Daily air brake pressure bleed

[Joel Weiss]

I'm the proud new owner of a 2000 40' Beaver Patriot Thunder (CAT-12, coach #53267) and I'm quickly trying to learn proper maintenance procedures for the vehicle.  I do hold a CDL and one of the things I was taught was to bleed the air brake tanks each day to remove accumulated water vapor.  The previous owner of the coach did not know of any way to drain pressure other than via the air dump switch on the dash.  It is my understanding that this switch is designed to dump the air bags but there is no mention of it being related to the brakes.

I found a reference in the Magnum owner's manual about bleeding the brakes every day from the vehicle "control panel" but there is no further description of exactly which valves and I'm afraid to simply open things without knowing what I am doing (especially when it relates to brakes.)  In the electrical compartment area I did find a valve body with attached air lines that looks like it is involved with the air system and there are what appear to be two adjustable "needle valves" but, again, I don't play with things I don't understand!

Any assistance will be greatly appreciated.

[Richard And Babs Ames]

If similar to ours (1997 Patriot)  on the passenger side rear  in the bay behind the batteries you may have a series of 4 valves and a disconnect for an air hose. You should be able to drain all air storage from this location manually and hook up an air hose if you like.  

The daily draining is for vehicles without an air dryer which you should have. Depending on your location you may want to service the dessident canaster and coalsing filter.

[Joel Weiss]

Thanks for the quick and helpful response.  I do have the valves where you said they would be and my manual does refer to an air drier.  Checking the desiccant is probably a good idea.

As long as we're on the subject of "air" can you give me some guidance on air "usage" by the coach when driving?  When the coach is off and parked there is a modest air loss over a couple of days, but the pressure remains above the brake safety level for quite a few days.  Ideally, the loss should probably be even less but this seems manageable.  However, when we are driving I have noticed that the air pressure will drop from 120 psi to ~100 psi every minute or two and then be restored by the compressor system.  The loss rate is far less than the compressor's recovery time so that isn't an issue.  It does seem as if the loss rate is related to the roughness of the road so I assume that there must be some air being "used" as the coach levels itself during travel.  Is this a correct assumption?  Is this loss rate higher than normal?  If so, by how much?

[Gerald Farris]

Joel,
The air dryer should be working OK, if you do not get any water from the tanks when you bleed them. Some coaches do not run the bleed lines from the bottom of the air tanks, so to properly bleed them, you need to go under the coach and bleed some air from the bottom of the tank, by loosening a valve or plug in the bottom of the tank. This probably only needs to be done once or twice a year, and if you get water, service your air dryer.

However, if your air compressor is cycling every minute or two, that is excessive. You should check the compressor and air dryer purge valve for proper operation.

Your coach only uses compressed air for the suspension, and as a boost for the hydraulic brake system. Since your coach has hydraulic brakes instead of straight air brakes, it will use much less air volume with brake application, than a coach with air brakes, but it also has a little smaller air tanks than the air brake coaches. However, with an eight air bag suspension, it will use a good bit of air, when it adjust the ride height.  

Gerald  

[Joel Weiss]

My air valves are in the engine service area (last compartment on the passenger side).  Do you have any idea where the drier, purge valve and desiccant would be located?  The valves themselves are "stiff" and difficult to turn.  I wouldn't be surprised, if one of them has a slight leak.  I've "wiggled" them a bit in the hopes that might help.  We've gone around the coach after running the engine and pressurizing the system, and there is no audible leaking sound.  I think you're right, that it is a slow leak from a valve or maybe a compressor air line.

[Gerald Farris]

Joel,
Your air dryer should be located in the engine area bolted to the right frame rail. I would not jump to the conclusion that you have and air leak. The air dryer will exhaust a small amount of compressed air every time the compressor unloads (quits pumping). This exhausted air is used to purge the water that has collected in the air dryer.

Idle the engine until the suspension reaches normal ride height and the compressor unloads, then turn the engine off and monitor the air pressure. If you have a leak the air pressure will drop or the suspension will drop in height.

Gerald