Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2005

Pressure Differential (Pressure Drop) in Paint Hose

Q. I need help in determining my actual PSI when using shop air spray nozzles. OSHA regs state that shop air used for cleaning purposes be regulated at 30 PSI or lower. I have my regulator set to 30 but the actual pressure at the nozzle seems quite low. I am using 1/4" piping at the regulator and then reducing that down to 1/8" tubing (8ft long) for my spray nozzle. Does the reduction in inner diameter effect the PSI at the point of use or is it only effecting air flow?

A. I'm not sure if you are referring to an air or fluid hose, but here is my answer in case you are referring to an air atomizing hose. The principle is the same if you are using a fluid hose, but the hose diameter would be different.

By throttling down the amount of air that can pass through the air atomizing hose, you are loosing all your air pressure. You need to do exactly the opposite. Remove all unnecessary Quick Disconnect fittings, and for those that you absolutely need, use 3/8" diameter. Replace the 1/4" air hose with a 3/8" air hose.

If you are using a hose to carry fluid, such as solvent, the same principle applies. Keep the hose as large as possible and remove unnecessary restrictions.

Best wishes,

Ron Joseph