Patent GB-1536494-A (GB)
Title: Pressure medium operable percussion tool
IPC: B25D9/12
Filed: 1976-03-04
Abstract: 1536494 Hydraulic reciprocating motors G KLEMM [trading as ING GUNTER KLEMM SPEZIALUNTERNEHMEN FUR BOHRTECHNIK 4 March 1976 [22 March 1975] 08778/76 Heading F1A [Also in Division B4] A pressure medium, constant energy percussion tool comprises a working cylinder 10, a working piston 11 reciprocable in the cylinder, a pressure fluid supply line 15, discharge line 21 and reservoir 43, a control valve 20 comprising a control member 55 reciprocable in a control cylinder between a first position (shown) in which pressure line 15 is connected to working cylinder 10 so that the piston 11 may make a working stroke and a second (upper) position in which discharge line 21 is connected to the working cylinder to allow a return stroke of the piston, a control line 24 connecting the working and control cylinders, a control surface 58 on control member 55 so that the control member is returned to its first position when a sufficient pressure is reached in control line 24, the tool being characterized by a control means 34 which effects the return of control member 55 to its first position only after the pressure in reservoir 43 has reached a predetermined threshold value, so as to give impacts of constant force irrespective of the delivery capacity of the pump. The pressure threshold is pre-selected to produce whatever impact force is desired. Preferably the pressure medium is a liquid and reservoir 43 contains liquid and gas. Pressure line 15 is permanently connected to lower portion 16 of working cylinder 10 so that a returning force is permanently applied to the lower face 17 of piston 11. The upper (annular) face 22 of piston 11 is larger than face 17 so that a working stroke is effected when pressure line 15 is connected to both upper and lower chambers 18, 16. Control line 24 is connected to working cylinder 10 via branch lines 25, 26, 27, 28, 65, 66, 67, some of which may be blocked with a plug, and associated annular grooves. During a working stroke control line 24 remains pressurized until piston portion 62 pauses below the first unblocked branch line 66. Control line 24 then drains via annular groove 69 and line 52. The decrease in pressure allows control sleeve 55 to be raised to thereby drain upper cylinder chamber 18 and so start the piston on its return stroke. The length of the working piston stroke is determined by the position of highest unplugged branch channel. The return stroke of the piston reconnects control line 24 via lower chamber 16 to pressure fluid reservoir 43 but the pressure does not act upon control surface 58 to move control sleeve 55 until the pressure is sufficient to open valve 34. In the embodiment of Fig. 2 (not shown) there is no valve 24 but the pressure in reservoir 43 and control line 24 has to reach a value sufficient to overcome a spring (35) which biases the control sleeve upward before the sleeve can be moved. The force of the spring may be adjusted by a set screw (36). The control surface and the top of the control sleeve may be combined to give a surface (582,) Fig. 3 (not shown) only slightly greater than the area of lower surface (572) so that only a weak spring (37) is required even for a high-pressure threshold.