| 摘要 |
There is disclosed an impact applying mechanism, particularly as applied in a subterranean drilling apparatus, and comprising a cylinder (13) arranged with its axis substantially vertical and connected to the member to which impact is to be applied, a piston (5) slidably mounted within the cylinder (13), means to admit pressure fluid to the cylinder (13) below the piston (5), at least one valve tube (24), slidably mounted in the base of the cylinder (13), coil springs (30) to bias the upper end of the valve tubes (24) into sealing engagement with the underside of the piston (5) when the piston is in its lowest position, a flange (26) on the upper end of the valve tubes (24) upon which fluid pressure in the cylinder (13) acts to produce a force urging the end of the valve tubes (24) into contact with the underside of the piston (5), and further coil springs (32) to provide a force to said valve tubes (24) of a magnitude which increases as the piston (5) moves upwardly relative to the cylinder (13) to subsequently urge the ends of the valve tubes (24) out of contact with the underside of the piston (5). Nuts (28) are also provided to enable the force exerted by the further coil springs (32) to be adjusted to vary the stroke of the piston (5) by varying the point at which the seal between the valve tubes (24) and the underside of the piston (5) is broken and the pressure is released from the cylinder (13) through the valve tubes (24
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