Air line problem
 

Air line problem

Started by eaglekelly, January 04, 2009, 04:14:08 PM

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eaglekelly

January 04, 2009, 04:14:08 PM
   I need help understanding the operation of the air compressor unloading circuit. I ran into this while tracking an air leak thru the bendix air dryer. When the compressor reaches its operating pressure there a blast of air thru the bottem of the dryer, which is normal I think, but after the inital blast, air continues to leak slowly at the same spot till the compressor cycles again. I pulled off the small air line coming from a valve attached to the side of the compressor going to the dryer and air is leaking from this point. I can put my finger over the line and the leak stops and remains stoped till the next cycle. I replaced the valve on the side of the compressor but to no avial. While I had the vavle off I found that the opening attached to the compressor is blocked by a screw in plug. The only other line coming into this valve is another small one coming from the front of the bus which I haven't tacked down yet. I'm wondering if the valve (unloading Valve?) was installed correctly in the beginning. I've run into several things that were not done properly by the previous owner.
   The bus is a 1979 Eagle with a 6V92 engine installed.It has always had the leak since I've owned it but I just found that it was coming out of the dryer a couple of weeks ago.

wildbob24

#1
January 04, 2009, 04:55:27 PM
EK,

The valve you are talking about is called the governor and controls the unloading of the compressor. One of the small lines should run from an unloader port on the governor to the dryer. The other line should run from a reservoir port on the governor to the air tank. The hole in the compressor, under the governor mounting, should not be plugged.

This link will explain more:

http://www.bendixvrc.com/itemDisplay.asp?documentID=2382

If it's been a while since your dryer has been serviced, that probably need to be done, as well.
P8M4905A-1308, 8V71 w/V730
Custom Coach Conversion
PD4106-2546, 8V71, 4sp
Greenville, GA

buswarrior

#2
January 04, 2009, 06:58:27 PM
The small line from the governor, which is bolted to the side of the compressor, should be pressurized when the air pressure reaches cut-out, and should be empty when the pressure drops below cut-in.

This pneumatic signal is what activates the purge valve in the air drier. In effect, it pushes it open, and lets it close again.  Only the volume of air in the drier should be allowed to escape when it purges.

The problem you are having is with the air drier's internals leaking air. Get a rebuild kit for the purge valve, and do a service on the air drier while you are at it.

happy coaching!
buswarrior

Frozen North, Greater Toronto Area
new project: 1995 MCI 102D3, Cat 3176b, Eaton Autoshift

eaglekelly

#3
January 04, 2009, 07:14:58 PM
   Thanks, that's the info I needed. I did take the dryer apart and clean everything up. 'Finally found those big orings that were leaking in the dryer from WW Grainger. The local truck parts place said that parts were no longer avaible for my big old Bendix unit. He wanted to sell me a new small canister type for about $230. I may go that way in the spring. By the way, on the side of the unit it says not to mount it in the engine compartment and thats right where someone stuck it. Is that a real problem?

luvrbus

#4
January 04, 2009, 07:20:00 PM
Eaglekelly, you can still get parts for the AD-2 dryer I get parts for mine at NAPA for my Eagle and it is mounted in the engine compartment came from Eagle that way    good luck

buswarrior

#5
January 04, 2009, 07:24:03 PM
Emphasis on "he wanted to sell you..."

As noted, parts are still available, and there are many of the AD1/AD2 originals still working just fine out there.

You need a minimum mileage of airline between the compressor and the drier in order for the compressed air to loose some of the damaging heat. The drier also benefits from being a cool can to help with condensation.

Just through the bulkhead to a cooler location, and preferably in the wind somewhere would be better.

Bendix has the details on their site.

happy coaching!
buswarrior

Frozen North, Greater Toronto Area
new project: 1995 MCI 102D3, Cat 3176b, Eaton Autoshift
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