Patent GB-884398-A (GB)
Title: Device for ground burrowing
IPC: E02F5/16
Filed: 1958-12-31
Abstract: 884,398. Ground burrowing. ZINKIEWICZ, W. Dec. 31, 1958 [Jan. 24, 1958], No. 42252/58. Class 85. In pneumatic apparatus, for ground burrowing, having an internal piston-hammer, the reciprocations of the piston are caused exclusively by the compressed air, and differences in air pressures at the two ends of the piston are used to move a valve which controls air admission to one end or the other. Fig. 1 shows diagrammatically the arrangement of air passages and ports. A sliding valve 19 moves across the chamber 10 to admit air to one or other end of the piston, and a valve 11 determines whether the piston blows are for forward burrowing or retraction in the burrow. As shown in Fig. 1, the apparatus is set for forward burrowing, the pressure air admitted at 4 having forced back the valve 11 against the spring 12 to open the passage 6 to the atmospheric vent 14 and to seal the passage 7 and ports 24, 25 therefrom. The piston 26 is about to be started on its return stroke by air from the passage 5 and port 21 entering the space 18. When the piston uncovers the port 22, the space 18 is connected to atmosphere, the pressure drops whilst the pressure of trapped air in the space 16 builds up to arrest the piston before it strikes the face 3<SP>1</SP>. The pressure differential on the sides of the valve 19 slides it over to open the passage 17 and close the passage 5, so that the piston begins its working stroke during which the port 23 is uncovered and the pressure in the space 16 falls whilst the trapped air pressure in front of the piston rises, when the port 22 is covered. The rise is insufficient to prevent the blow on the face 2<SP>1</SP>, but acts to return the valve 19 to its former position for a new cycle of operations. When the apparatus is to be retracted in the burrow, the pressure at 4 is reduced to allow the spring 12 to move the valve 11 to shut the passage 13 and to open the passage 7 to the atmosphere whilst sealing the passage 6 therefrom. The reduced air supply pressure is adequate to do the easier work of retardation. The backward action differs from the forward action only in that the position of the ports 24, 25 ensures that the piston blows are on the face 3<SP>1</SP> and the effective air-cushioning is between the piston and the face 2<SP>1</SP>. Fig. 3 shows the general shape of one embodiment of the invention. The piston 26 has a truncated conical striking end with air clearance 18 around it, and an aircushioning pocket 33 in the rear end. The valve 19 is a sliding sleeve valve with a centre diaphragm 8 to separate the operating pressure differentials. An attachment 20 for a rope is provided. The passage 5 and other passages, not shown, are formed by a cover 34 secured over a recess. The back end of the device may be enlarged, to open out the burrow as the device advances. The device may be arranged for curved burrows by inclining the axis of the nose 2 at a small angle to the axis of the main body, twisting of the device in the ground being prevented by a forwardly pointing blade on the nose, and a longitudinal fin on the main body. The device may have a non- circular section.