GB382122A - Improvements in or relating to hydraulic jacks - Google Patents

Abstract

382,122. Lifting-jacks. PFAUSER, E. M., 726, Lefeber Avenue, Wauwatosa, Wisconsin, U.S.A. Dec. 12, 1931, No. 34535. [Class 78 (iii).] In a hydraulic jack, wherein the pump piston forms a plurality of working chambers, means are provided for automatically bye-passing the fluid from one of the chambers to reduce the operative capacity of the pump when the ram encounters a predetermined load. As shown in Fig. 7, the piston 15, operating in a well 37, is provided with a recess 44 which terminates in a bore 45 engaging a stem 39 screwed into the casing 16 at 40 and provided with a bore 41 communicating with inlet and outlet passages 50, 56, respectively. When the piston is moved upwards by reciprocating a tubular handle 8, Fig. 2, connected thereto by a yoke 7 and links 21, 22, 25, oil is drawn through ports 49, 51, Fig. 7, from the reservoir 54 into the well 37 and bore 45, and on downward movement of the piston is forced out through ports 49a, 51a, to a chamber 57 to operate the ram 14, Fig. 2, and raise a pivoted lifting arm 9 supporting a crutch 10. When a predetermined load is encountered by the ram, a spring-loaded valve 60 is opened and oil from the well 37 is byepassed through a channel 59 to the reservoir 54. The arm 9 is lowered by opening a release valve 26 connected, by a universal coupling and rod 28, to a rotatable grip on the handle 8. The jack is supported by pairs of rollers 4, 6. In a modification Figs. 3 and 4, the handle 8 is adjustably mounted with respect to the pump by means of a spring-controlled pin 33 which is operable by a trigger 36 and engages one of the recesses 32 in a detent 31, pivotally mounted on a shaft 5a and connected to the pump by the link 25 as above.