Control arrangement for the forward and backward movement of percussive boring rams

Claim 1

In a self-propelled, pneumatically operated, percussive boring ram of the kind comprising a hollow housing, a chisel mounted at the boring end of said hollow housing, a percussion piston reciprocably mounted in said hollow housing, a back stop in said housing for limiting rearward movement of said percussion piston in said housing, said chisel forming a front stop for limiting forward movement of said percussion piston in said housing, means defining a cylindrical chamber in said percussion piston, a tubular valve member having a piston head and located in said housing with said piston head received in said cylindrical chamber, said tubular valve member being adapted to admit compressed air into said cylindrical chamber for reciprocating said percussion piston and thereby dRiving said boring ram, and means whereby said tubular valve member can be adjusted between two operative axial positions relative to said housing to determine whether said percussion piston acts to drive said boring ram forwards or backwards, the improvement wherein said boring ram includes a guide member attached in said housing and said tubular valve member extends through said guide member, and means for locking said tubular valve member in either of said two operative positions during operation of said boring ram, said locking means comprising axially inter-engaging stops on said tubular valve member and on said guide member, and a releasable catch which, when engaged, prevents rotation of said tubular valve member relative to said guide member, said stops being arranged whereby, on release of said catch, said tubular valve member can be rotated into a position in which said stops are misaligned and allow said tubular valve member to be moved axially from one of said operative positions to the other.