Patent GB-398133-A (GB)
Title: Improvements in and relating to elevating trucks
IPC: B62B3/06
Filed: 1933-05-10
Abstract: 398,133. Hand-trucks ; dashpots. LEWIS-SHEPARD CO., 125, Walnut Street, Watertown, Massachusetts, U.S.A. May 10, 1933, No. 13575. Convention date, May 16, 1932. [Classes 108 (i) and 108 (iii).] A hand-truck with an elevating load platform is arranged so that the load platform is elevated by an upward and rearward motion obtained by a thrust member operated by the steering tongue, and is adapted to be locked at its elevated position, a dashpot being provided in which the level of the operating fluid is maintained and in which the speed of descent is substantially constant for all loads. The load platform 23, 24 is connected to the main frame 1, 2 by pairs of links 31, 37, 38 and is provided with a transverse member 28 on which is positioned a thrust block 44 having a rounded face 46. A steering tongue 14, 15 is pivoted at 18 to the steering post mounted in the front headstock of the main frame and has pivoted thereto, below the pivot 18, a thrust member 19 which is positioned by a spring 21 to encounter the thrust block 44 when the steering tongue 14, 15 is depressed causing the load platform to be thrust rearwardly and thereby elevated. A gravity pawl 48 is provided with a shoulder 51 adapted to engage a rotary shaft 49 to lock the load platform in its elevated position, a pedal 53 being provided to rotate the shaft 49 to disengage the locking pawl 48 when desired. The dashpot, which is inclined, is provided with a reservoir at the end of the cylinder, the bottom 65 of the reservoir and preferably its longitudinal axis being horizontal when the load platform is in its lowermost position. The reservoir ensures that the cylinder below the piston at least is full of the operating fluid. The piston 61, Fig. 5, is provided with a plug 71 to which the piston-rod 62 is secured and in which apertures 72 are provided, similar apertures 74 being provided in a plug 73 on the other end of the piston to allow unimpeded elevation of the load platform. A plug 76 having restricted apertures 78 communicating with an annular chamber 79 in communication with an axial bore 81 is screwed into the plug 73 and a stem 82 having an axial bore 83 and radial ports 84 is also connected to the plug 73. A sleeve valve 86, with a skirt 87 bearing on a collar 85, slides on the stem 82 and is provided with a port 89. Another sleeve 90 with a port 93 slides on the stem 82 and a cap 95 having radial ports 96 is provided together with a spring 97. Under light load the fluid which is prevented from passing to the top of the piston through the ports 74 by the check valve 75 passes through ports 78, axial bores 81, 83, and ports 84, 93, 96 to the interior of the piston and thence through the ports 72. Under heavy load the rush of the fluid into annular chamber 92 causes a pressure to be built up in annular chamber 88 by way of port 89 which pressure forces the sleeve valve 86 to the right against the action of the spring 97 partially covering the radial ports 84 and so restricts the flow of'the operating fluid. The strength of the spring is so chosen that the restriction of the ports 84 and consequently the resistance to the passage of the fluid is such that a resistance is offered substantially proportional to the weight of the load so that the load platform will descend at the same rate of speed irrespective of the load.