What is going on with my air system?

[Gypsyman]

Fired the truck up from its winter slumber this morning. Popped right of and everything seems good to go. Shut her down and walked back into the office. That's when I heard it. It sounded like a timed release of air in a hard line. I walked back out in the shop thinking something was going on with the air dryer on the shop compressor. Nope. It was coming from the truck. Every few seconds an internal pssssst sound from the air tanks. No idea what is going on and I don't remember ever hearing this sound after a shut down. What am I missing?

I'm fully prepared to be called an idiot on this one so blast away.

Short video of what I'm hearing...

- YouTube

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

www.youtube.com

 

[HDN]

That's interesting... I wonder how much your truck's air gauge moves with each puff. Could it be a failing air pressure relief valve? I think there should be one at the air tanks.

 

[Gypsyman]

It's an odd one for sure. It's not an external release of air. Definitely inside of a metal line. I've placed my hand on every fitting and no air is being released at any of the tank fittings. It seems that the metal lines and the tank body are amplifying the sound. It's so slight that the gauge doesn't move at all. Over the course of 3 hours the gauge didn't even drop 5 psi.

I've cycled everything that is air related with no change at all. No air escaping under the hood or anywhere else. Started the truck and got it back to full pressure 3 times with no change.

Here's the best part....

Not 5 minutes after I made the post it just stopped all by itself. I was sitting in the office and noticed that the shop was quiet. I'll leave it overnight to see where the air pressure ends up and try it again tomorrow.

At this point I think it's just messing with me for leaving it parked.

 

[m715mike]

My truck made strange noises before the airpack failed. But it wasn’t exactly like the sound in the video you posted.

My airpack eventually failed when using a power bleeder to bleed the breaks.

 

[Crazyguyla]

Sounds like pressure being released through the vent lines.

 

[M35fan]

When my air pack failed, it was losing pressure through the vent line. Mine didn't lose it in small regular bursts, however. It was more of a constant air dump. My symptom was, it wouldn't build pressure past 60 psi. When I connected a compressor to the trailer supply and back fed pressure, I was able to find my leak exiting through the "slobber tube" by my engine. It made a very similar sound to the metallic psssh in the video. I can't understand why yours is short bursts, however. I'm interested to learn what the cause is.

 

[Gypsyman]

I'm wondering if it could be the check valve between the tanks? Maybe as one tank bleeds down slightly the check valve lets out a small puff of air towards the tank with the lower pressure. After sticking my head right up by the ends of the tanks it sure sounds like that's where the sound is located.

 

[rustystud]

That sound is normal. It's just the tanks equalizing. Heard that sound a thousand times in my career.

 

[dmetalmiki]

Rusty has it pegged...One of mine does exactly the same

The truck actually "Told me".. "Oh Stop worrying,".."I am juss' imitating a STEAM ENGINE waiting to pull out!".

 

[HDN]

I've never noticed my truck making this noise. Then again when I've had it out for a drive it's usually for its only drive for the day, so I immediately drain the air tanks after I park it. Next car show I take it to I'm going to have to remember to listen for this!

 

[Gypsyman]

That sound is normal. It's just the tanks equalizing. Heard that sound a thousand times in my career.

Thanks rustystud. So it sounds like I was on the right track with it being the check valve between the tanks. Nice to know that I'm not starting the season out chasing a ghost.

 

[rustystud]

Thanks rustystud. So it sounds like I was on the right track with it being the check valve between the tanks. Nice to know that I'm not starting the season out chasing a ghost.

On the transit buses they had up to 12 air tanks, and if the door tanks (which where the last to fill) leaked the whole system would slowly leak down groaning and squeaking all day long !
After the buses came in at night the "Yard" would make this racket for hours.

 

[Floridianson]

Can not remember if it was a TM but you can check to see if the check valve between the tanks is holding correct. Drain the outer tank of air if I remember and the inner tank should hold air pressure for the airpack with no leakage into the outer tank.

 

[Gypsyman]

Thanks Floridianson. I'll dig in again and see if I can locate the test procedure.