Patent GB-1396307-A (GB)
Title: Hydraulic percussive implement
IPC: F01L25/04
Filed: 1971-05-11
Abstract: 1396307 Hydraulically operated percussive tool AF HYDRAULICS Ltd 24 April 1972 [11 May 1971] 14212/71 Heading B4C An hydraulically actuated percussive tool comprises a reciprocable hammer piston 1 driven on an impact stroke by liquid supplied at high pressure to chamber 20 and on a return stroke by pressurized liquid in chamber 7 acting on area 15 of the piston when liquid supply to chamber 20 is interrupted or the liquid pressure is reduced. Should the piston overtravel on its working stroke its collar 9 will enter dash pot cavity 8 so that the liquid therein will cushion the piston. Casing 4 includes a holder (not shown) for a tool kit (not shown in Fig. 1), which tool bit is, in use, impacted by the piston. In the first embodiment (Fig. 1), conduit 18 is provided with a one-way valve 19 to facilitate return of the piston after overtravel. The chamber 7 may receive liquid at constant pressure from source 13 or may contain trapped liquid so as to form a liquid spring. In the second embodiment (Fig. 2) a high pressure liquid line 43 communicates constantly with chamber 7 via conduit 44 and chamber 20 communicates alternately with the high pressure line 43 and a lower pressure line 46 depending on the position of valve spool 37. The high pressure line 43 communicates directly with a chamber receiving a spigot 41 of the spool 37. The other end of the spool forms spigot 42, of large transverse area than spigot 41, received in a chamber which communicates via conduit 51 with an annular groove 52. The tool is illustrated in the condition when the piston is performing a working stroke. As soon as the piston head 2 passes groove 52 liquid, e.g. oil, trapped in conduit 51 and holding valve spool 37 to the right will be allowed to flow into chamber 24 so that the spool will move to the left under action of high pressure liquid acting on spigot 41. Chamber 20 will now be connected to low pressure line 46, and high pressure liquid in chamber 7 acting on shoulder 15 will move the piston on its return stroke. Liquid in chamber 24 will, on the return stroke, be exhausted via one way valve 26. At the end of the return stroke by-pass conduit 56 and groove 52 will communicate so that high pressure liquid from chamber 7 can act on spigot 42 to move the spool 37 back to the illustrated position. Dash pots 8, 54 are provided for terminating overtravel of the piston on the working stroke and each return stroke respectively, although dash pot 54 is not essential. Fig. 2 shows an ON-OFF valve 49 in its ON position to which it is depressed against spring bias by a pivoted trigger 50. An adjustable flow restrictor 67 may be provided in conduit 47, particularly if dash pot 54 is omitted. An accumulator may be provided in communication with high pressure line 43. The specification discloses alternative locations of valve 49 in the circuits controlling the valve spool 37, and the valve 49 may be combined with restrictor valve 67. Also, the valve spool 37 may be biased to the left by a spring rather than by high pressure liquid, as illustrated. In a third embodiment (Fig. 5, not shown) similar to the embodiment of Fig. 2, the conduit 56 is omitted and liquid trapped in dash pot 54 is forced to flow past enlargement 55 and, via a conduit (52), act on spigot 42 to force the valve spool to the right. The conduit (52) may be provided with a one way valve (65), and a restrictor valve (63). The lower dash pot of the third embodiment is similar to that of Fig. 2 with annular plate valve 19 and conduits 18 omitted and with a larger clearance between the collar and the wall of the recess.