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Old 06-12-2012, 11:35 AM   #1
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How often should your air dryer discharge?

I have read allot of threads with no real answer on how often should a correctly working air dryer discharge? I am about to service mine because I think it might be discharging to often?
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Old 06-13-2012, 06:17 AM   #2
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I have read allot of threads with no real answer on how often should a correctly working air dryer discharge? I am about to service mine because I think it might be discharging to often?
They generally discharge when your air compressor cuts out at the preset pressure. Some driers however spit more often.
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Old 06-13-2012, 07:39 AM   #3
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Thank You for your response. The main reason I ask is when I am parked and no brakes are being used and no suspension is being adjusted the air dryer goes off about every ~90 seconds? This seems to be excessive to me but I may be wrong? I have checked for leaks on both sides with nothing just a small hiss out of the air dryer after a blow off before the valve seals again.

I have a 1998 Coachman Santara on a Freightliner XC chassis with a Midland Air Dryer that works quite well as I bleed my forward tanks with no water in them at all. I have never drained my wet tank as it does not have a relief on it currently.

Anyway I talked with my local Freightliner & Cummins dealers without getting any real answer so I thought I would ask the question here.

Anyway thanks for the reply, I will keep searching for an answer. JR
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Old 06-13-2012, 07:22 PM   #4
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Air Dryer discharge is a self -full-filling , when it discharges it takes in more air , when it takes in air it thinks it has developed water in the system and it discharges, I have no idea if it goes on a timed or pressure build cycle just, that's the way it is. Better than draining tanks daily; that would have to be done on a unit with out the dryer.
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Old 06-14-2012, 06:38 AM   #5
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I have no idea if it goes on a timed or pressure build cycle just, that's the way it is.
When the air governor unloads the compressor, it spits the air drier. In another thread, the poster had one spitting about every 20 seconds and what cured it was rebuilding the spitter valve assembly on the bottom of the air drier.
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Old 06-14-2012, 07:29 AM   #6
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I tested the Air Governor last night and the test proved that the governor is working properly.

How I know this is by letting the governor shut off the compressor at 130lbs then slowly press down several times on the brakes to lower the level of air until you see the gauge begin to climb again at about 110lbs.

What I noticed this time is allot of air loss from the spitter valve after the engine was shut off! I had not noticed this to be as extreme as before which leads me to believe that the Air Dryer needs to be rebuilt.

I found a great Air Dryer Troubleshooting PDF at Greatalarm.com which has been of great help in my efforts to figure out if I have a problem in the early stages developing or not. JR
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Old 06-15-2012, 09:00 PM   #7
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What I noticed this time is allot of air loss from the spitter valve after the engine was shut off! I had not noticed this to be as extreme as before which leads me to believe that the Air Dryer needs to be rebuilt.
Yep .... time to service the drier.
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Old 06-18-2012, 07:53 AM   #8
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Ok Here is an update

I purchased a upper and lower service kit and in just under 2.5 hrs I removed rebuilt and reinstalled the air dryer.

The upper service kit directions were very well written however the lower service kit directions left allot to be desired.

Two of the bolts on the purge exhaust cover broke off inside the housing and I had to drill them out to fix.

Anyway I reinstalled the dryer and ran it for over 15 minutes and the dryer worked perfectly. The only time it discharged is when I ran the brakes down so that the compressor would cycle and once it reached the 130# mark it purged.

Lesson learned my compressor was cycling way to often, not as bad as the guy who had his cycle every 20 seconds but my 90 seconds was not much better. Anyway Thanks to everyone who responded. JR
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Old 06-19-2012, 06:18 AM   #9
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Ok Here is an update

Lesson learned my compressor was cycling way to often, not as bad as the guy who had his cycle every 20 seconds but my 90 seconds was not much better. Anyway Thanks to everyone who responded. JR
Not exactly. Unless the air pressure got below about 100, the compressor wasn't compressing. The spitting problem was purely limited to the drier itself.

Unlike your A/C compressor, your air compressor runs all the time as it's gear driven. When it's valves are closed (as in cylinder head valves, it compresses air. When the pressure is up, the governor opens and sends air to the head and opens the valves so no more air is compressed.

Hearty congratulations on a nice piece of work!
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Old 06-19-2012, 08:30 AM   #10
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Cool

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Not exactly. Unless the air pressure got below about 100, the compressor wasn't compressing. The spitting problem was purely limited to the drier itself.

Unlike your A/C compressor, your air compressor runs all the time as it's gear driven. When it's valves are closed (as in cylinder head valves, it compresses air. When the pressure is up, the governor opens and sends air to the head and opens the valves so no more air is compressed.

Hearty congratulations on a nice piece of work!

I believe that my condition with the Air Dryer created a leak on the supply side so I did not see the pressure drop on the forward tanks past the wet tank and after the check valves.

Because so much air was leaking on the supply side and because I could not hear it with the engine running. I think the compressor was cycling allot more than needed. As the compressor cycled thats when the dryer discharged about every 90 seconds under no air use and even more often when in motion.

Now that I have rebuilt the leaking dryer, now the compressor only cycles when I am actually using air and therefore the dryer is not going off as much.

I thank you and everyone for your help in this as it has bothered me for some time and my instincts were correct. JR
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Old 06-19-2012, 07:12 PM   #11
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I believe that my condition with the Air Dryer created a leak on the supply side so I did not see the pressure drop on the forward tanks past the wet tank and after the check valves.
I'm certain you are correct
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