Thread: What PSI to set the cutoff on an old Comp?

OK, so a friend bought himself an old compressor. IMHO it was a bargain. A bit exxy to bring up to scratch, but it's now a goer.

The original cutoff was the very, very old school type, which ran up to a preset amount (in this case 75PSI, although the cutoff case is stamped 100! ) and then opened the dump valve until it dropped back to the cut-in pressure again. (50PSI, although the cut-off case is marked at 80.)

So, not only was the cutoff performing below spec (no adjustments possible!) when in use the motor was constantly cycling every minute or two. Not acceptable. To bring it up to par I replaced the old cutoff with a new 4-way job and installed a 150PSI safety relief. (With the added bonus that it now has an on/off switch!)

Anyways, the new cutoff system is adjustable... and I was wondering what people would recommend as the max PSI. The old unit was cycling up to 75, but that's the very bottom end of the new cutoff. (Actually, to get it down to 75 the adjustment screw was just beginning to work "loose." ) And I know there are tools which need a bit higher pressure that that to run properly.

On a preliminary run, just to check my wiring, I let it run up to 100PSI before I decided to hit the panic button. Not that 100PSI is that much, but this is an old and untested cylinder. We know it handles 75PSI alright, but everything beyond that increases the risk of going BOOM at an exponential rate, y'know?

Once it was all assembled to my satisfaction, I guesstimated a safe setting and preset the cutoff to 90PSI as a compromise between cylinder safety and the higher PSI tool requirements.

What do you think? Where would you set the upper cutoff? And why?


(I'd post relevant links but it's not mine and I wouldn't feel comfortable without the permissions of all involved. But I still wanna know your thoughts as to my guesstimate... 'cos it's all a bit "iffy," y'know? I'm sorta wondering if I should've stuck with as close to 75PSI as I could adjust it, even though that was close to "disassembling" the unit!? )