Air system: proper tank to tap accessories off of

[TheHubbardBus]

Right now we've got a pressure protection valve coming off the primary tank, going into a 1/4" line that feeds the air door regulator. This 1/4" line has also been tapped into (Tee), to feed the driver's seat. Is this right? I can see the door being almost as important as brakes, as w/o air it just flops open. But it seems the seat should not be on this circuit, even w/ the protection valve (think it's a 70psi valve, not sure though).


We're planning on adding an air-horn & maybe something else air-driven later. I was thinking I'd add a 2nd pressure protection valve off the wet tank, for these accessories, & move the seat over to that also, so the only thing coming off the primary would be the door. Does this sound like a solid plan?

[PNW_Steve]

As best I understand it:

The check valve is to protect the air system that feeds your brakes in case of a failure of less critical accessories. If your seat, door or other accessory should fail in a manner that dumps air you won't lose the air to the brakes.

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[TheHubbardBus]

Thanks for the input, Steve. It's not a simple check valve though, it's a pressure protection valve, so it will allow anything downstream of it to bleed the primary tank down to its pressure setting. I think this valve's set-point is 60 or 70 psi. For the door, maybe this is standard? But I don't think the seat springing a leak should be allowed to draw it down that low.

[Brad_SwiftFur]

The protection valve is typically set for 60 (I'm reasonably sure this is a minimum) but 70 is not unheard of, either by intent, or just wear and age (and is fine, under 60 is another matter). Virtually everything that's not stopping and parking brakes should on the protected side. I see no reason for a second valve since I doubt you'll be using the air door, air seat, air horn, air suspension, and whatever else all at the same time. You'll likely use one at a time, and none (except the horn) should use much air.


The reason all this is protected is because you never know when an air line will break or some seal will rupture and that's enough without worrying if you'll have enough air pressure to stop safely before the parking brakes engage. And you'll be surprised how quickly that pressure will drop even with a small line open.

[TheHubbardBus]

Thanks Brad.


70 psi is what I think it is, based off the part #, but the number is partially obscured, so I wasn't 100% positive.


I still don't understand why it's coming off the primary tank though (the seat, at least). That was the reason I was considering a second valve, not to support a lot of accessories, but so everything but the door was on a protected circuit off the wet tank instead of the primary. That's the way a generic system is shown in the Bendix handbook I'm using to try to figure all this stuff out (pressure protection valve off wet tank to accessories). Seemed like an extra bit of redundancy. It looks to me like the seat was added in sometime after the bus was built, so I was concerned someone didn't do things right. But if you see no problem with things the way they are, I'm sure they're gtg

[Brad_SwiftFur]

What you could do is find an air blower kit (common at truck stops) that connects into the air-seat plumbing, basically comes with a compression T-fitting, coiled air hose and blower "gun". Simple solution to a simple need. Of course you can still add an air outlet for tools and tires.

[Booyah45828]

Originally Posted by TheHubbardBus

I still don't understand why it's coming off the primary tank though (the seat, at least). That was the reason I was considering a second valve, not to support a lot of accessories, but so everything but the door was on a protected circuit off the wet tank instead of the primary. That's the way a generic system is shown in the Bendix handbook I'm using to try to figure all this stuff out (pressure protection valve off wet tank to accessories). Seemed like an extra bit of redundancy. It looks to me like the seat was added in sometime after the bus was built, so I was concerned someone didn't do things right. But if you see no problem with things the way they are, I'm sure they're gtg

Volume.

Opening and shutting an air door multiple times per mile will drain a wet tank in a hurry. Wet tanks are typically small in capacity. The way that it's ran, they have the door being fed by the capacity of the wet tank and the primary tank.

You're correct that you don't really want anything but brakes on the primary tank. But the air door is pretty important too, so running that off there isn't an issue as long as that protection valve is in place and out of the way so as not to be knocked off by road debris.

The air seat could have been an add on and was tee'd into the closest hose by a mechanic. Once again, it isn't an issue as long as the protection valve is there.

[BaconFarms]

I just read my service manual for my Gillig transit bus. It has four tanks, actually two with partitions. As follows;

Primary Tank-Rear Brakes
Secondary Tank-Front Brakes
Accessory Tank-Suspension, Doors, Seat
Wet Tank

So, on Gillig Advantage's, the doors are accessories and are linked to the suspension, etc., so being the doors opened almost every block in the city and sometimes the suspension was kneeled, it kept up. Also, the tanks are located above the driver in a bulkhead in the ceiling of the bus.

BaconFarms

[TheHubbardBus]

Sweet guys. Thanks so much!