-
Secondary Tank (only) Cycles Excessively
New mystery… While cruising down the interstate (and not braking) noticed only my secondary air tank cycles excessively.
Only the secondary drops from 130PSI to 120PSI then goes back up to 130psi, and repeats, every five or so minutes. Primary and aux tanks remain steady at 130psi.
All three tanks hold pretty steady when parked with engine off.
The bus passes the DOT brake test.
I replaced, as purely preventative maintenance, the Haldex air dryer almost one year ago and its integral governor cuts out at +/- 130psi
About 2 months ago, I replaced R12’s, R14, SR7 valve, PR4 shuttle valve, all brake chambers and hoses; and about two weeks ago, the secondary tanks check valve. I did blow into the check valve and it worked with human air pressure.
Hope someone might have an idea. Thank you, Jeff
-
6 Replies
-
Air suspension. This is normal and occurs on every one I have had. Leveling valves are working all the time when driving.
EDIT: My bad…I was thinking Aux tank not secondary brake tank. All 3 of my Prevost coaches would do that with the Aux tank.
-
I’m not sure about XL2 but XL1 the Primary and secondary tanks are only for brakes AUX tank and AUX system is for Suspension and other things, Do you have a AUX gauge? When I 1st bought 97 Royale the AUX gauge also follow’s the wet tank and driving using no brakes the AUX gauge went from 100 psi to 120 psi every 5 minutes that means at that psi the wet tank was doing the same. Mine was replacing old school dryer to a new Bendix AD9 dryer with a good check valve. Your secondary air tank in tied to AUX tank but check valve on secondary should prevent it from following AUX tank and there is a Pressure protection (75psi) on AUX tank right there. Maybe Pedal valve (treadle valve) is failing you also replaced parking brake valve ?? that’s tied to that system
-
What Art said. If only the secondary system is losing pressure and cycling it is most likely leaking at or before the service brake relay valve.
But if the aux system is losing air simultaneously it suggests an aux system leak.
The primary and secondary tanks are brake systems only and aux is anything but brakes unless someone got creative and modified the bus by using secondary air for something.
Unless the service brakes are applied there is no air pressure downstream from the relay valve, except the parking brake relay valve (in the rear) which has pressure to release the spring brakes for driving. Secondary is front only.
-
I wouldn’t really worry about it. Like art said the aux is the air suspension. I don’t watch my gauges but I’d assume this is normal and a pressure relief valve is going off. I hear mine do that sometimes when idling or parked
-
I don’t believe the Main and Secondary air gauges should move at.all when underway and off the brakes. Neither my 88 or 98 gauges moved while driving UNLESS there was a leak somewhere. Once, it was a brake air line that was rubbing against something and a hose needed replacement. When my gauges are moving I know repairs are on the horizon!
-
THANK YOU ALL for the replies
Have been on the road four straight days and late today finally arrived at our destination.
On day 3, the secondary tank stopped cycling excessively and held firm also throughout day 4.
Will be at our present campground for two weeks, then one day of travel, 12 more at another campground, then four days on the road heading back home.
Will see if it is truly resolved or re-occurs. THANK YOU AGAIN
Log in to reply.