| 摘要 |
The legs of the landing gear of a semi-trailer may be automatically extended and retracted by a pneumatically operated actuator adapted to be connected to the crankshaft of the landing gear and adapted to rotate the cross-shaft of the landing gear selectively in either direction at a high or low speed. The crankshaft is rotated by gears and ratchets which are driven by pawls adapted to be reciprocated by an air-actuated cylinder and adapted to be alternately positioned in active and inactive positions. The flow of pressurized air to the cylinder is controlled by a cycle valve and an on-off valve, the latter being capable of turning off the actuator automatically when the legs are fully retracted.
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