| 摘要 |
A drop hammer has a hydraulic cylinder and piston assembly with a hammer weight attached to the piston and a sleeve valve at the lower end of the cylinder coaxial with the cylinder. An outer casing surrounds the cylinder, forming an annular passage from the valve to the upper end of the cylinder. Through servo control means that may be automatically operated by the hammer movement, the valve alternately admits pressure to the cylinder space below the piston to raise the weight, and opens said cylinder space to the annular passage to put both ends of the cylinder in communication and allow the hammer weight to fall.
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