1976 Palm Beach
Air Suspension Holding Valves
Why my bags never go down
The PO of my GMC installed these holding valves
This pic shows new brass fittings I bought to repair air leaks
This article pertains to GMC motorhome homes equipped with the original Power Level System. Many GMC Motorhome owners who have Power Level complain that their air bags leak down over relatively short periods of time. I have the Power Level and my air bags never leak down! Even after months in storage they still don't go down. In fact they will go over a complete winter without leaking down. I thought that they were all like that. Now I find that the Power Level System seems to be notorious for leaks.
What is the secret? Nothing that I did for sure. The previous owner installed holding valves in the air line from each OUT port of the Power Level Rotary valve to each airbag. The ignition powers the valves so that when the ignition is on air can travel to the air bags. When the ignition is off the valves close and air is trapped in the air bag. The beauty of this system is that each air bag is isolated from most all of the plumbing that has leak potential to keep them from deflating when the ignition is off and the various leaks take their toll. I know I have leaks with the rest of the system because my air tank will leak down overnight, but not the bags. This of course assumes that there are no leaks in the air bag and between the air bag and holding valve. That is normally only two fittings vs. the maze of fittings on the other side.
The valve appears to me to be the same "2-Way Normally Closed Solenoid" used in the newer Electro-Level systems.
I used to think all GMC's had these installed to prevent leak down. However, I've never seen them on any other coaches that I have looked at.
A mechanic at Cinnabar Engineering told me that these holding valves were something that Clarence Buskrik installed on coaches years ago.
Power Level Diagram drawn by Alex Birch in '76 taken from bdub.net (submitted by G. Kosier?)
Power Level Diagram drawn by Alex Birch in '76 edited to show Holding Valves.
Now you might ask what keeps the air bag from going down when the ignition is on (solenoid open) and air tank empty. The answer is there is a check valve in the height control valve that keeps the air from going back to the Power Level Rotary valve.