[77newell]

The compressed air system on your coach consists of two major sub-systems; the braking system and the suspension and other uses system. These systems are supplied by one common supply pipe that can be hooked to various sources of pressure with the engine pump always there. The two sub-systems are separated by a PPV (pressure protection valve) so that preference is given to maintaining air pressure to the braking system. Unless the pressure in the brake system is above 65psi no air is supplied to the suspension system. Since you have trouble getting above 50psi I think you have a leak in the braking system. A quick check of the automatic drains on the three air tanks would be a good starting place. I've also had the pressure relief valve on the rear tank (the only tank with one as far as I know) leak like crazy.

It is possible that the PPV has failed open and that then leaks in the sub-system feeding the suspension could be limiting pressure buildup. One indication of this would be if the supply gauge and the brake gauge pressures rise together. On my coach the brake gauge will rise slowly to about 65psi and then the supply gauge will rise very quickly as the PPV opens. Another way to check this is to close the two valves on the bulkhead just ahead of the rear axle that supply air to the front and rear suspension. If the air pressure now comes up within a few minutes then the PPV is bad and you have leaks in the suspension sub-system. (What I've titled "suspension sub-system" includes more than just the suspension, it includes air doors, gen slide, stair slide, air horn or any other use than for the brakes)

Let us know what you find and we'll help from there.