[Tim]

The valves on this unit only show Prevost numbers and that is why I needed confirmation to cross over, for 58 bucks, there is no point in me rebuilding them but will build a spare or 2. As far as getting under the bus without jacking and blocking….that’s for skinny guys….not me! I drove it up on some ten inch timbers and blocked the body also, something to watch is overjacking the body as this can lead to an airbag blowout.

[Mike]

In the picture above in this post there are two valves shown. The one on the right is the Norgren valve. The one on the left is a Burkett valve. Burketts were valves that Prevost used in the mid to late 90s as a replacement for the Norgren three way valves. They come either NO or NC and they cannot be altered. The first versions of the valves did not have a return spring in them and we had numerous issues where the valve would stay in the midway position. This led to air systems not building air correctly. Normally the bad valve was on the tag lift system and by simply cycling the system you could get the valve to seat itself and the air would build correctly. Burkett came out with a valve with a return spring ( the new Burkett valve) but we went back to Norgren valves eventually. Another issue with the Burkett valves was they were made for a much cleaner, industrial application. The coach pneumatic system in not a completely clean and dry environment. The Burketts did not fair well on the coach. The Norgrens were more robust and did not mind a little oil and water in their working environment.

Most of the people in Prevost service do not know anything about the Norgren numbers. Prevost parts secures the correct Norgren number for the application from the engineering department and then a Prevost part number is generated. To get the Norgren number we would have to get someone in parts to look at the cross reference file for the correct Norgren number. That is why you may get a blank stare from a tech if you come out with a Norgren part number.

As noted also above the type of valve you need (NO or NC) will be dependent upon your pneumatic configuration in the rear of the coach. Up through 1996-1997 the plumbing of the tag axle lift circuit required that there be sufficient air pressure in the auxilary air tank air sytem to properly pilot the valves associated with the tag axle and tag lift system. Thus you needed good aux. air pressure to keep the coach at normal ride height in the rear of the vehicle. Lack of proper air through an air leak would eventually reduce pilot or control port air pressure to the point where the internal spring tension of the valve overcame the control pressure and the system cycled much the same as if you had flipped the tag lift lever. The difference being that there is no aux air pressure left to do anything with the system.

Engineering at Prevost redid the pneumatic “plumbing” of this circuit in 1997 so that there were no control pressures to any of these valves to keep the tag axle down and the tag lift circuits off. There was a maintenance bulletin released “Service Bulletin 96-14B) to increase the reliability of the pneumatic system. The bulletin can be found at https://secure5.volvo.com/technicalpublications/pdf/SB96-14B/pdf. There were various kits made at the time for different models. These would come with instructions and valves that had the proper brass fitting for the application. The kits also included an inversion valve that had to be plumbed into the circuit. Prevost has always cancelled the brake boosters on the tag axle when it was lifted to prevent tire damage. As we were changing the way the axle was controlled we had to change the control of the Bendix R12 valves that controlled whether there would be brake application pressure sent to the boosters on the tag axle or not.

The modification takes some time as the old valves need to be removed and air lines properly identified. Then the new valve installed correctly and the inversion valve installed. Plus the light circuit in the dash had to be changed to reflect the lack of air pressure in the controls when the vehicle was in the normal ride height position.

All that being said: to check your system! Run vehicle and get all air tanks filled. Turn off coach. Open accessory (auxilary) air tank and bleed down the pressure. If the coach has the newer system installed the vehicle should NOT settle in the rear as if you flipped the tag lift lever. If if does squat, then it most likely did not have this modification done.

A bit lengthy but I hope that it helps with the pneumatic valves and systems.

[Walter]

Thank You! That’s an incredible fountain of information. Lot’s for me to work with there. cheers!

[Fred F.]

Prevost
Service, Thank you for being there for us. Just another reason to love
the Prevost chassis. All of us, I am
sure, appreciate you monitoring this site and answering our questions.

Thank
you again for being there to help us.

Fred

[Doug]

My pleasure! Happy Motorhoming to you all!