Abstract: An air distribution manifold assembly for air support convalescent beds includes a rectangular housing adapted to be secured to a flat surface of the bed structure and cooperating therewith to form an air chamber. A plurality of air distribution connectors extend from respective walls of the housing and are each provided with fixed orifice elements that define orifices of predetermined dimension for distribution of pressurized air to respective air cells of an air bed system. The housing structure defines an outlet opening having a plurality of closely spaced, side-by-side outlet ports that are controllably closed by a slide valve for controlling venting of pressurized air from the air chamber. The slide valve is electrically driven by a rack and pinion assembly and is selectively operable by the patient for adjusting the supply of pressurized air to the air cells to control the firmness of the air support bed.