Air dryer bypass

[tumbo1]

have had several problems with the air dryer on my 04 columbia replaced whole sysem twice and it started to leak air again so i got sick of it and just took the two lines going into it and put them together and bypassed the air dryer now everything works great will this be ok as long as i keep draing my air tanks to get the water out.

[allan5oh]

No, it still won't be ok. The air dryer gets rid of moisture in the air, draining your tanks won't do anything to the moisture that's already in the air.

Sounds like a purge valve problem, or the valves on your air compressor. Where does it leak from? I'd work on fixing the problem, rigging it like this is just asking for trouble.

[bob h]

Originally Posted by tumbo1

have had several problems with the air dryer on my 04 columbia replaced whole sysem twice and it started to leak air again so i got sick of it and just took the two lines going into it and put them together and bypassed the air dryer now everything works great will this be ok as long as i keep draing my air tanks to get the water out.

NO, get a competent mechanic to repair the problem. if your purge valve is having repeat failures, i would recommend an air compressor blow-by test

besides moisture, the dryer also removes oil vapour which causes damage/swelling to air valve seals

what exactly are you referring to as the whole system?

[tumbo1]

it leaks from the block that u screw the air dryer cartridge into one of the valves under there there are 2 it is the one in front did older trucks have air dryers on them i dont remember my old truck having one just sick of replacing parts on the air dryer have had it replaced 2 times in one year.

[JoeyB]

IF I understand this- you build air to the cut off, shut the truck off and walk around and hear the dryer leaking. If that's the situation, then the problem isn't the air dryer. The wet tank check valve is leaking. That allows air that is already in the tank to sneak back to the air dryer and exit out of the dryer's purge valve, which should be open any time the compressor is unloaded.

By all means, I would keep the dryer in the system. It's true, we didn't have them until the '70s or so, but brake pneumatics were so much simpler then, and even at that, it was not unusual to freeze up in cold weather. With anti-skid, and all the rest of it, I'd definately do whatever I could to protect that air system, cause once it's contaminated, I have no idea how to clean it.

[bob h]

Originally Posted by JoeyB

IF I understand this- you build air to the cut off, shut the truck off and walk around and hear the dryer leaking. If that's the situation, then the problem isn't the air dryer. The wet tank check valve is leaking. That allows air that is already in the tank to sneak back to the air dryer and exit out of the dryer's purge valve, which should be open any time the compressor is unloaded.

By all means, I would keep the dryer in the system. It's true, we didn't have them until the '70s or so, but brake pneumatics were so much simpler then, and even at that, it was not unusual to freeze up in cold weather. With anti-skid, and all the rest of it, I'd definately do whatever I could to protect that air system, cause once it's contaminated, I have no idea how to clean it.

not sure of the make of this dryer, but most bendix dryers used a check valve as their outlet port (to the wet tank). although, this is not the only cause of an air dryer leak; the purge valve uses air pressure against a piston to hold it's exhaust port open, and again the cut-off valve can leak out the purge valve... the cut-off valve is integral to the purge valve.

[tumbo1]

it is not only when the tanks are at the cutoff it is any time there is air in the tanks if i put my hand over that valve on the air dryer it stops leaking. i had to bypass it just to get it home because it would not hold over 50 psi but once i bypassed it it was fine held about 125 and built up right away.

[bob h]

Originally Posted by tumbo1

it is not only when the tanks are at the cutoff it is any time there is air in the tanks if i put my hand over that valve on the air dryer it stops leaking. i had to bypass it just to get it home because it would not hold over 50 psi but once i bypassed it it was fine held about 125 and built up right away.

purge valve

can you buy a separate purge valve for this dryer?

when you drain the tanks, do you have lots of water? how 'bout oil?

[JoeyB]

What bothers me about this is that he's on his 3rd dryer. That's why I went looking elswhere for the problem.

[tumbo1]

no water comes out i checked the tanks and th valves on the tanks they look in good shape and i could hear no leaking the truck is an o4 so everything is in good shape yet i called freightliner and can buy the whole air dryer system for 287 so i am picking it up today and putting it in i will post once i am done thanks for all the help

[bob h]

Originally Posted by JoeyB

What bothers me about this is that he's on his 3rd dryer. That's why I went looking elswhere for the problem.

agreed... that's why i asked about "oil passing" or blow-by.

[bob h]

Originally Posted by tumbo1

no water comes out i checked the tanks and th valves on the tanks they look in good shape and i could hear no leaking the truck is an o4 so everything is in good shape yet i called freightliner and can buy the whole air dryer system for 287 so i am picking it up today and putting it in i will post once i am done thanks for all the help

let us know!!!

this is one of those ones i'd love to get my hands on ;0)

...should be a simple fix.

[tumbo1]

just finished the install not bad for 287 dollars kit came with new valve the one that goes by the air tank new hardware new cartridge and of course the new block were all this screws into took about 1 1/2 hours and now it all works perfect the valve on the front of the old block was toast looked like it was blown out compared to the new one thanks for all the help guys really appreciate it.

[GRANITE957]

I have a similar problem with a 02 Mack Granite. If and when the dryer works properly, it sneezes every 15 seconds. Most of the time, it is simply blowing thru the dryer. Since the system feeds off the manifold, it reduces my manifold pressure by about 5 to 10 lbs, therefore reducing my power. Occasionally during blow-thru, it will sneeze and suddenly my manifold pressure rises. Also the airdryer will blow through or sneeze no matter the air tank pressures. The shop cant figure out the problem. Almost every part from the compressor to the dryer has been replaced. A couple weeks ago after putting up with endless blowthrough and no manifold pressure, I had the dryer filter replaced. There was no blowthrough for 2 days, but it sneezed every 15 seconds like clockwork. If you bleed the tanks, there is no residue expelled. I had the airdryer bypassed last year and there was no problems and manifold pressure was normal. But, the water buildup in the tanks was impossible to keep up with and freezeup became a problem come winter, so the bypass was removed. Could use some good advise!

[heavyhaulerss]

Originally Posted by GRANITE957

I have a similar problem with a 02 Mack Granite. If and when the dryer works properly, it sneezes every 15 seconds. Most of the time, it is simply blowing thru the dryer. Since the system feeds off the manifold, it reduces my manifold pressure by about 5 to 10 lbs, therefore reducing my power. Occasionally during blow-thru, it will sneeze and suddenly my manifold pressure rises. Also the airdryer will blow through or sneeze no matter the air tank pressures. The shop cant figure out the problem. Almost every part from the compressor to the dryer has been replaced. A couple weeks ago after putting up with endless blowthrough and no manifold pressure, I had the dryer filter replaced. There was no blowthrough for 2 days, but it sneezed every 15 seconds like clockwork. If you bleed the tanks, there is no residue expelled. I had the airdryer bypassed last year and there was no problems and manifold pressure was normal. But, the water buildup in the tanks was impossible to keep up with and freezeup became a problem come winter, so the bypass was removed. Could use some good advise!

I have the same problem was told purge valve. replaced that. 69.00 did nothing to change the purging every 7- 15 seconds. put rebuilt compressor. still no different. put entire bendix dryer on. no difference. no one can tell me how to fix. got tired long ago paying for process of elimination fixe's

[GRANITE957]

Tumbo1 wrote in this thread the he "just finished the install not bad for 287 dollars kit came with new valve the one that goes by the air tank new hardware new cartridge and of course the new block were all this screws into took about 1 1/2 hours and now it all works perfect the valve on the front of the old block was toast looked like it was blown out compared to the new one thanks for all the help guys really appreciate it. " He went over his system repeatedly, but didnt discover the "blown out valve on the front of the old block" until he installed the kit. I think a better explanation of this discovery would be worth looking into with my scenario. Thoughts, experiences, and knowlege shared will be appreciated...

[GRANITE957]

The Mack dealership/shop said they never heard of such a problem. The company shop that works on this Granite, the mechanics, are at their wits end. They are a hard working bunch but not overly experienced. Typical R&R and PM mechs. You would think that these air dryer problems and resolutions would be documented with as many drivers who seem to share the same problem. I am the type of driver who will drive on old 220, so long as its giving me all it got. An engine (of any size) that isnt performing as it should simply pisses me off. Guess I will keep digging. Let you all know how it goes. Meantime, should anyone have anything to share on the matter...LET ME KNOW. Thanx - Larry