air dryer

[heavyhaulerss]

I am not sure what causes the air to dump when it reaches a certain psi, but mine dumps air every 7 seconds. both in dash air gauges stay on 120 psi. they dove move or fluctuate. they stay at 120 while driving at hiway speeds. 55-70 mph. i put on what i think would be called an air govenor. it mounts to the air compressor & has a couple air lines connected to it. the air govenor has not changed anything. even at an idle the air dumps every few seconds. the air dryer is original equip. 13 years old. since ive eliminated the govenor(the cheapest part to replace) would the air dryer be the next thing to replace or could something else be making my air pop off so frequent?

[Part Time Dweller]

http://www.bendixvrc.com/itemDisplay...ocumentID=5091

Not sure what model you have, but here is a PDF manual for the AD9 dryer. Scroll down to page 14, which is the trouble shooting guide. The first section should help you diagnose the purging problem, even if you do have a different model as they all function about the same.

[Kranky]

Also, the air pressure governor receives it's pressure from the "wet" tank just after the air dryer.

If there is a leak in the wet tank or lines leading to it, the wet tank pressure will drop quickly, causing the air governor to cycle the compressor on, then when the pressure reahes 120 in the wet tank, the air governor cycles the compressor off by sending pressure to the compressor unloader. The control line to the air dryer purge valve is connected to the unloader line and this pressure also causes the air dryer to purge each time the governor cycles the compressor off.

You would not notice a wet tank pressure loss on your dash gauges because there are check valves at the primary and secondary air tanks "downstream" to keep the air pressure from leaking back toward the wet tank, and the gauges read the pressure in the primary and secondary tanks.

[Bobby]

Service the air dryer. I do mine every 2 years in a dry climate.

[heavyhaulerss]

thanks for that link. very informative info. the ad9 is the type i have.

[heavyhaulerss]

I had the bottom element replaced but that made no difference. not sure if it was supposed to. a shop told me it may take care of it. was not sure if a air dryer is something you replace or just service. or if my purging problem can be solved by putting new air dryer on. i checked for leaks & could not find any on the sys comcering air dryer or lines. only air leak found was on air bag & a couple small leak on some fittings in other places. no where near compressor,govenor .et.c.

[pdm]

If you can, put a shrader valve on the governor port that is marked R'
ES or directly into the wet tank & hold the air pressure above 120-130psi.with the engine off.

You should be able to hear the leak. Whenthe engine is runnin ou can't hear the leak, when its off the pressure in the wet tank drops below the governor cut in pressure, thats why it sems like there is no leak .

It may be the compressor unloader vakve & it may help to take the inlet hose off the compressor to hear the leak bettor............hope this helps.

The wet tank is the one the airdryer discharge hose goes to & may be part of another tamk (2 tanks that look like one)

[Blind Driver]

since we are talking air driers....

Mine goes "shhh shhh" every 3-4 seconds. Sometimes I can even feel the truck move with each "shhh". Sometimes the drier will will fart normally, but mostly it's jst "shh shh" every 3-4 seconds. Maintenance has probably not been done on this air system in some time.

Any ideas?

[YerDaddy]

I used to rebuild my AD-9 every 4 years but now it is cheaper to buy a whole new unit than the individual rebuild components.

[Rev.Vassago]

I used to rebuild my AD-9 every 4 years but now it is cheaper to buy a whole new unit than the individual rebuild components.

Hypocrite.

[Jumbo]

If you think it is the air dryer rather then rebuild it throw it away and buy a new one. If this doesn't cure problem next step is to throw entire truck away and buy a new one.

[bob h]

I am not sure what causes the air to dump when it reaches a certain psi, but mine dumps air every 7 seconds. both in dash air gauges stay on 120 psi. they dove move or fluctuate. they stay at 120 while driving at hiway speeds. 55-70 mph. i put on what i think would be called an air govenor. it mounts to the air compressor & has a couple air lines connected to it. the air govenor has not changed anything. even at an idle the air dumps every few seconds. the air dryer is original equip. 13 years old. since ive eliminated the govenor(the cheapest part to replace) would the air dryer be the next thing to replace or could something else be making my air pop off so frequent?

If the air dryer is not serviced every couple of years, it can cause damage to abt everything in your air system.

...as for the purge cycling of the dryer, that is likely caused by an air leak upstream of the pri/sec air tanks.

[sbatson]

I can tell ya that mine did the samething and its had a new governer and dryer and everything that goes with it and guess what it still F%#$ING does it so what the other posters said about air leaks up stream is more that likely the problem so dont waist your money untill you check that out. My question is where should I start to look at?

[Larry227]

Could also be the unloader valve in the compressor. If it doesn't work right the compressor doesn't unload and keeps pumping so it keeps purging out the drier.
What model of drier do you have and what compressor?

[sbatson]

Well the dryer number that I found was AD-9 and the compressor was P23535190, is that what you needed?

[pdm]

Is there a schrader valve on the governor or the first air tank sfter the dryer?

[allan5oh]

I've seen compressors cause that exact thing, the valves in the compressors.

Also, I service my air dryer(purge valve and dessicant) once every fall.

I've seen far too many trucks stuck when the purge valve stays open, draining all the air. This is from moisture. Not going to happen to me.

[Kranky]

It's always a good idea to determine in advance what type of fittings it would take to bypass the air dryer in an emergency, then carry said fittings (and the necessary tools to perform the bypass) along with you on the truck.

That would enable you to keep going until you can get somewhere to fix a stuck purge valve.