Service Air Tank check valve

[Towbarman]

Good afternoon
Towbar here again for another question to ask. On our service sheet, it has service the 2 air tank check valves and the front emergency gladhand check valve. I know I have units that don't drain their air tanks after they drive them. When I go out and check the tanks, moisture shoots out about 2 feet. With the moisture/ water build up in the tanks, it does go through the lines and the check valves to a point that the valves are rusted and the one way flapper doesn't work. I guess I might be answering my own question here. Would the mechanic need to disconnect the lines and the check valves to see if any rust build up is present, and disassembly clean it out, spray a little lube in it and put it back together and install? Any ideas will help. Thank. Towbarman

 

[GeneralDisorder]

First of all - upgrade your air dryers to the newer style Haldex PURest dryer and service them every 6 months or you will be buying new air compressors like they are going out of style.

Second - you don't service those valves you just replace them. They are inexpensive Haldex parts. There are two back at the primary and secondary air tanks, one for the front emergency glad hand, and three two-way check valves behind the driver's step curtain. Replace them ALL. After you service/replace the dryer of course which should be dropping all the water before it even gets to the primary and secondary air tanks (or the "wet" tank for that matter). I daily drive my truck, only drain my tanks once a week or so and I basically NEVER see any signs of moisture. Hardly even a hint of fog from them. Actual water from the tanks is BAD and if the truck is properly serviced and leak-free so it's not cycling the compressor and dryer every couple minutes you really should never see anything.

And if you have that much water in your system you need to rebuild the brake treadle valve, the CTIS pressure control unit, and if you have any A1R trucks you should install desiccant filter cartridges before the MMDC transducers or you'll be looking for a new MMDC to the tune of $1200 when those fail.

 

[Ronmar]

Yea either replace the dryer, or at the very least clean and service your old style dryer. I did a youtube vid on servicing the old style dryer. Search “rronmar” on youtube to find my vids.

The principal of coalescing hasn't changed in centuries and the old style dryer actually has a lot going for it in terms of design. Tge new style is easier to service but requires a replacement cartridge to do so…

Moisture in tanks means one of two things:
1: Dryer is not removing it(needs service).
2. Dryer is being overflowed due to leakage and cannot keep up( find and fix leaks).

If yours is an A0, odds are its wet tank is not plumbed correctly anyway and it is only seeing ~1/5 of the air going to the brakes when it should be having all of it flow thru the wet tank to get to the service tanks. I can put up pics showing what i am talking about later. In a working/ or perhaps an overworked system, the first place you should ever see moisture is at the wet tank drain port...

the service tank checks are easy to test and inspect. the check at the front emer gladhand , not so much…

test:
Run truck till tanks are full dryer purges. Pressure should be 125PSI. Shutdown truck and drain wet tank. Monitor pri/sec. Rear/front pressures on the gauge. One tank dropping may indicate a check leaking back to wet tank. Close wet tank drain, wait a while and re-open the drain. Any air buildup in wet tank is most likely from a leaking service check.

inspect:
Drain all tanks! On inboard end of service tanks disconnect the lines or line to the fitting on the check valve. Using two large wrenches unscrew end cap of check valve from check valve body. Inside you will find a disc with rubber seal and a spring. Inspect these for rust, pitting, corrosion, rubber seal decay or debris. If corroded, replace if ok, Clean rubber disc and seat and end cap o ring and re-assemble. I put a little silicone GREASE on the end cap o ring.

just did this this weekend, had wet tank drained working on cab suspension plumbing and noticed primary pressure drooping and a tiny flow back into the wet tank.

found a piece of thread sealant from the compression fitting that had made its way to the valve seat. Cleaned that off re-assembled and no leaks during wet tank drain test.

the front check is a pita, so might as well replace it. The test for leakage, is with full tanks, remove the vented cover and seal the red glad-hand port with your thumb and see if any air pressure builds up.

that's why the front glads get vented, if sealed a leaking check could use tank pressure to release your park brakes…

 

[GeneralDisorder]

I will add that being an FD truck - the newer style cartridge dryer is more likely to actually BE serviced since it only takes 5 minutes and a new cartridge vs the old style that you have to essentially remove from the truck and spend at least an hour servicing assuming you have a new bag of desiccant - literally no one but an owner-operator with lots of time on their hands is going to go through the process of cleaning and drying desiccant to service that old unit.

 

[Ronmar]

yep, or a VFD with more man-hours than budget... lotsa ways to fry this fish

 

[Ronmar]

If this is an A0 truck, I suspect your air tanks are not plumbed properly. Every one I have encountered so far has been wrong. They fixed it on the A1 trucks.

The wet tank is supposed to be inline after the air dryer to act as another dryer/filter stage like its name implies. In order for this to work, all the air must flow THRU it. On the A0 they T‘d it off of the dryer output line running right to the service tanks, so the only time the service tanks see wet tank air is when the brakes are used while the compressor is NOT running, so only a small fraction of the service air ever sees the wet tank.

The good news is, it is easy to fix as seen in these pics, you simply swap two lines at the wet tank. Which probably explains how it happened in the first place, simple mistake…

You can also see the primary service tank check valve in these pics...

Wrong way:




Correct way: