Leveling valves

[mung]

I know there has been some discussion about the leveling valves, but I still don't quite understand the failure modes.

So the leveling valves are 2 way right?  Bus is aired up and sitting fairly level.  Shut it down and the driver's side leaks air causing that side to lower.  Shouldn't the passenger side then be out of level and releasing air to try to compensate for the driver's side being down?  I know I need to find the leak on the driver's side, but I think I also need to find out why the passenger side isn't compensating right?

[bevans6]

They are called leveling valves but what they really are is "chassis height relative to axle" valves.  On a lot of buses there are two at the back and one at the front.  The two at the back set the chassis height above the axle - if the valves are set correctly then the chassis height is equal on both sides, and if the bus is sitting on a level piece of firmament, then the chassis will sit level side to side.  At the front the air springs on the two sides are inter-connected and the front side to side level just follows the rear axle setting.  The front leveling valve sets the height of the front of the chassis above the front axle.  Again, if it's set right and the bus is on level ground the bus will be level front to back.

At the rear the two valves are completely independent.  If one side leaks down the bus will indeed tilt.  The front will simply follow the tilt of the back - that is so the bus chassis is never under torsional stress.   One thing you could do is to disconnect the line from the leveling valve to the air springs (or air beam if you have a beam).  Put an adaptor in there with a schrader tire valve, and air up the springs to some handy height, and see if they leak down without the valve connected.  That will point you towards what part you need to fix.



Brian

[mung]

Right and I have the 3 valve setup.  So if one side in the back loses air, shouldn't the other side be letting out air trying to level itself?

[bevans6]

They aren't leveling valves.  They have nothing to do with level UNLESS they are set up correctly and the bus happens to be on level ground.  All they do is set the height that the chassis sits above the axle.  Call them "ride height valves" and the name would be closer to what they actually do.  I have no idea why they got called leveling valves in the first place...    

Edit:  I had added a paragraph to my initial reply that tried to address this as well.  If I'm not making sense, tell me and I will try again...   

Brian

[HighTechRedneck]

Call them "ride height valves" and the name would be closer to what they actually do.  I have no idea why they got called leveling valves in the first place...   

Actually in many if not most or all manuals, they are called height control valves.

And just to mix things even further, some buses, like my RTS, use one valve in back and two in front.  But it all operates on the same principal.

[bevans6]

The good old three legged stool that never rocks...

Brian

[mung]

When I put my solenoids on, I can put a valve on the outlet of them that would allow me to air up the bag on it's own, might be worth doing.  The passenger side bags look pretty new in the back, I haven't taken a close look at the driver's side yet.  The ride height valves have their adjusters welded and I still need to see if there is another adjustment on the valve itself as some of them have.