Talk to me about air compressors...please

[SemiSweet]

(12-19-2020 )Precisionw900 Wrote:  Not to hijack the thread but is it common for ISX compressors to have a knock sound to them? I have heard 3 of them including mine that have a knock or rattle sound at idle when pressure is high. Mine will stop when air drier pops off then knock builds as pressure builds? Common or compressor problems ahead?

Check for air pressure between your compressor unloader port and governor when the compressor is pumping. Mine would rattlesnake when getting close to pressure cut out and quit once the compressor unloaded and the dryer purged. The governor was passing at higher pressures causing the air dryer purge valve to pop and sputter. Replaced the governor and good to go. I have also heard of this happening if cutout pressure is set to high to begin with. Simply adjusting the governor to a slightly lower cut out pressure solved the problem.

A Carboned up compressor head could cause a similar sound when unloader valves are sticking or not reacting as quick as they should. Cummins has a cleaning procedure on quickserve but a quick and dirty way is to pull the inlet tube and discharge line and let it suck a little wd40 or seafoam through the inlet while the compressor is loaded to lube and clean the internals.