- Question Title: 375 Sullair JD diesel compressor problem
- Asked by: Guest
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- Answers: 1
Dear Sir.
We have a 375 Sullair JD diesel powered air compressor with slightly over 9000 hrs on meter, which for a diesel engine in this application is a lot of hours.
We have noticed with our air receiver guage that in previous months, we could maintain approx 110-125 psi and blast continuously using a # 6 nozzle. Now the compressor is only maintaining 85 psi under similar circumstances. I originally thought the air end might be the issue, but if the life of the air end is approx. 40-100k hours, then perhaps the problem is in the diesel getting "tired" and not the airend.
Just wanted your thoughts on this issue. We have not experienced any excessive oil in the air line, which might indicate a problem, so I feel the air/oil seperator is OK.
A new compressor is in the 38-48K price range. Perhaps a rebuild of the engine is a starting point and a more cost effective move. Any suggestions from you would be greatly appreciated. Thank you for your time.
Answers & Replies
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Hi Marty,
Thanks for your question and sorry for my late reply.
To find out which part is the problem, the air end or the diesel engine.. best is to check the diesel engine speed (RPM). For this you need a rpm meter. Run the compressor at full load and full pressure and check the rpm. Compare it to the value in the manual (i'm sorry i don't have it).
If the diesel engine is able to reach full RPM at full pressure, than there is nothing wrong with the diesel engine.
Be sure to check this at full load and maximum pressure. To do this, open the discharge valve slowly more and more.. until the engine reaches highest rpm. Don't open the discharge valve too much, or the pressure will drop back (making it easier again for the engine).
The control system in such compressors usually control two thins: the inlet valve (open-close) and the engine rpm. If the engine cannot reach full rpm, it could also be a control issue.
I found a picture online of this compressor (see above). You can clearly see the engine speed control piston in the left. Check if this is making a complete stroke (to full rpm setting), otherwise, see if you can 'help' it by hand and see if ti revs up some more.
Air ends have a typical lifespan of around 40.000 hours, But this is for stationary compressors. Expect a lot less for portable compressors..
Good luck and let me know if you need more info or it this was helpful.