tively, a front elevational View, a side elevational view and a bottom plan view of the slide valve member; FIGS. l0 and ll are, respectively, a top plan view and a side elevational view of the retainer; FIG. l2 is a longitudinal vertical sectional View taken through another form of the invention; FIG. 13 is a sectional view taken substantially on line 13--13 of FIG. 12; and FIG. 14 is an enlarged