Norgren venting opening leak

[Fratto]

Good Morning and Happy 2021~

The lower norgren in the drivers bay is leaking air out of the bottom discharge or vent opening. This valve appears to be serving accessory things like:
Optional kneeling
Door lock
Drivers seat
Air horns
Etc.

I assume that this is a valve failure not a control issue? Anything I need to know before I replace my first one?

Also, since these accessories have their own control, what is the valve doing? Why not just feed all of these things from a manifold? Or is the kneeling option being used as part of the HWH leveling system?

Thanks!

[PrevostNewbie]

Are you saying the lower valve (bottom of stack) in the bank of 5? Those are the Level low system. Or is it one of the stand alone valves?

[Fratto]

It is the valve circled in red. The leaking discharge port has the red line pointing to it.

[PrevostNewbie]

On my Bus that is the Air Control and Exhaust Valve. The port you are pointing to is the air Exhaust port for Level Low. If i want to dump the air or lower the bus, the air exhausts there. Air can escape from that port if either the valve is shifted or partially shifted, or leaking. The air supply for that valve comes from the valve above it. if the dump switch is on or you are lowering the bus. This is a good exercise, we can learn together.

[Fratto]

Thanks Mike. I will confirm that this valve is operating like yours in the next couple of days. In the mean time, my valve is discharging even with the level low in drive. You can hear it when you turn off the diesel and it continues until the auxiliary air pressure goes to 0.

[PrevostNewbie]

If it's a slow air leak the spool is shifted partially or the seals are leaking. I just aired up my bus and soaped the ports and no leaks. next i asked someone to push the down button on the Prevost Level low and air came rushing out of that port (port 3) . When you dump air does it rush out of that port like it should? The air supply for that valve is the one above it. It's a spring return single pilot valve. When dumping air, the spool is in the spring shifted position. When you want to manually raise the bus up, the air pilot signal shifts the spool over. This pilot signal comes from the top valve and whtever position you are in at Prevost level low. The prevost level low selector switch will select one of the norgrens in the bank depending on which position. Top in the bank is Air Control & Exhaust, second down is Front Control, Third down, Middle is Drive, 4th down is Rear Right control, Last Valve is Rear left Control.

[Joe Camper]

Mark it's been my experience that when you have air seeping out the exhaust port on that lowest 2-position norgren in the steering Bay with the key off the problem is not with that particular valve. what's happening is your suspension in one of the three corners is leaking down and the valve at that particular corner of the suspension is what's bad and it's exhausting out that exhaust port in the steering Bay. When you hit the down button in level low for any of the three corners that's the port that exhausts the air so it's like you're on the down button when you're not if that makes any sense.

Are you sure the front suspension isn't losing air? I asked about the front because if it were the left or right rear norgren leaking out through the steering Bay it would be obvious you'd see the lean. You don't see a lean when you have a front leak and it's bleeding out in the steering Bay. It's going to be the 2 position norgren right above it or 1 of the 2, three position norgren's in the left or right rear that's what's gone bad.

DISCLAMER. The possibility exists I could be wrong. I've repaired this same situation a half dozen times as described but thay never stop posting new failures on a regular schedule. The way u say your aux air pressure drops is interesting. U would need that control coil on the manifold AND that lower norgren both to be bad togeather suppose it could happen. What else?? Maybe somthin

With all pressures up turn the key on but do not start. Dump all your suspension all 3 corners. Turn the key back off. Bet the leak stops and with aux air and brake tank air still present. If it stops then start up again and just air the front suspension up and turn it off again and listen. Repeat process for all 3 corners till u recreate the leak to see what corners causing the leak. Try that.

[PrevostNewbie]

Joe, do you think it's possible for the accessory air coming in on port 1 is leaking out port 3? That seems to be the only way accessory air can exit port 3 while in drive mode and exit port 1. I am trying to wrap my head around how air can come from port 1 on the front ride height valve and pass thru the air control and exhaust valve. In drive mode air pressure is on port 14 which allows air to flow into port 3 and out of port 2 to the ride height valve.
Air Control and Exhaust Valve (Lower Valve)
Port 1 Accessory Supply
Port 2 open when air on port 12
Port 3 open when air is not on port 12

Front 5 way 3 position air control Valve (Upper Valve)
Port 1 pressure Supplied from Port 2 valve below
Port 3 from front ride height valve
Port 5 plugged
Port 14 from Drive Norgren Prevost switch in Drive mode
Port 12 from front Control Norgren
Port 4 Plugged
Port 2 to air bags

[Joe Camper]

I think what I said. You're two buses are a generation apart the upper valve on your bus is a 3 position On Marks bus the two valves on the back wall are both 2 position valves. Anything beyond the explanation long-winded one I tried to keep it as short as possible we'll just do nothing but confuse everybody even more most everyone anyway.

[Fratto]

Joe, I dumped the air from all three corners and the bottom norgren continued to discharge through the vent opening. The primary and secondary brake air pressure remained steady, the accessory air went down to 0 and the air discharged stopped.

A couple more notes:

1) When dumping air, the discharge is way more than the leak we are discussing.

2) If you push the level low up button to raise either of the three corners the air discharge will quit. As soon as you release the up button, the leak will resume until accessory air pressure is 0.

I have never had one of these valves apart. Can they fail with a slight leak between ports 1 and 3? When it is leaking, it has a whistle not a whoosh which makes me wonder if it is a small internal failure allowing the accessory air to bypass to the discharge opening.