| 摘要 |
A hydraulic impact device in which a hammer member having a piston portion is reciprocally disposed in a cylinder, a reciprocating sleeve valve is disposed within the cylinder and surrounds the hammer member. The sleeve valve has a first peripheral seal with an upper portion of the cylinder and a second peripheral seal with the lower portion of the cylinder so that an annular cavity is formed between the first and the second peripheral seals. The bottom portion of the sleeve valve forms a single seal with the upper portion of the piston section. A pressure relief valve is situated between the inlet to said annular cavity and an annular cavity below the piston portion to insure that the pressure in said annular cavity is greater than the pressure in the cavity below the piston portion and the sleeve valve thus effecting a sealing force between the sleeve valve and the upper face of the piston portion. An energy storage means is provided for receiving energy from said ram member during its upward stroke. The upper and lower sealing portions of said sleeve valve are axially spaced such that when said lower sealing portion seals a fluid inlet port, the upper sealing portion opens a fluid outlet port thereby reducing the pressure in said annular cavity by interrupting a fluid communication between the inlet port and said annular cavity and establishing fluid communication between the outlet port and said annular cavity.
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