Pneumatic reciprocating mechanism

In a pneumatic impact mechanism, comprising a working member (11) reciprocably guided in a housing (10) and balanced between a spring (32) and a pressure air supplied working chamber (49);

• the working chamber (49) being defined by a rear end portion (29) of the working member (11), a reaction support member (12) and an elastic seal element (47) located between the working member (11) and the reaction support member (12),
• the improvement wherein:
• the seal element (47) comprises an annular axially extending valve collar (48) which is radially expandible by the air pressure in the working chamber (49) to an outer diameter exceeding its nominal outer diameter;
• the reaction support member (12) comprises a depression (51) located coaxially with said radially expandible valve collar (48), said depression (51) having an inner peripheral wall (52) of a diameter exceeding the nominal outer diameter of said radially expandible valve collar (48);
• said radially expandible valve collar (48) during each reciprocation cycle of the working member (11) entering said depression (51) and by radial expansion therein establishing an air tight seal with said peripheral wall (52) of said depression (51);
• said housing (10) having a pressure air supply passage (39) therein, said pressure air supply passage being in communication with said depression (51) in said reaction support member (12), said depression and said seal element (47) with said radially expandible valve collar (48) at least partly defining said working chamber (49);
• a feed valve (55) in communication with said pressure air supply passage (39) for selectively closing off said pressure air supply passage to the pressure air when said seal element (47) and said reaction support member (12) separate to such an extent that the seal between said radially expandible valve collar (48) and said peripheral wall (52) of said depression (51) is broken, thereby reducing air consumption of said impact mechanism;
• said pressure air supply passage (39) comprising an elongated hollow element (37) having its hollow portion in communication with said depression (51), said elongated hollow member (37) having openings (54) therein for receiving pressure air from a pressure air source and for coupling said received pressure air to said working chamber (49);
• and
• said feed valve comprising a valve element (55) slidably mounted within said elongated hollow member (37) and being movable relative thereto, said valve member (55) being movable within said elongated hollow member (37) to block said openings (54) when said seal element (47) and said reaction support member (12) separate to such an extent that the seal between said radially expandible valve collar (48) and said peripheral wall (52) of said depression (51) is broken.