| 摘要 |
A self-propelled pneumatically operated percussion boring apparatus for boring holes in the ground of the kind which includes a percussion piston which is reciprocated pneumatically in a tubular housing is provided with a control device for causing the apparatus to make either a forward movement or a return movement. The control device comprises a control sleeve which has air ports through its wall and over which a skirt of the piston passes as, in operation, the piston reciprocates. The skirt has ports which come into register with ports in the sleeve and the sleeve is fixed in position in the housing and has a control tube rotatably mounted within it. The control tube has one or more ports through its wall and compressd air for operating the apparatus is supplied through the control tube. The control tube is set in either one of two positions, in one of which the port or ports in the control tube are out of register with a port or ports in the sleeve and this causes the apparatus to move in one direction and in the second position the port or ports in the control tube are in register with the port or ports in the sleeve and this causes the apparatus to move in an opposite direction.
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