Last week 2 buses would not build air pressure above 30psi when the buses were started in the morning. I let the buses run until they were at operating temperature and then pumped the brakes down to zero a few times and then they built normal pressure. We have had this problem before with other buses in past years when the temperature at night drops below 30. We would replace the purge valve on the air dryer or the governor on the compressor and that would solve the problem. Did that to both buses and they still won't build air passed 30 psi. One bus is a 2003 Blue Bird with a Cummins engine, and the other is a 2008 International. Any ideas?
It could be the check valve sticking between the wet tank and the other tanks. I have had that happen before one or neither of thanks won't build pump them down and will hear a pop and they start filling, especially after they have sat.
Had a similiar issue with a Bendix AD-9 dryer not always building up air. Driver was making several stops in a short distance and the compressor could not keep up with demand. We tried to duplicate this in the shop and could not do it. Replaced the govenor to no avail since the dryer was working correctly. Well long story short the "O" ring between the AD-9 bottom half and the top "CAN" had an air leak. Hard to hear air leaving shile the bus was running. Air is in all parts of the dryer while the compressor is pumping air till the govenor kicks out and dumps the air in the dryer via the dump valve. Then the air in the desicant cartridge leaves out the bottom end. There is also a small hole on top of the cartridge that allows the remaining air in the dryer to slowly escape until the next pumping cycle begins. (The dump valve should stay open on and AD-9 till the govenor kicks in)
Also if your dryer has a heater element in it, make sure it is working correctly. you can find out how to do this by going to Bendix web site or do a google search.
Dont know if this helps but it was a learning expierence.