Earlier today I was going to get my first load of sand and I drove onto the scale/silo and set my brakes.A minute or two into the loading process the low air light comes on.I finish getting loaded and drive over to the area where we can roll are tarps up and start looking for a leak with the truck off but find nothing.I end up idling up till the tanks are at 90psi and start driving down the rural road leading away from the sand plant.The highest PSI I got was 100.When I made it to the site I got in line behind a bunch of trucks and every time a truck moved forward I released the brakes and the low air light would come on.Just finished unloading and pulled off the site to an empty site down the road and checked everything again with the truck off.Also with the wheels chocked and brakes released.And with the key in the on position and found nothing.What could be causing this?
Some leaks will stop when the air system gets below 90-psi... Put air up all the way to 120 psi and shut engine off, then key-switch back to on position, jump out before it drops back down.
(04-27-2021 )Rawze Wrote: [ -> ]Some leaks will stop when the air system gets below 90-psi... Put air up all the way to 120 psi and shut engine off, then key-switch back to on position, jump out before it drops back down.
The only way it goes up to 120 is if I drive it above 55MPH.
Do you think the tractor (or trailer) emergency brake valve is having as issue? Air blowing past the diaphragm when it's under pressure (brakes released).
Last year, I had that issue. Losing air like crazy when going down the highway...literally watching the tank drop and rise, over an over while traveling. When I would pull over, set the brakes, I couldn't find the leak anywhere. Reason being, is that it would only leak when the emergency brake for the tractor was released.
Set your trailer brakes and release the tractor and see if you hear the leak. If that's what it is, it will be leaking substantially.
**edit - just re-read the last line of your first post. Sounds like you tried this already.
You could air up the system with shop air and then try different things ie. Brakes on, brakes off, splitter up/down etc.without the noise of the engine.
(04-27-2021 )Redland1 Wrote: [ -> ] (04-27-2021 )Rawze Wrote: [ -> ]Some leaks will stop when the air system gets below 90-psi... Put air up all the way to 120 psi and shut engine off, then key-switch back to on position, jump out before it drops back down.
The only way it goes up to 120 is if I drive it above 55MPH.
then it will not pass a 112-point D.O.T. inspection!. .. you need to get that air system fixed right away, as the truck is dangerous!.
If it will not get to 120-psi at idle, then the air dryer/govenor is shot!... that or the compressor!
(04-27-2021 )SquareOne Wrote: [ -> ]Do you think the tractor (or trailer) emergency brake valve is having as issue? Air blowing past the diaphragm when it's under pressure (brakes released).
Last year, I had that issue. Losing air like crazy when going down the highway...literally watching the tank drop and rise, over an over while traveling. When I would pull over, set the brakes, I couldn't find the leak anywhere. Reason being, is that it would only leak when the emergency brake for the tractor was released.
Set your trailer brakes and release the tractor and see if you hear the leak. If that's what it is, it will be leaking substantially.
**edit - just re-read the last line of your first post. Sounds like you tried this already.
Even when I started it up this morning it took forever to get to 90 psi with the rpm at 1100
(04-27-2021 )Rawze Wrote: [ -> ] (04-27-2021 )Redland1 Wrote: [ -> ] (04-27-2021 )Rawze Wrote: [ -> ]Some leaks will stop when the air system gets below 90-psi... Put air up all the way to 120 psi and shut engine off, then key-switch back to on position, jump out before it drops back down.
The only way it goes up to 120 is if I drive it above 55MPH.
then it will not pass a 112-point D.O.T. inspection!. .. you need to get that air system fixed right away, as the truck is dangerous!.
If it will not get to 120-psi at idle, then the air dryer/govenor is shot!... that or the compressor!
Yeah I parked it last night after I got unloaded.Heading to the mechanic shop now.Now that you mention it the air dryer was purging a lot and now I can’t hear it purge at all.
The mechanic put his hand over the compressor outlet and he held it with no problem.He said when it’s working correctly you can’t hold it.Is this true?