in passage 68 will be connected to ps and the drive stroke will be initiated piston 34 and valve 36 positions at this time are shown in fig5 as piston 34 moves to the right on its own stroke edge a closes off edge 44 and edge b then uncovers edge 46 connecting pressure pv once again to pe and causing valve 36 to move again to the right as shown in fig4 the timing of this motion is such that edge d uncovers edge 54 just after piston 34 impacts anvil 38 and piston 34 begins a new cycle the energy of the impact against anvil 38 is transmitted into the shoulder of shank adapter 22 through the drill steel and bit 18 and into the rock fragments or other debris 16 which are causing bit 18 to be jammed this energy causes debris 16 to be broken up and dispersed thereby allowing bit 18 to be freely retracted from the drilled hole as long as bit 18 is encountering sufficient resistance to hold anvil 38 against face 56 piston 34 will continue its repetitive striking of anvil 38 however when bit 18 is freed and anvil 38 is driven back against face 58 by the upward force of piston 34 edge c again closes off edge 48 and edge b uncovers edge 42 this causes valve 36 to move back to the left as illustrated in fig3 maintaining pressure pd in passage 68 connected to ps and holding piston 34 in the rest position as shown in fig3 in contrast to the prior art the piston 34 of the reverse percussion device 30 is held upward against anvil 38 by supply pressure in the stalled condition.