GB1278127A - Improvements relating to percussion tools - Google Patents

Abstract

1278127 Percussive tools MISSION MFG CO 9 July 1969 [15 Aug 1968] 34670/69 Heading B4C [Also in Division E1] In a down-the-hole percussive drill having a casing 5, a hammer piston 32 and an anvil bit member 13 slidable in the casing between a working position and a fully extended position (shown), ducting for exhausting the forward working chamber 53 when the member is in the fully extended position is closed in the working position of the member. The construction prevents working fluid (gas) leaking into the chamber when the member is fully extended causing continued operation of the drill. When the member is fully extended the bulk of the working fluid flows into the hole through passages 52, 36, 39 whilst the leaking working fluid passes from the chamber through flutes 37 in the member 13, through annular groove 41 in the casing, between splines 40 in the casing, and through passages 35 in the member to combine with the working fluid in the passage 36. In the working position the member abuts the bottom of the casing and the connection between the passages between the flutes 37 and the groove 41 is blocked to prevent flow through the duct. In a modification the passages 35 are replaced by openings in the casing. In another modification the passages 35 are dispensed with and the splines and splineways 28, 29 of the member are extended and have sufficient clearance with the matching splines 40 and splineways of the casing to form discharge passages for the leakage fluid. In a further modification one of the splines on the member is dispensed with to form a discharge passage.