Bleeding air tanksby Tom Jones
Diesel coaches rely on compressed air for brakes, suspension and, in some cases, automatic leveling. The air system will include a compressor, air dryer and several air tanks. Although the dryer will effectively remove moisture from the output of the compressor, it's possible for moisture to accumulate in the tanks, especially after a period of storage. Therefore, it's necessary to periodically bleed the air tanks to remove any accumulated moisture.
Some coaches employ automatic air ejectors or "spitters" that literally spit moisture (often heated) out under pressue. However, they do not necessarily remove all the moisture and additional manual bleeding will be required.
Air tanks incorporate manual bleed valves which are used to expel moisture. On some coaches this requires crawling under the coach to open the valves, whereas other coaches have lanyards attached to the valves, allowing them to be operated without crawling under the coach. Many owners have reported that the lanyards were coiled up adjacent to the valves, requiring them to uncoil and route the lanyards prior to first use.
The procedure for bleeding varies a little between manufacturers, but it essentially requires a bleed valve to be opened long enough to expel all the air and moisture. It's usually necessary to expel all the air because the air rushing out would push aside any moisture.
The required frequency of air bleeding varies by manufacturer and can be anything between daily and every months.