Compressor tank pressure margins Craftsman (Devilbiss)
I have a Craftsman (Devilbiss) single stage oil-free compressor, about 12 years old. It has an ASME rated tank and has a Furnas pressure switch that is labeled 100/125.
I believe the unit is advertised as a “125psi compressor.”
The problem is that the unit has never cut in until the tank pressure drops to 90psi. That difference between 90 and 100 is just enough to cause performance problems with some of the tools I’d like to use.
I’ve tried adjusting the (single) screw on the pressure switch up, but even a very slight adjustment results in the cutoff pressure raising up well above 125psi. I’d install a different switch if I could find one that truly had a 100psi cut-in pressure, but I can’t.
So that leaves the question, would this tank be safe to run at pressures up to 150psi so that I can be confident about increasing the adjustment on the existing switch? Is there really a difference between a 125psi tank and a 150psi tank (which seems to have become more commonplace in the last few years)?
Thanks for any advice!
Typical pressure switch adjustments are in the 1/4 turn range. Sounds like you may be adjusting the nut too much?
On the tank that ASME plate should indicate the safe pressure of that tank. If no such plate, go with the compressor manufacturers limits.
What I suggest you do is put the term “how to adjust pressure switch” into your search box for guidance. There are many pressure switches on the market that allow you to adjust both cut in and cut out.
Mind you, reducing the range between cut in and cut out means your compressor will cycle more often, with frequency of maintenance and life expectancy of the air compressor being affected.
Update by: Mike
After I posted the question I pulled the compressor out from the wall where I could get a better look at it.
There was indeed a metal plate tack welded to the tank, indicating it was certified for 150psi at both high and low temperatures.
Even better news is that I apparently bought an exact replacement pressure switch around the same time I bought the compressor, so I went ahead and installed it. Whereas the original switch seemed very difficult to adjust properly, I was able to adjust the new one easily with about 3/8 of a turn, so that it now cuts in at exactly 100 and cuts out at about 134.
Now I just need to figure out why it seems to lose about 1psi of pressure per minute (and did with the old switch too), but at least now I know it’s not the switch. Hopefully it’s just the tank drain or a loose fitting, and not the check valve. Thanks again.
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