assembly 12 having a relatively large irregularly shaped generally annular recessed portion or suction chamber 14 extending into the lower surface 16 thereof a discharge chamber 18 of frusto conical shape is also provided being defined by a radially inwardly inclined or beveled sidewall 20 extending between an upper surface 22 and lower surface 16 of valve plate assembly 12 a surface 24 of sidewall 20 provides a valve seat for a discharge valve member 26 which is urged in to sealing engagement therewith by gas pressure and a wave spring 28 extending between valve member 26 and a bridge like retainer 30 as shown discharge valve member 26 is of a size and shape relative to discharge chamber 18 so as to place a lower surface 32 thereof in substantially coplanar relationship to lower surface 16 of valve plate 12 wave spring 28 is located in a recess 36 provided in retainer 30 discharge valve member 26 is essentially pressure actuated and wave spring 28 is chosen primarily to provide stability and also an initial closing bias or preload to establish an initial seal other types of springs other than wave springs may of course be used for this purpose retainer 30 which also serves as a stop to.