Importance

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Abstract

A fluid-powered hammer drill has a bore in which a tool shaft is normally coaxially engaged. A piston displaceable in the bore defines a front return chamber of small effective piston surface area and a rear drive chamber of larger effective surface area. A passage permanently connects the front chamber with the high-pressure side of a pressure source. A reversible control valve is connected between both sides of the source and the rear chamber for alternately pressurizing and depressurizing same and thereby alternately displacing the piston axial forward to strike the rear end of the tool shaft and axially backward. A recoil-damping sleeve surrounds the piston axially ahead of the front chamber and has a front end axially forwardly engageable with the tool shaft in a frontmost position and a rear end defining with the bore a recoil chamber separate from the front return chamber. The housing is formed with a vent passage connected to the low-pressure side of the source and opening into the recoil chamber. This vent passage is uncovered by the sleeve for venting of the recoil chamber substantially only when the sleeve is in the frontmost position. The piston is formed with at least one bypass passage communicating for fluid flow between the recoil and front chambers when the piston is in or axially forward of its front position but blocked when the piston is axially backward of its front position.

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First Claim