 HP compressor should give you about 20 CFM of air at 90 PSI.

If, before the dryer was installed, that 20 CFM gave you sufficient air flow and pressure to run your device, and then adding a dryer in the middle stopped your device from working properly, then yes, that’s the problem.

Are you able to run your device with a 1/4″ tube? Tee off the 3/4″ pipe with a 1/4 poly tube, bypass the dryer, and see if your device runs. If not, then you don’t have enough air coming through a 1/4″ line.

Remember that you will have pressure drop through any line, and the pressure loss through the 1/4″ tube might be the problem, not the dryer.

Next question: What’s the CFM requirement of your device? Then, compare that to the dryer capacity. The air dryer will have a flow rating based on a certain CVFM at a specific PSI. Make sure that the dryer is rated for sufficient flow for your device.

Can you plumb a larger hose from the 3/4″ pipe top the dryer? As you know, I’m sure, hose is measured on the I.D., so buy some 1/2″ or even 3/4″ hose to run to the dryer, and then to your tool.

So, make sure the dryer can handle the flow the application requires, and if so, open up the lines.

Also, if you have any other appliances using the same air supply, you must account for their consumption in the dryer capacity. If you have two tools on the same air line, then you will, eventually, have them both running at the same time.

One other thing. If the tool use is intermittent, then perhaps you need a large reservoir of compressed and dried air after the dryer, from which the tool can pull air. That might help.

Hello, I am Bill, the Compressed-Air-Man. I have years of experience in industrial and residential compressed air applications, air compressors and general pneumatics. I created this site to help professionals, students, and DIYers understand and properly implement and maintain compress3ed air systems.


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