leaking from bottom of foot valve

[robertglines1]

On the 98 prevost dual brake application valve I have a constant bypass of air coming out the side the green supply lines come into. There is a bypass of some kind there covered with a flat exposed diafram  type material.  The rest of the brake system --R-14 etc are new as are lines.  This a new event after sitting.  Don't understand it drains air down from brake system and auxiliary/2nd dairy systems.  Is slow leak.  My reasoning leaves some answers but some unexplained?  I would think it was internal to dual brake application valve  but  why drain both sides?  Any help thinking this thru is greatly appreciated.  this is a ABS /disc brake on steer and tag.    Hate to throw parts at it--actually most everything else is new.    One more thing the gauges don't  fall rapidly and will pass brake air test for loss and recovery.         Bob

[bevans6]

Most dual brake valves are configured about the same.  The primary circuit is on top, closest to the pedal or the application mechanism, and it sends air to the relay valve and works the rear brakes.  The secondary circuit is closest to the bottom and it sends air to the front brakes.  The exhaust port is on the bottom and it releases air from the delivery ports when the brake valve is released.  If you have a leak constantly from the exhaust port the air is coming either from the supply ports and leaking past an internal o-ring seal, or it's coming from the delivery ports and getting back-fed from somewhere.  Usually if it's coming from the delivery port it's the rear brake line coming in to the primary delivery port, only because there is no other source of air for the front brakes to back-feed from.  It could be coming from the relay valve, which always has a supply of air directly from the primary air tank.  What I would do to trouble shoot it is disconnect the primary circuit delivery line and see if the leak stops.  If it stops and there is air coming out of the delivery line, it's somewhere in the rear brakes.  If it still leaks, the air is coming from the supply lines and there is probably a leak inside the valve somewhere.

As I understand this stuff, anyway... 

Good luck,  Brian

[robertglines1]

Thanks;going to reread post about 3 more times. The fog is starting to lift! (in my head) First step is to make sure brake pedal has not engaged the E-15 slightly.  I just started and one of the variables is new floor in that area.  System is and has been moisture free as long as I have had coach.  Bob

[Raymond smith]

Could be leaking thru the rear brake pots. Happened to me on my semi i use to drive

[robertglines1]

update;depress pedal slightly and it stops. thinking it is internal to E-15 foot valve. Kits are available for around $80. Am assuming it is a seal on the spool inside valve that is bad. Probably from sitting several years and got brittle=move it slightly and it reseals. Sound reasonable?  Prob been sitting since fire (including time before I bought it) 7 yrs.  New E-15 $384.    Opinions/observations welcome.   Just saw Ray's post.  Should there be any air there if brakes aren't applied?    Bob

[bevans6]

If the parking brakes are set and the service brakes are not applied with spring brakes, should be no air in the rear cans.  If the parking brake is off and a diaphragm is leaking you can get feedback to the foot valve.  With spring brakes it takes full air pressure in the spring brake can to release the parking brake so there is always air present and available to leak.  If the parking brake is on, there is no air pressure to leak.  I think that with some brake systems you can get feedback air from the parking brake valve too.  Personally I would look around and get a factory rebuild valve if I could, they are somewhat complex inside and I wouldn't rebuild one.  Anyway, if you are thinking you are going to change it, take the delivery lines off first and air it up to see what is leaking with those lines off, just for fun.

With our race cars we have something called a "flotation test" that we subject certain parts to.  Brake master cylinders are one of those - toss it in the pond and it if floats, fish it out and rebuild it.  Usually they don't float...     Calipers on the other hand we rebuild, they can be a thousand dollars a pop if you have rare ones.

Brian

[brmax]

Maybe there is a reman on the shelf somewhere, is the "tag" still on it. You can always take it apart and look It either hits the trash or the core pile with the supplier, prices seem hi high in both options from here but I haven't looked around. Sometime they have a custom bracket or such keep us posted, a bummer though no matter.
Good Day

[luvrbus]

I decided to rebuild a E-10PR the pedal for a retarder transmission man was that a costly mistake on my part after 3 days I ordered a rebuilt unit 

[robertglines1]

A bit more info: I have the knor-brenske- tag emergency brake canned /they are brand new. And I forgot to pull the t-bolts . Shouldn't make a difference :but after reading Jon article on PC about recent bad knor-brenske parts from factory and them leaking from parking brake side to service.. I have a vague ?? unresolved.  Can't see where without the parking brake being released(air applied it) there is any possibility. The air should not be let past the R-14 unless told to do so.=brake released.   Any body got source for Bendix # 109174    E-15 foot brake valve. Prevost is $384.  another source was $440.    When it comes down to it I like to know reason why this condition exist. All control valves in system have been replaced (new). Will update conclusion. Hate to just throw parts at it.    I have/will reread replies to see if a light comes on in my head.  Bob

[luvrbus]

Bob there is cylinder in the bottom part that has 1 o-ring if that o=ring is bad they leak as that valve has a air chamber were air is always present like any foot valve does but you probably know this already