Post shutdown air release then pop

[50shooter]

Not sure what to call it and couldn't find anything on it searching either. One of my deuces (the one I drive a lot) makes a sound after shutdown that none of the others do. You can hear air evacuating with authority for about 20 seconds and then a distinct air "pop" and then all is quiet. It would seam to be a pressure relief on the compressor or something. It sounds official but why don't the others have it?

Any ideas?

Thanks

 

[FMJ]

Yes, my M35's do it, had me looking for a leak the first few times.

 

[AaronW]

Mine both have the "pop".

 

[joeypushjr1]

mine does it everytime i shut down . seems normal to me

 

[Floridianson]

Some have twin cyl and some single air compression systems and it relieves pressure two different ways.

 

[1stDeuce]

How often does your compressor run with the truck just sitting there?? Mine leaks down and the governor kicks (clunk, pop, hard click, whatever) within about 5 minutes of shut down. Could you have a gross air leak?? Of course, why would the leak stop immediately when the governor kicks. Someone who understands that system better than I will have to chime in.

Compressor shouldn't run a lot without you tromping the brakes... Mine runs about every 5 minutes with the engine running... That's a pretty fast leakdown as far as I'm concerned, but I can't seem to find where it's at. Mine seems to kick on at about 110, and off just over 120. Kinda tight control on air, but at least it doesn't get too low...

Good luck!
C

 

[oldshep]

comes from the air governor i belive

 

[Floridianson]

How often does your compressor run with the truck just sitting there?? Mine leaks down and the governor kicks (clunk, pop, hard click, whatever) within about 5 minutes of shut down. Could you have a gross air leak?? Of course, why would the leak stop immediately when the governor kicks. Someone who understands that system better than I will have to chime in.

Compressor shouldn't run a lot without you tromping the brakes... Mine runs about every 5 minutes with the engine running... That's a pretty fast leakdown as far as I'm concerned, but I can't seem to find where it's at. Mine seems to kick on at about 110, and off just over 120. Kinda tight control on air, but at least it doesn't get too low...

Good luck!
C

My trucks with one cyl system run all the time and the gov leaks off on the firewall. Twin cyl just relieve the pressure at the head of the compressor high side. and the gov controls dump valve. These are so far the only two systems I have seen on a Deuce.

 

[Floridianson]

Does everyone know what the have? 1 2 ?

 

[50shooter]

How often does your compressor run with the truck just sitting there?? Mine leaks down and the governor kicks (clunk, pop, hard click, whatever) within about 5 minutes of shut down. Could you have a gross air leak?? Of course, why would the leak stop immediately when the governor kicks. Someone who understands that system better than I will have to chime in.

Compressor shouldn't run a lot without you tromping the brakes... Mine runs about every 5 minutes with the engine running... That's a pretty fast leakdown as far as I'm concerned, but I can't seem to find where it's at. Mine seems to kick on at about 110, and off just over 120. Kinda tight control on air, but at least it doesn't get too low...

Good luck!
C

My compressor doesn't run to often. My air will stay up for a couple of hours after shutdown so guessing it isn't an air leak.

I'm sure it is just a pressure dump as it sounds normal and does it everytime. I'm going to have to double check the other trucks. They may be blowing the air off too but I just don't hear it on them.

Thanks for the quick replies.

 

[airmech3839]

mine does it too.

 

[nofearnohope]

Mine does it at shut down and periodically while I'm driving. Kinda sounds like the big rigs when their air systems do that quick "pssht" sound. (Yes, that is a real sound)

 

[Keith_J]

Unloader or governor on the air system. It could be a sign of an air leak.

 

[1stDeuce]

Hmm, so the single and twin cyl compressors are controlled differently?? Sounds like the single runs all the time, and excess is just vented, so to speak... I know mine is a twin cyl, and there is most definitely an unloader, and it starts and stops depending on pressure. Ok, the driven pulley spins all the time, but you can tell that once the pressure reaches target, it kicks out the actual compressor drive and isn't pumping 120psi anymore. (Isn't pumping at all, right?)

Cool.
C

 

[Keith_J]

Hmm, so the single and twin cyl compressors are controlled differently?? Sounds like the single runs all the time, and excess is just vented, so to speak... I know mine is a twin cyl, and there is most definitely an unloader, and it starts and stops depending on pressure. Ok, the driven pulley spins all the time, but you can tell that once the pressure reaches target, it kicks out the actual compressor drive and isn't pumping 120psi anymore. (Isn't pumping at all, right?)

Cool.
C

I thought the unloader just shut the intake valve, preventing any real volume from being compressed.

 

[Westex]

Well....mine pops approximately every 3 to 5 minutes when it's running, but I dont have the 'pop' sound at shutdown. Mine holds air for about 6 to 8 hours without the buzzer sounding at start up, but will not hold air overnight. After reading other posts here, I know I've probably got a small leak somewhere, 'cause I've read that the truck should hold air overnight. Just need to get to it.

 

[G-Force]

it sounds like your unloader valve is bleeding back. In other words, when you reach pressure it unloads the compressor and closes off the port in the valve that goes to the air tanks or system. The pressure is bleeding back through this valve and out the relief port. This is hy your compressor is cycling every 5 minutes...and also why you hear it hiss when you shut it off and then pop. The pop is the valve closing...and probably you.re losing your air during shutdown through your compressor...which is why you don't hear any leak....
Either that or you guys need to stop running your trucks on baked beans........

 

[m16ty]

Mine does it at shut down and periodically while I'm driving. Kinda sounds like the big rigs when their air systems do that quick "pssht" sound. (Yes, that is a real sound)

The sound you hear on the big rigs is more than likely the air dryer. They make a very loud "air dump" every time the governor kicks the compressor out.

All deuce compressors run the whole time the engine is running. They may not be pumping air but they are running. I had a old truck driver tell me one time that running an impact off the truck would wear out my compressor. I told him I don't see how it could because the compressor is running all the time anyway.

 

[Floridianson]

Hmm, so the single and twin cyl compressors are controlled differently?? Sounds like the single runs all the time, and excess is just vented, so to speak... I know mine is a twin cyl, and there is most definitely an unloader, and it starts and stops depending on pressure. Ok, the driven pulley spins all the time, but you can tell that once the pressure reaches target, it kicks out the actual compressor drive and isn't pumping 120psi anymore. (Isn't pumping at all, right?)

Cool.
C

It's still trying to pump up just can't build any pressure as the dump is open.
Pistons are still moving at all times. This is not like a AC system that has a magnetic clutch.

 

[stumps]

The sound you hear on the big rigs is more than likely the air dryer. They make a very loud "air dump" every time the governor kicks the compressor out.

All deuce compressors run the whole time the engine is running. They may not be pumping air but they are running. I had a old truck driver tell me one time that running an impact off the truck would wear out my compressor. I told him I don't see how it could because the compressor is running all the time anyway.

I can see a couple of ways: 1) When your compressor is pumping, any head pressure that leaks behind the rings forces them out against the cylinder walls. When it is idling, there is no head pressure, so the rings have only their normal spring pressure holding them against the cylinder walls. 2) When your compressor is pumping, it is concentrating the heat in the ambient air making it hot. That heats up the compressor's head, cylinder walls, and piston. If the compressor doesn't have adequate cooling capacity (fins, water jacket, fan...); it will likely overheat under continuous use. Remember, it was only meant to make up the air lost due to braking and air powered windshield wipers on a continuous basis.

It would take a research project to figure out what the compressor was intended to do beyond the brakes and wipers... that, or a thermometer

-Chuck