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Strange Governor Behavior


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I have a strange air leak problem for you today.  My air system is in pretty good condition overall, not perfect, but plenty safe enough.

When I’m loaded on the highway and start up a moderate to heavy pull, I will sometimes hear a really loud air leak start up.  I immediately check the gauge but the thing is sometimes it’s not losing air, it’s gaining air.

This has happened a few times and I’ve realized that the sound and the rate of gain/loss is related to the amount of boost I have.

It doesn’t keep going forever.  It will fill the tank up to 120psi and then the dryer will purge and the problem will go away completely.

if I let way off the throttle and reduce the boost it will start losing air.  It has always happens at the worst possible times when I am hurrying so I haven’t tried to see what happens if I let it leak back down below 100psi.  I don’t want to know.

The compressor intake is connected to turbo air so is it possible I’ve got air leaking backwards through the manifold? And then something about the purge cycle causes a valve to get unstuck?

why does it start in the first place?  Maybe high boost after the compressor cut out is putting pressure on a weak valve and it gets pushed into some strange intermediate position.

It has only happened about 6 times in the past month so it’s hard to pin down.  It can start at any pressure between 100-120 psi.  One time I was sitting at maybe 118 and it started, purged, and went back to normal in a few seconds.

My air compressor is ancient, but my air dryer and governor are NEW.

I appreciate any advice or suggestions, thank you.

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Posted (edited)
19 minutes ago, zeault said:

I have a strange air leak problem for you today.  My air system is in pretty good condition overall, not perfect, but plenty safe enough.

When I’m loaded on the highway and start up a moderate to heavy pull, I will sometimes hear a really loud air leak start up.  I immediately check the gauge but the thing is sometimes it’s not losing air, it’s gaining air.

This has happened a few times and I’ve realized that the sound and the rate of gain/loss is related to the amount of boost I have.

It doesn’t keep going forever.  It will fill the tank up to 120psi and then the dryer will purge and the problem will go away completely.

if I let way off the throttle and reduce the boost it will start losing air.  It has always happens at the worst possible times when I am hurrying so I haven’t tried to see what happens if I let it leak back down below 100psi.  I don’t want to know.

The compressor intake is connected to turbo air so is it possible I’ve got air leaking backwards through the manifold? And then something about the purge cycle causes a valve to get unstuck?

why does it start in the first place?  Maybe high boost after the compressor cut out is putting pressure on a weak valve and it gets pushed into some strange intermediate position.

It has only happened about 6 times in the past month so it’s hard to pin down.  It can start at any pressure between 100-120 psi.  One time I was sitting at maybe 118 and it started, purged, and went back to normal in a few seconds.

My air compressor is ancient, but my air dryer and governor are NEW.

I appreciate any advice or suggestions, thank you.

I have had air driers do this were you chasing this before the air drier change ? ! Was the problem before the new drier or after ?! I am a fan of the Bedix AD9 air drier Tried and true in my mind!

Edited by fjh
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I guess the air dryer isn’t that new.  It was installed by the previous owner when I bought the truck because the original dryer seized.  That was in November.  About a month after it was installed I had a problem with it purging every 5 seconds and that turned out to be a bad check valve on the dryer.

Maybe I’ll call the guy and tell him to get his money back. Hah

Ill figure out what model I have when I get out there.  Could this be another replaceable valve or is it better to just get rid of the whole dryer assembly?

thanks

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