Patent GB-1392868-A (GB)
Title: Pneumatic burrowing apparatus
IPC: E21B4/14
Filed: 1972-11-20
Abstract: 1392868 Boring earth &c P SCHMIDT [trading as TRACTOTECHNIK PAUL SCHMIDT] 20 Nov 1972 [18 Nov 1971] 53539/72 Heading E1F A pneumatically-operated, self-propelled burrowing apparatus for driving or enlarging holes in earth, comprises a tubular housing 1, a percussion piston 16 movable axially to and fro in the housing, and a striker-tip 8 arranged to slide axially relative to the housing and bearing against the housing in the working direction via adjustably prestressed resilient means 3. The piston 16 strikes the striker-tip 8 via an intermediate piston 15 which is mounted between resilient buffers 18. Compressed air enters the borer through the bore 39 of a control sleeve 35 and acts on a hollowed rear portion of the piston 16 to accelerate the piston towards the intermediate piston 15. During this forward movement of the piston 16 'the air in front of the piston escapes to atmosphere between the piston 16 and housing 1, and via a bore 41 in the piston 16 and bores 43 in a collar 36 of the control sleeve 35. During the piston's travel forwards the bore 41 is shut-off from the atmosphere by the front portion of the control sleeve 35, and is subsequently brought into communication with the incoming compressed air in the bore 39. The resulting build-up in pressure at the front of the piston 16 returns the piston to its starting position following impact with the intermediate piston 15. In an alternative embodiment, figs 3-6 (not shown), the control sleeve (135) is mounted slidably in the axial direction in the housing between two limit positions, in one limit position the movement of the housing is forwards, and in the other position (the control sleeve position being changed by pulling on a drag rope (69), the movement of the housing reverses, for withdrawal of the apparatus. The compressed-air supply line is protected by a tube 44 of synthetic material clamped to the rear of the housing 1. The striker-tip which is shown to be conical may alternatively take the form of a gouge (62), fig 2 (not shown), and be additionally provided with a tapered detachable ring (68) for enlarging the borehole. The housing may be provided on its outer surface with transverse grooves, or, for the purpose of guiding the borer along curved paths, with curved guides (128), fig 12 (not shown), or adjustable guides (127), fig 11 (not shown). The guides may alternatively be provided on a stiff curved protective tube (not shown) surrounding the housing 1. For the purpose of boring a second parallel hole the borer may have attached in parallel thereto a guide body (125), fig 10 (not shown), which in use is advanced along the first borehole. A universallymounted device (75), fig 7 (not shown), for aligning and introducing the borer into the earth is provided with jaws (76, 77), mounted on spring-loaded parallel levers (78, 79), the jaws being arranged to open during each movement of the borer in the working direction and to close and resist movement in the opposite direction. Inclination of the borer may be set by a device (122), fig 9 (not shown), employing a plumb-bob.