Airing Up With Shop Air

[gus]

Tried to air up my 4107 today at the aux tank, went to 30 psi and stopped? Always did this on my 4104 with no problem.

So I aired it up at the main wet/dry tank, a mystery??

[Cary and Don]

Our 4107 has a valve at the aux tank that opens at 60psi.  Maybe they have yours set at 30psi?  We always supply air to  ours on the wet/dry tank when in storage.

Don and Cary
1973 05 Eagle
GM 4107
Neoplan AN340

[buswarrior]

I am theorizing here, so don't quote me...

To air up the coach via the auxiliary tank, requires that the air passes backwards through the pressure protection valve.

First of all, the pressure protection valve might be absent in some coaches. Then, if present, it's inner workings have to allow air to pass backwards when closed, in order to air up the bus this way.

If the pressure protection valve does not allow backwards air travel when closed, you won't be able to air up the coach via the auxiliary tanks.

It is interesting that you only got to 30 lbs, in which system are your gauges plumbed? Where did the rest of the shop air go? Aux pressurized to max, and rest of coach stayed low?

happy coaching!
buswarrior

[gus]

What makes this so interesting and puzzling to me is the 30 psi? This makes no sense whatsoever.

My understanding of the protection valve is that if the aux press drops to 60 the valve is supposed to close off the aux system to preserve the remaining dry tank air for the brakes. Based on that there is no logical reason the hi pressure shop air shouldn't flow from the aux tank to the dry tank.

When I aired through the aux tank the suspension bags aired up completely and shortly after that the air stopped flowing. I checked the dash air gage and it was only up to 30psi. I have no idea to where the gage is plumbed. It seems to it should be plumbed into the dry tank?

I don't know the pressure in the aux system because there is no gage on it. I assume it had to be well above 30 to air up the suspension and that it was the same as the shop air.

My 4104 gage is plumbed into the aux tank which is a bit confusing but a lot of things about that system were changed including the old ICC valve! I always air it through the aux tank because it is the easiest to get to.

[Eagle Andy]

Guys I don't know if this is related, but on my eagle I have a aux air compresser and i have this happen to me my compressior will run for along time while I'm doing othere things and i look at my dash gauge and I have 30 # so i step on my brake peddle and bngo air starts going into the system.

[buswarrior]

A pressure protection valve is adjustable, and can get lazy over time as the spring in it ages.

And it is designed to protect in the other direction from the way you are trying to air up the coach.

Depending on how its internals function, it may not allow air to pass, when the pressure on the side it is supposed to protect is too low.

There will also be check valves lurking in the system somewhere which may prevent it being aired up "backwards"

What year is your 4107? The 4107 may be functioning just as it should.

The 4104 would have been a single circuit system, and as you point out, heavily modified from stock. There's no telling what was or wasn't installed, and whether any of it was working as intended.

Just because the brakes work going down the road doesn't mean it is plumbed right for misadventure!

Or to air up backwards,

happy coaching!
buswarrior

[gus]

It is a '66.

I'll try that brake pedal method next time, interesting!

Also, when it stopped at 30 psi the DD3 parking brake would not release, no surprise there.

When all this happened I just started the engine and aired it up because I was afraid the whole system was messed up, worked fine. I didn't try shop air at the dry tank but will. It seems there is no way that won't work though.

[RJ]

Gus -

My 4106 had a quick disconnect plumbed into the "ping" tank back in the engine compartment for airing up the coach w/o firing up the Detroit.  Always worked when I hooked up the shop compressor to it, brought everything up to 110 psi, the shop compressor's limit.

FWIW & HTH. . .

[gus]

RJ,

My 4104 had the same thing but it didn't work! All it would do is pulse when I put the shop air to it?

Also, you can't get air out of it unless the engine is running!