Aux Air Regulator Valve dumping Air at 70psi

[Bluthebus00]

Hey everyone, I'm a newbie here. We have a 25' Bluebird transit style bus. It has air brakes, suspension and a kneeling feature.

The auxiliary air regulator valve tied to the kneeler starts dumping air once the front tank reaches exactly 70psi. I bought the rebuild kit(part #RN17Y) for the regulator valve but that didn't make any difference at all. The valve is rated for 20psi and is adjustable. I've tried different adjustments on the valve after installing the new o'rings, spring and diaphragm from the repair kit but it made no difference what so ever.

The bus starts, pressurizes the tanks up to 70psi, the hissing begins from the regulator valve, the compressor tries hard to outpace the air being dumped from the valve but only manages to climb about 0.5 psi per minute

Any tips from mechanics? I have a Hendrickson air system. The regulator valve I'm referring to can be found here:

OEM part# N15817A (What's currently installed)
Repair kit: Haldex part# RN17Y
Replacement part# KN31040

https://www.haldex.com/en/na/valves-...table/kn31040/

[Booyah45828]

You wouldn't happen to have the lines flipped? That will cause what you're describing to happen.

Don't just flip em and re-test though. Trace the lines running to it and make sure they are where they're supposed to be.

[Bluthebus00]

Hey! Thanks for the reply! I definitely didn't flip the lines though. I took pictures and labeled all 4 lines before touching anything.

This wasn't an issue last fall running the bus. We went through the winter without starting the bus at all. Come February when the temperature randomly jumped up to 80 degrees, I started the bus and surprise, the valve was leaking...

Are there any tips for adjusting this valve I may have missed?

I'm also wondering if there may be a blockage somewhere this regulator valve is feeding causing pressure to rise and it ultimately dumps the access air pressure?

I was able to confirm it does primarily service the kneeler solenoid on the bus but tracing the lines shows it feeds other things as well.

[Booyah45828]

None of the busses I've worked on have air suspensions or kneeling features.

Those regulator valves are pretty simple. So if you're sure you rebuilt the valve correctly and all is well with it, I'd make sure that none of the other items that receive air from it are bad and back-feeding tank pressure back into it. That will also cause it to leak.

I don't think a line blockage would cause it.

What you could do is dump all of the air, remove the outlet hose from the valve and plug that port with a gauge. Air the bus back up and that will give you the pressure the regulator is set at. You could then monitor the hose and if there is any air coming out of it you know that something is back feeding on that line.

When you have it plugged and the valve is still leaking, then you know the valve is bad and either have to try to rebuild again or replace.

Around here, new/rebuilt air valves are easier to source then a rebuild kit, so most are just replaced.

[Bluthebus00]

Thank you! I will definitely give that a shot. And report back with my findings. As I was reading your post, the manufacturer also returned my inquiry suggesting the same.

[Bluthebus00]

The repaired valve is functioning properly and stepping the pressure down to 20psi.

The cause for the regulator valve dumping the air was it was unable to pass air through the line connected to the outlet port. There was some back pressure coming off that line when I disconnected it. I plugged the outlet port with a pressure gauge and read 20psi and let the system pressurize to it's cutout point.

When the bus went to blow off the access pressure as its supposed to at 120 psi, it blew out a ton of water. Looks like I didn't drain the system good enough before letting it sit for the winter.

I then let it to pressurize itself to the cutout point when it blew off pressure and moisture, cut the engine off, then bled the tanks and air dryer. Repeated the process 3 more times until everything was bone dry.

Removed the pressure gauge, reconnected the hose to the outlet port and let the system re-pressurize. No issues now and no leaks! The kneeler even works again!

Did an air brake test in the driveway, timed the cut out and cut in refill rate then I was off to take a glorious drive through the neighborhood. Back on the road. Thanks so much for your suggestions! It helped me confirm the valve is working correctly and also helped me find the cause being a 1/2 bled air system.