Cracked Automatic Drain Valve

[gMw]

After a long winter nap, found the air pressure wouldn’t build up to it’s normal operating level, so couldn’t move the coach, bummer. Discovered a crack in the Automatic Drain Valve and have a new one on order (since my local Freightliner dealer doesn’t carry one). BTW, the valve itself is simple to replace. And I figured a simple way around the problem so pressure would build to it’s normal level.

Being the inquisitive type, I took the valve body apart, from what I can tell, the valve body cracked due to freezing, expanding water that wasn’t “automatically” drained off. Something new to add to my winter storage check list.

I find it interesting that the chassis has two air pressure tanks and only 1 Automatic Drain Valve, the other tank has a manual drain valve only.. Does anyone know why that is???

Also, this valve is electrically operated, does anyone know how and when this valve is automatically operated?

[Pigman]

Actually, the other tank has TWO manual drain valves. One is in the front and one in the back. The tank had a steel partition inside that makes it two tanks in one.

I suspect the only one automatic is because this is the first tank that receives air from the Air Drier. If the drier filter and desiccant have a problem, you'll see it first and the automatic valve may take care of most of it. By the way, there should be cable lanyards on all three tank valves that should be pulled at least on each 6 month service.

John

[gMw]

John, thanks for the reply… I’m aware of the cable lanyards, and manually draining the tanks.

Let me add a bit more information about the Automatic Drain Valve, a manual drains is mounted on the side of the Automatic Drain Valve assembly, approx 7/8 th of an inch above it’s base. The Automatic Drain Valve has it’s own water reservoir that’s below and not emptied by the manual drain. I’m thinking here in lies the problem… Hence my question about how and when this valve is automatically operated, thinking there might be a way to electrically force it to drain.

[Pigman]

George, my air system schematic calls that valve an Automatic Moisture Ejector valve and does not show anything actuating it. Could the wires be for a small resistance heater?

My only other solution would be to give the Freightliner Help line a call and ask them. I found the valve on Parts Pro, but cannot get any info out of the wiring diagrams.

John

[J Walker]

John, I have never drained water from the area of the automatic pressure release valve. If it was water that collected and broke your valve then there is something wrong. I have not read in my manual of a regular draining of water. Air periodically vents from the valve when I run the engine.

[gMw]

I called the Freightliner Help line, The person I spoke to didn't seem very knowledgeable about the part itself. I guess they don’t get many calls on an Automatic Drain valve. Anyway, they told me that it operates (drains) at the same time as the automatic drain valve on the drier.

$121.18 later, I now have a new Automatic Drain Valve sitting on my work bench. It’s easy enough to install, but I by-passed it so I could drive the motorhome while waiting for the new valve to arrive.

I’m not sure that I see a need to install the new one, as the manual drains work just fine.
FYI

[J Walker]

George, I am still unclear about where the pressure relief valve is located, but I believe that my drier has a pressure relief valve. When I buy a new drier a pressure relief valve comes with it.

[gMw]

Jim, in our chassis, there are two pressure tanks, mounted between the frame rails, pretty much in between the front wheels. The Automatic Drain Valve is mounted to the right tank, rear (back).

[Darryl]

The electrical connection going to the drain valve is for an internal heater. These valves come with and without the heater, depending on which you want. It is not otherwise electrically operated.

[mdga]

Just going over the fuses before leaving the cold for Florida. The fuse on the Automatic Drain Valve blows as soon s the key is turned on. I can hear a valve activating avery few minutes while running and I also pull the three manual drain cables frequently. Question.. Am I safe to run in freezing weather till I get down south where someone can look at it?
Many thanks,

Mike

[Elkhartjim]

Sorry Mike, but I'm having a senior moment I guess. Are you saying the drain valve is activating every few minutes and that even with the valve "draining" every few minutes you're continuing to pull the lanyards? First, if the fuse is blown and btw I wasn't aware it was fused, how is the valve activating? I would hope the fuse would cause the valve to fail in the fail safe mode...open.

The answer to your question, yes your safe to drive to FL if you're worried about the moisture freezing. I live in a humid area and pull the lanyards every 6 months or so and I've never seen more than a mist from the manual valve. My concern is if the automatic drain is activating every few minutes, will you be able to maintain air pressure.

[mdga]

Thanks for the quick reply. I'm only going by the circuit diagram on the Freightliner decal. Fuse is located behind the pullout just below and to the right of the radio. As mentioned, something releases air about every three minutes when at idle and I have no problem whatsoever maintaining air.
Your advice is appreciated.

Mike

[RobRV]

On an OTRT the correct Procedure includes draining the Primary (Wet) Tank at the end of the trip and again during the Pre trip Inspection! With the advent of Motor Homes and general Lack of Knowledge about Air Brake Systems by the Owners of said Vehicles the Automatic Drain Valves were developed. They can fail resulting in an accident!
There is or should be a legal requirement to manually drain the wet tank. this ensures that the One Way check Valve is working correctly and will expose any problems with the air Brake System.
For those that have taken an Approved Air Brake Course this subject was covered in detail. For those driving Air Brake equipped Vehicles who have Not taken a Course, Please do so as soon as possible!
MDGA the Air release that You are hearing is the result of the Pop Off valve actuating. This Valve prevents the Compressor/Governor from creating Too much Pressure and damaging the Air Brake system. This has nothing to do with draining the Wet Tank!

[Elkhartjim]

Morning Rob. I don't know where or who taught your "air brake" course, but I'm afraid you got some bad information. I don't have time to discuss now, but before you scare the bejabbers out of somebody I wanted to post my comment.