Air pressure

[Coffey1]

Alright fmtv gurus, what pressure's should we be seeing at wet tank?

Mine builds to 145 then air dryer purges
Drops to about 90 and rebounds.
Mines a 6x6

Andy's go to 118 and purges. I believe his also restarts at 90 his is 4x4

Thoughts

 

[sandcobra164]

I have an FMTV air governor on my M923 thanks to SwampDonkey and it builds to 145 and drops to about 135 after purging. Cut in is around 110 or so. It's adjustable.

 

[Swamp Donkey]

Cut-out pressure should be around 125 psi. The differential between cut-out and cut-in pressure is set at 20 psi and is not adjustable. Set the cut-out pressure and the cut-in pressure will fall where it needs to be.

Unscrew the plastic cover on the end of the governor to get to the adjustment screw. Turn the screw CW to lower the pressure or CCW to raise the pressure. 1/4 of a turn equals about 4 psi. Your pressure is too high at 145 psi Ken. Safety relief valves pop off at 150 psi. The compressor has to do much more work for that extra 20 psi with almost nothing gained. Andy's could probably be bumped up a little.


Having said all that...y'all should really verify your pressures with a known to be accurate test gauge before making any adjustments. Comparing dash gauges between trucks isn't going to be very accurate at all. You might find that your gauges are just off and everything is set properly already.

 

[Andyrv6av8r]

We are both using gauges hooked directly to our wet tanks.

 

[Swamp Donkey]

We are both using gauges hooked directly to our wet tanks.

I just got off the phone with Ken and that's what he had told me. He's going to adjust it down a little to see if it holds at a lower pressure and we'll go from there. The only reason I suggest bumping yours up a little is to insure the CTIS stays happy since they like to see certain pressures.

 

[Ronmar]

Exactly what Swamp Donkey said The CTIS pressure switch is looking for around 115-117 PSI to close so probably wont function with 110...

 

[Andyrv6av8r]

Problem is my 1078, at the lower pressure, is and has always worked fine. He is the one having issues at the higher pressure. We were wondering if the CTIS is faulting out seeing 145 psi?

 

[Ronmar]

The CTIS pressure sw should close at 115 to tell the controller you have air, and open at around 89 to tell CTIS that the wet tank/air supply is exhausted. Is yours switch cycling with full/empty wet tank(yours may be shorted). Hard to say what issues 145 is causing, I am not aware of an overpressure control, but the system could be looking not to exceed a max pressure on the pressure sensor on the PCU during its initial shot of air. For safety, I think CTIS will fault if you look at it crosseyed rather than proceed under questionable conditions...

Reset it to 120 and see if it works...