| 摘要 |
1356022 Percussive tools DOBSON PARK INDUSTRIES Ltd 21 Sept 1971 [10 Feb 1971] 4326/71 Heading B4C An impact tool including a hammer piston 11 incorporates a chamber 13 containing a compressible fluid (liquid or gas) and cylinder spaces 10a, 10b to which pressure fluid is supplied via a spool valve 21 to effect a piston return stroke. Return of the piston compresses the fluid in the chamber 13 and a high pressure in chamber 13 results in switching of the spool valve 21 to a condition permitting exhaust of the cylinder spaces. Thus the piston is driven on an impact stroke by the compressed fluid. As illustrated in Figs. 1 and 2 with the spool valve 21 in the exhaust condition and pilot valves 29, 30 in their illustrated conditions pressure fluid from line 32 is applied via valve 30 to the valve 21 while pilot valve 29 connects the valve 21 to exhaust via line 28, and the spool 22 is moved to a fluid supply position. When the high pressure in the chamber 13 is attained, on piston return, compressible fluid via lines 31 effects firstly movement of spool of valve 30 to connect the valve 21 via valve 30 to exhaust, and secondly movement of spool of valve 29 to connect the valve 21 via valve 29 to pressure fluid supply line 26. The spool 22 is now returned to its illustrated cylinder exhaust position, and the piston moves on an impact stroke. When the fluid in the chamber 13 reaches a low pressure the spools of the valves 29, 30 are returned to their illustrated positions and the cycle is repeated. Fluid is initially supplied via line 41 and check valve 40 to move the spool 22 to the illustrated position if the valve spool 22 is not in that position. The spring forces urging the spools of pilot valves 29, 30 to the illustrated positions are variable. A manually operable stop/start valve may be located in line 26 or line 32. In a modified tool (Fig. 3) the pressure fluid acting on the spool 22 to move it to the fluid supply position is cylinder exhaust fluid forced from the cylinder via a line 46a connected to the pilot valve 30 by a step on the piston entering a reduced cylinder space 10d. In this tool air is supplied via a one-way valve to space 10c and is compressed by the piston to a superatmospheric pressure to prevent ingress of air from the working area. In a modification of Fig. 3 (Fig. 4, not shown) the exhaust fluid forced via line 46a acts directly on one end of the spool 22.
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