| 摘要 |
A fluid operated ram comprises a striker body guided in an upright housing between an active stroke and a return stroke and striking at the end of its active stroke an impact transmitter resting on a member to be driven into the ground by the ram. The striker body is connected by a piston rod to a working piston reciprocatedly arranged in a cylinder coaxially mounted on the upper end of the housing, so that the striker body is driven during reciprocation of the working piston. The working piston is a differential piston and divides the cylinder into a first chamber above the upper larger face of the working piston and a second chamber below the smaller annular face of the differential piston. The second chamber permanently communicates with a source of pressure fluid, while control elements, including an axially movable valve slide and a valve rod cooperating therewith, serve to alternately connect the first chamber to the source of pressure fluid or a tank in dependence on the position of the striker body in the housing. The length of the valve rod is dimensioned so that the lower end thereof engages a contact face on the working piston during the downward movement of the latter together with the striker body, but is disengaged from the contact face shortly before the striker body hits the impact transmitter so that the resulting blow is not transmitted to the valve rod and the other control elements.
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