M1088, Brake Pressure too High Venting from High Pressure Relief in Air Dryer

[ke6rwj]

Hey all, been working on the air brakes on this truck for some time. when I bought this truck it had 1500 original miles (yes really) the fifth wheel still had factory paint and not a scratch... it would not build brake pressure past 60psi at all, so with help from this forum I was able to determine the cause, 2 frozen check valves behind the tanks due to a corroded air dryer passing moisture.

I replaced the following in July-aug
- Governor
- Air Dryer
- rear brake inversion valve
- 2 check valves

The truck got up and running, and had been fine. Now the system will not Purge air via the dryer or stop building air pressure. An air gauge on the tanks shows 150 when the valve blows, and keeps climbing, but slower. These are both linked to the governor (a new one btw) so I wanted to confirm everything else was working before I blame the governor.

Purge line to dryer
I removed the governor and checked for trash etc, Removed the air purge line from the dryer and blew clean compressed air through it to make sure it was clear, then re-hooked it to the dryer and blew air in again and the purge valve activated on the dryer.

Wet Tank Line
Removed this line from both sides and cleared the line made sure there are no restrictions or trash in the governor..

What say you all? governor?

Chris

 

[coachgeo]

...
What say you all?

Chris

Could a few hoses be plumed it wrong places? would not be the first time a hose has been found to be plumbed into the wrong place!

 

[simp5782]

So the purge activation line is not or is getting air thru it from the governor when the air pressure at the governor is at or above 125psi?

If no, verify air pressure the governor is seeing to ensure it has or has no air pressure. If yes and is seeing air pressure replace the governor. If not then check supply lines for it.

If you have air coming down the purge line at 125psi but it won't purge then it's a dryer issue

 

[ke6rwj]

Could a few hoses be plumed it wrong places? would not be the first time a hose has been found to be plumbed into the wrong place!

yea, It was working then stopped...

 

[ke6rwj]

So the purge activation line is not or is getting air thru it from the governor when the air pressure at the governor is at or above 125psi?

It is not getting pressure as I can tell.. and I confirmed that the line is clear and drying is working by applying EXTERNAL air to the line to see if it purges..

If no, verify air pressure the governor is seeing to ensure it has or has no air pressure. If yes and is seeing air pressure replace the governor. If not then check supply lines for it.

its kinda tough to see what pressure that is at directly unless I plumb in a gauge. Im not quite sure there is another way to do it.
So here's what I have,,
I'm seeing 155++ air pressure in the tanks, and the truck builds air pressure to the brakes, so that says the check valves between the tanks and the Governor pressure line are clear. Also I unhooked the pressure line to the gov at both sides to make sure its clear. This should mean there is pressure on the governor. unless you know a more direct way?

If you have air coming down the purge line at 125psi but it won't purge then it's a dryer issue

I confirmed the air dryer is working via external air test on the purge line.

 

[simp5782]

It is not getting pressure as I can tell.. and I confirmed that the line is clear and drying is working by applying EXTERNAL air to the line to see if it purges..


its kinda tough to see what pressure that is at directly unless I plumb in a gauge. Im not quite sure there is another way to do it.
So here's what I have,,
I'm seeing 155++ air pressure in the tanks, and the truck builds air pressure to the brakes, so that says the check valves between the tanks and the Governor pressure line are clear. Also I unhooked the pressure line to the gov at both sides to make sure its clear. This should mean there is pressure on the governor. unless you know a more direct way?



I confirmed the air dryer is working via external air test on the purge line.

Pull the line off the dryer. The signal line. If there is no air when the air pressure hits the governor preset. Then move to the governor. Remove the lines from the governor. Start the truck. See which one has air pressure. Use that line and rig up a gauge to hook into it or by using a T fittings and air chucks. Ensure you have the correct pressure to the governor.

I bet the supply air pressure to the governor works on the pressure protection side of the system. So if the pressure protection valve isn't opening all the way then the governor can't see the correct blow off air pressure. This happens on the 939 series trucks when the pressure protection valve freezes up with water and the compressor just runs till the pop valves release pressure

 

[Ronmar]

Sounds like the governor is not unloading... here is a way to check wet tank pressure without connecting a gauge, just hold the rubber point against the tank drain and open the valve... have you tried adjusting the governor?

 

[ke6rwj]

Pull the line off the dryer. The signal line. If there is no air when the air pressure hits the governor preset. Then move to the governor. Remove the lines from the governor. Start the truck. See which one has air pressure. Use that line and rig up a gauge to hook into it or by using a T fittings and air chucks. Ensure you have the correct pressure to the governor.

I bet the supply air pressure to the governor works on the pressure protection side of the system. So if the pressure protection valve isn't opening all the way then the governor can't see the correct blow off air pressure. This happens on the 939 series trucks when the pressure protection valve freezes up with water and the compressor just runs till the pop valves release pressure

Ahh ok, ill check those

on a side (safety) note, is it possible (or advisable) to start the truck with the cab tilted? I can access the Governor from the under the cab but this question has bugged me a bit...

 

[ke6rwj]

Sounds like the governor is not unloading... here is a way to check wet tank pressure without connecting a gauge, just hold the rubber point against the tank drain and open the valve... have you tried adjusting the governor?View attachment 815799

I'm still looking for the right size gauge for this, In the meantime I installed a airchuck on the far left tank to check pressure.... is it more accurate off of the wet tank, or does it matter?

 

[simp5782]

Wet tank

Yes you can start it with the cab raised

 

[Ronmar]

The Wet tank is where the governor samples air pressure rof control. Yes it is ok to start and run with the cab tilted, just be careful with the door if you have to open them so they dont over-extend and do damage...