but sufficiently above the vicinity of ports 30 as shown in fig1 the holes 37 are positioned above and away from ports 30 so as to prevent erosion of the holes 37 due to the swirl of fluid entering ports 30 thus drilling fluid is permitted to pass from throat 15 through holes 37 through annular space 28 through ports 30 and through orifices 54 into pockets 3 the strainer holes 37 are approximately 0 050 inch to 0 070 inch in diameter so as to be smaller than the apertures 40 thus foreign material large enough to clog orifices 54 cannot pass through strainer sleeve 26 when passing through throat 15 the annular space 28 is preferably made no wider than 0 070 inch so that it too prevents clogging of orifices 54 notice that the apertures 40 are sized to provide a flow rate through each of approximately 10 gpm to 15 gpm at the usual operating pressures in tests it has been found that flushing fluid exiting orifices 54 and passing through pockets 3 can cause erosion damage to the sealing surface of plungers 32 to prevent such erosion damage a clearance notch 50 is formed on the inner upper end of each wedge 29 as.