GB972929A - Telescopic lift ram for an industrial lift truck - Google Patents

Abstract

972,929. Ram for industrial lift trucks. YALE & TOWNE MANUFACTURING CO. July 26, 1963 [Aug. 10, 1962], No. 29660/63. Heading B8H. A telescopic lifting ram for an industrial lift truck has a small piston which is extended at a relatively fast speed before a larger piston is extended at a relatively slow speed. As shown, a small piston 13 slides in a larger piston 12 which slides within a cylinder 11. A piston head 23 of the larger piston has a check valve 37 for controlling flow of fluid from an end member 14 of the cylinder 11 into the large piston 12. A spring-pressed check valve 31 may be operated by a part 33 of the smaller piston 13. Assuming that the valve 31 is closed and that fluid is locked in an annular space 22 between the cylinder 11 and the larger piston 12, Fig. 1, piston 12 cannot extend when pressure is applied through a passage 17 in the end member 14 but the smaller piston 13 is extended at a relatively fast speed. At full extension, Fig. 2, the check valve 31 has been opened and fluid moves from the space 22 to the passage 17. Movement of fluid from the space 22 allows the larger piston 12 to extend and valve 37 is closed as a pin 39 of the valve 37 moves away from a surface 40. The smaller piston 13 is thus locked while the larger piston 12 extends relatively slowly. If the lifting pressure is allowed to discharge through the passage 17 by operation of a valve 20, the larger piston 12 retracts while piston 13 remains locked and extended. When the larger piston is fully retracted, valve 37 is opened due to contact with the surface 40 and the smaller piston retracts at its faster speed. The check valve 31 is closed by retraction of the smaller piston, thus locking the larger piston in fully retracted position preparatory to the next lifting operation.