The air governor on the compressor controls the purge function of the air dryer. It tells the air dryer to open it's purge valve when pressure reaches the governors cut-out point, and the purge valve is held open until the governor reaches it's cut in point at which time it tells the air dryer to close the purge valve. There is a one-way check valve at the output of the air dryer to the wet tank which locks air into the bus's system so that no air should escape while the purge valve is left open. The air governor acts like a control switch for the air dryer, the air dryer just does what it's told to.
An air leak of 10 lbs per hour is well within DOT specifications. I'm not sure exactly what your problem is, maybe you could re-state what you are worried about. Also, is your coach air suspension? What uses air other than brakes?
Brian
