Calibrate Pressure Switch?

Is it possible to calibrate the pressure switch? Ours seems to shut off closer to 105 psi. I would like to be able to carry the maximum capacity of air on board!

Sadly the pressure switches are factory set…there’s nothing you can adjust. Some will be low, some high.

Last year we tested 5 and used the one with the highest pressure. They are factory set. Best you can do is order a few more test them and cross your fingers.

You might try putting the pressure switch far away from the compressor, so it is less likely to see momentary peak pressures that are above the steady-state pressure. For example, it might help to put it on the other side of the storage tanks from the compressor, if you can do so…

You can adjust them. Not to be done lightly, but your robot inspector will check it during inspection. PM me for directions if you need them.

Frank, would you mind sharing how to adjust the switch? We’ve tried 4 switches and they are all shutting off around 106 PSI.

Pressure switches cannot be calibrated. They come as they are and not all are alike. Big Al posted somewhere that if it is cutting off early like that then it could be an old one that is starting to fail. Try moving farther from the compressor (still on 120PSI side) or a new switch.

Frank I believe that you are thinking of the pressure relief valve.

That’s what I thought too - as far as I knew the pressure switch is a sealed unit that doesn’t take kindly to being disassembled.

1 Like

Have you tried a different gage? If 4 switches are reading the same I would suspect the gage is bad.

Calibrating the pressure switch is possible. There is a setscrew on the side which is allen head, the manufacturer has originally set them and put silicone around the threads where the plastic meets metal base. That is what the set screw is for. Take a utility knife score the silicone and peal it out. Loosen setscrew pressurize system, adjust pressure switch by threading the top and bottom half in or out (A little adjustment goes a long way). Adjust to the proper cut in/out pressure, tighten setscrew, reverify pressures, re-silicone – done.

Does the steps to calibrate the pressure switch fall within R76? It doesn’t seem to so I’d be careful about actually doing this.

The precedent might be that you can adjust the emergency relief valve (and often must) despite it not being an exemption in R76. Then again, the relief valve is governed by R87, which includes a blue box text that explicitly allows for adjusting it. R88, which governs the switch, does not have any similar language. It’s sort of a grey area.

My gut would say it’s not a alteration of the pneumatic part per se, but a calibration of one using a method designed for that purpose. So long as it turns off the compressor at or below 120 and does so consistently I don’t see a rules compliance issue. This hinges on whether the GDC/Inspectors interpret it as a alteration or not.

It’s probably worth a Q&A.

I did a quick look and nothing states that you have to use the Nason pressure switch either (correct me if I’m wrong). Apparently the nason pressure switch may be ordered in a 120PSI variety as well.

We are specifically allowed to use other switches; see Q258. Also see http://www.chiefdelphi.com/forums/showpost.php?p=1348274&postcount=9

Yep, we tried multiple different pressure gages and they are read similarly (within a psi or two).

I do this too for the Nason SM model but apparently the SM model is not marketed as field adjustable. Only the CJ model is marketed as field adjustable.
http://www.nasonptc.com/pdfs/Switches_Catalog.pdf

I could not find a source indicating the SM model is ok for field adjustments. As far as I can tell, the manufacture never intended for the SM model to be adjusted by the user.

So would this be an illegal modification to a pneumatic component? Luckily I have a pair of factory set SM models as replacements.

You may not modify pneumatic parts.

Is calibrating really modifying?

As you are well aware the inspection checklist explicitly requires this switch to be checked that it shuts off the compressor at the appropriate pressure. I see no harm in allowing teams to adjust these rather than forcing them to purchase new ones when a small adjustment will fix the issue. It seems wasteful.

I think that depends on the switch. As pointed out before, the old Nason pressure switch is not meant to be user set.

The gap in my spark plugs isn’t meant to be user set either. They are a certified technician only job. But I adjust them every time I install new plugs and my car keeps running.

If you are saying I can’t adjust a set screw that is designed to be turned with a screw driver because it is modifying a pneumatic component, then we all have to stop using NPT fittings because they deform when threaded together. And push to connect fittings as well because the o-ring and barbs change shape every time a piece of hose passes through them.