Pressure drop is just what it says. For example, there is 120 PSI coming out of a compressor discharge, yet at the application half a plant away, the pressure is 95 PSI. How come?

As air travels through the air lines, the friction of the air moving along on the inner wall of the air line slows the air at the outside of the air stream, and the air in the middle moves faster as a result. This creates turbulence. Turbulence contributes to pressure drop.

Then, every fitting, every orifice the air travels through, every leak point the air travels past, slows the travel of the air and reduces the pressure that can be delivered. If air is moving more slowly, it takes longer to come up to pressure at a specific location.

Miniature barbed fittings for poly tubing.

Every fitting, every orifice, every air line all contribute to pressure drop in compressed air flow.

If the air-using application is using air faster than it can arrive at the point of use, the results of pressure drop is that the application will starve for compressed air negatively affecting the work performed.

Too Big An Air Line?

Obvious scenarios that will cause significant pressure drop are having the air supply line at 3/8″ pipe size, and the application requiring 1/2″ lines. As air exits the 3/8″ line to the 1/2″ port, it expands, and the pressure drops.

As air moves from the compressor receiver or discharge through the plant mains, typically the air lines reduce in size, this helping ensure that the air pressure that gets to the application is sufficient as long as the line size provides sufficient flow for the application.

Eliminate the Leaks!

Eliminate compressed air leaks and remove choke points between the source and end use of your compressed air. Where possible plumb air to reduce elbow use, to help reduce pressure loss through air turbulence.

In a system that is designed and built correctly, between the compressor discharge and point of use, the norm is to see a 5-10 PSI drop. If you are seeing more pressure drop in your air lines than that, there is likely some problem with your compressed air plumbing.

I’m happy to provide this link to an article in Fluid Power World also addressing this issue, but rather than pipes, it’s pressure drop through fittings. While the article focuses on hydraulic fittings, I expect the theory applies to any fluid, including compressed air. .