| 摘要 |
A pneumatic percussion machine such as a drill having a piston reciprocating in a casing, chambers formed in the casing at or towards the ends of the piston, the arrangement permitting compressed air to be supplied alternatively to the chambers, the compressed air to the one chamber being supplied through a projecting member located co-axially in the casing, and over which the piston reciprocates, and the piston and compressed air from the other chamber being exhausted from such chamber between the wall of the casing and a stepped portion of the piston and then through the piston to atmosphere. Provision is made for the piston to move to a position, in an inoperative condition of the machine, in which both chambers are open to the atmosphere. |
