best place to tee into bus air system?

[bevans6]

I will be adding a quick connector so that I can easily add or take air from the bus system (1980 MC5C).  I was playing around with filling it from my compressor on the weekend and noticed that if the air dryer had just purged, I couldn't add air at the ping tank and there was no pressure there to draw air from either, since the air dryer was effectively disconnected from the wet tank by the check valve at that point.  My next idea is to add an air chuck at the drain valve on the accessory tank up front.  Easy to get to, and the accessory tank is connected to both the parking brake tank and the dry tank.  I think all the check valves will allow air into the accessory tank (obviously), the parking brake tank and the dry tank - but there is a check valve between the dry tank and the wet tank that should block air from going into the wet tank, or further back towards the compressor/ping tank.  Does anyone see a problem with this?  I feel that if I can get air into the accessory tank, the parking brake tank and the dry tank, I should accomplish my goal of basically being able to air up the bus without starting the engine, plus be able to easily draw air out to fill tires, maybe work the impact wrench, etc.  

I know that the emergency fill valve up front only goes to the parking brake tank, and no further, plus there is a one way check valve on it so that no air can come out of it, so it's not a valid choice for this.

What am I missing?  Can you think of anything wrong with this not filling the wet tank?  What about putting air into the suspension air filter backwards?  What will the pressure protection valve do if the pressure on the accessory tank side is higher than on the dry tank side?  Will they even pass air backwards?  I am loath to introduce a modification that taps directly in to the dry tank, since that might introduce a brake system failure point.

Brian

[TomC]

For using air pressure off the bus system, use any tank after the wet tank (first tank after the compressor).  For filling the system, just install a Schroeder valve on the wet tank (like a tire stem valve).  Good Luck, TomC

[buswarrior]

are you trying to suck and blow at the same time?   

sorry, couldn't resist... 

I'd be inclined to fill the air system via the wet tank, and take your air off downstream. Using the same point introduces a significant compromise: moisture someplace you don't want it, in the coach or in your tools.

You don't want to be introducing the wet from your aux compressor into the dry parts of your air system.

Or you'll be posting about non-functioning air components once the freeze is on.

The discharge muffler location will accept air just as soon as the governor calls for air pressure at cut in, and will continue to do so unless your aux takes the pressure beyond cut-out. As you know, you can force cut-in with a couple pumps of the brake pedal.

Why do you need air in it before cut-in?

As for taking it off, the aux tank under the driver gives a nice clean supply that is easily accessible.

happy coaching!
buswarrior

[TomC]

I thought I just said that.

[buswarrior]

Yes, you did!

[Fredward]

My MC-5A does not have an air dryer. But I Teed off right at the ping tank and put an air chuck there as well as a male fitting with a valve. When I want to air up with shop air I just attach the air hose to the male fitting and turn on the ball valve. Handier than a Shroeder valve I think. I've never taken air out there but the suggestion to put the air chuck on the tank up by the driver is an excellent one because it might be kind of wet back there.

Fred

[Just Dallas]

Removed

[buswarrior]

Only if it was manufactured by Schrader.

Kleenex versus facial tissue

It is a popularly used brand name, be careful, earlier MCI have lots more than tire inflation style valving from Schrader.

http://www.schrader-bridgeport.com/

happy coaching!
buswarrior

[gus]

 "My next idea is to add an air chuck at the drain valve on the accessory tank up front.  Easy to get to, and the accessory tank is connected to both the parking brake tank and the dry tank."

I did this on my 4104 and it works fine. I have a female chuck attached to the aux tank drain valve and a double ended male quick connect fitting which fits into the female chuck when I need to add air or drain the tank.

When I need air from the bus I connect my air hose to the female fitting.

You need a valve between the T or whatever you use in case the quick connect fitting should fail. Yes, they do fail!

I tried filling from the ping drain put it chattered the check valve. When I tried to take air from it it came in pulses. A total failure as a location.

[bryanhes]

I attached mine at the bottom of my ping tank over the weekend and it works great. Is there a difference in my system vs. the MC5C and 4104?

Bryan

[bevans6]

So the consensus advice is to separate the two functions.  Good point  about why would I need to add air before cut-in - I have no idea why, but true to form I tried to on the weekend and it didn't work, I thought it through to understand why it wasn't working but didn't think the rest of the way through to fanning the brakes to lower the pressure to below cut in.  I was thinking of the bus compressor and the governor as tied at the hip, it didn't occur to me that the governor would work the same with an external source of air.

I will just add a chuck with a ball valve at the ping tank, probably where the schrader valve is (The Schrader valve (also called American valve)[1] invented by August Schrader in 1891[2] consists of a valve stem into which a valve core is threaded, and is used on virtually all automobile tires and most wider rimmed bicycle tires. The valve core is a poppet valve assisted by a spring. - Wiki.) to add air, and add a second chuck at the accessory tank to remove air. 

Brian

[bevans6]

Bryanhes, here is what my MC5C does with air at the ping tank.   The ping tank is between the compressor and the air dryer.  When the air pressure in the system reaches the governor's cut-out pressure (118 - 120 psi on my bus) the governor sends a signal to the air dryer to purge.  The air dryer purges and basically opens the line between the compressor, through the ping tank, up to the check valve on the air dyer line to the wet tank, to atmosphere.  The air dryer doesn't close the purge valve until it is signaled to by the governor going under it's cut-in pressure and causing the compressor to start supplying air again.  So on my bus the ping tank has pressure only during a compressor fill cycle.  Any time that the bus air system is between cut-out and cut-in pressure (between 90 psi and 120 psi, basically) the ping tank has zero pressure.   There is a one-way check valve on the air dryer so that air can never be drawn from the bus air system via the ping tank.  The only time you could draw air from the ping tank is the amount of air stored in the air dyer and the line to the air dryer, if the compressor is on a fill cycle.

That's how it works on my bus, anyway.  I don't know how your 4104 is set up, but if it has an air dryer, it may well be the same.  I would appreciate if someone with a better understanding of this can confirm that the governor signals the air dryer to close it's purge valve at cut-it, since I confess I have thought prior to this that the air dryer closed the purge valve immediately after purging. I didn't think it was left open between compressor cycles.

Hope this helps a bit.   Brian

[buswarrior]

Air drier remains in purge configuration (purge valve open) for as long as the governor stays in cut-out configuration.

The drier isn't ready to go for a half minute or so, There continues to be less noticeable air vented from the drier, drying the desicant for the next round of pumping.

It takes a pressurized signal line to accomplish this.

Note to northern busnuts, and those suddenly found in sub zero temps:

A good practice when expecting below freezing temps is to shut down with the compressor cut-in and pumping to avoid being stranded with a frozen purge valve on start-up.

When you shut down, the heating element stops being powered, if it is working...

Purge valve freezes open over time, preventing the coach from airing up when you fire it up.

On some air driers, the purge valve also blocks the compressor discharge line when in purge mode, so the compressor is pumping, no air leaks are heard, but no air is getting into the tanks.

Preventive maintenance is key!

happy coaching!
buswarrior

[bevans6]

Thank you for confirming the purge valve operation AND for the excellent tip!  I'll be driving in freezing weather soon and I will be following that tip religously.

Brian

[bryanhes]

When I drain mine the only air relieved is what is in the ping tank, so I assume there is a check valve at the tank. I am guessing it is routed a little differently because of the drier?

Bryan