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It is probably not a coincidence that on a 406 Unimog those subsystems are all "beyond" the over-pressure valve. That's the valve that allows air to pass only after reaching a preset pressure. 70 psi comes to mind. The purpose, of course, is to delay supply to secondary functions to preserve primary functions, like brakes.
I had to replace the over-pressure valve on my LMTV a couple of times due to leaks, and guess what, it uses the same over-pressure valve design as the 406 Unimogs. I used a 406 OPV on the LMTV last time I fixed it. I looked at several here this evening and there were subtle differences in body shape but size and threads were the same.
The OPV is simple. Two screws and the cap comes off, but watch for the spring. The caps tend to warp and cause a leak, often pressure sensitive. I have made a thin paper gasket and used a little sealer to fix them
On a 406 the OPV is inside and near the left frame rail near the rear of the cab, "T'ed" into a main air line.
Bob