Relay valve for tractor trailer brake systems

Claim 1

In a relay valve comprising a housing having an exhaust opening at its upper end, a partition in the housing dividing a lower supply chamber having supply means from an upper delivery chamber having an outlet means, the partition having a circular opening with a seat thereabout, a dual valve spool disposed axially in the housing and mounting a pair of spaced upwardly facing gaskets, one above the other, the lower gasket adapted to engage the seat, means biasing the spool upward into such engagement, a diaphragm in the housing and parallel to and above the partition and defining a control chamber in the housng thereabove, the diaphragm having a central opening closed by an upwardly extending open tube, the lower end of the tube having an exhaust seat adapted to engage the upper gasket of the spool and the upper end of the tube slideably and sealingly engaging in the exhaust opening of the housing; the improvement of the dual valve spool having a central axial cylindrical opening and a depending annular surface approximately the same diameter as the exhaust seat, a rigid shaft of equilateral polygonal cross section fixedly secured to and extending upward from the lower end of the housing, the shaft and the cylindrical opening having approximately the same major cross-sectional dimension, an annular flange surrounding the shaft and extending upward from the lower end of the housing, the flange telescopingly and sealingly engaging said depending surface to form a closed chamber, the shaft slideably penetrating the dual valve spool by its axial opening to guide precisely the vertical reciprocation of the dual valve spool and to communicate ambient air from the exhaust opening to the closed chamber to balance pressures on opposite ends of the spool within the diameter and to thereby improve control characteristics.