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Air Dryer and other Pneumatic Information

Yahoo Message Number: 89705
Hi Folks,

The purge valve cycling was occurring every 30 seconds. Bendix, the maker of the AD-IP air dryer assembly, indicates this is the trigger point for troubleshooting the pneumatic system. Major tank leaks in 2003 came to mind (msg. 6746). A check with soapy water indicated no leaks in the right rear primary tank which connects to the suspension via a pressure protector, pack brake and aux leveling compressor, also check valves feed the left front primary tank and the right front secondary tank. The input from the dryer to the right rear primary tank also feeds the horn plenum thru a 70 psi pressure protector. It the tank pressure for some reason goes below 70 psi, the horn does not work.
There are only two air tanks in the system and are located up front but inside each is a partition so you get four tanks ? two primary and two secondary. There are 2 pneumatic diagrams ? D15993 and D15993B which reflect the moving of the two ride height valves from the front to the rear starting with Allure 30594 for the beginning of the 2001 model year in September 2000. During this transition, some of the old fittings were used, and as supplies were used up, new fittings were implemented per the B revision. So there were several transitional coaches built.
With the installation of 3 air gauges ? one on each of the tank drain valves (front driver's side), only the pressure in the right primary tank decreased from 125 psi to 78 psi. The secondary tanks and the left primary tank held at 125 psi after one hour. The long term leak rate was 5 psi in 20 hours which is well within the max. leak down rate of 3 psi per hour. This was a static test and when the IR ride height valves operate, I expect a much shorter cycling of the purge valve.
As done in 2007 in the first air dryer maintenance (msg. 34829), the assembly was removed from the coach. This time after removal of the canister, it was observed that the desiccant pellets had started to come apart and were migrating to all parts of the assembly base including the output internal check valve and the purge valve. After cleaning the base and installing a new purge valve, a new O-ring on the internal check valve and a refurbished air dryer canister assembly (torqued the 5/8 bolt to 70 ft-lb this time), and the remounting under the coach was completed. The purge valve did not operate for the 10 minutes monitoring period after the initial purge.
The part numbers are as follows. Purge valve assembly for the AD-IP dryer was 8000404 and Bendix has replaced it with a redesigned valve (has one new external housing with an added spring) part no. K022105. The air dryer canister part no. is 109493X which can be purchased from Rebuilders Enterprises, Inc (708 430 0030) for $75 (was $65 in 2007). Bendix indicates that coach air dryer replacement is every 3 years.
Second issue ? the governor cycling about every 40 to 120 seconds when under way. This has been mentioned in previous posts. CC did not engineer a large enough primary tank to solve this issue.
In the photos section, titled Added Primary Tank, shows an added tank which is connected to the right rear primary tank drain valve. The volume of this tank more than doubles the air volume. The pressure gauges have been left in place for leak down monitoring.

Fred Kovol

2000 Allure 30593