GB1155191A - Crane safety device. - Google Patents

Abstract

1,155,191. Jib crane safety devices. G. W. SPARROW & SONS Ltd. 3 Oct., 1966 [14 July, 1965], No. 29932/65. Heading B8B. In a safety device for a jib crane the tension in the luffing line, due to the maximum load of the jib at maximum and minimum working angles is caused to exert the same pressure on a pressure-sensitive device. As shown, a main jib 2 is luffed about a pivot 4 by a multi-ply line 11 including reeved blocks running from one arm of a lever of a safety device 12 to an axis 5 for a secondary jib 3. The device 12 is mounted on the crane body 1 so that the underside of a second arm 20 of the lever is in contact with the operating button of an hydrostatic cell 30. The required shape of the lever of the safety device 12 is determined using a simulated lever by a method described with reference to Fig. 2. It is stated that a lever calibrated for a maximum jib length may be used when any shorter jib length is used and that the pressure sensed by the cell is substantially constant over the working range. The hydrostatic cell 30 is connected to an indicator device 32 with two ranges: one for " free duty " and one for " blocked " use. The secondary jib 3 is luffed by a line 8 connected to a lever arm 9 of a second safety device 10. (The lower part of the Figure shows an alternative position for the jib 2 with a different position for the device 10 and also an alternative length of jib 2<SP>1</SP>). Fig. 4 (not shown) illustrates a circuit for the indicator 32 wherein successive lamps under a scale over which a pointer moves indicate " safe," " maximum " and " over " load. An alarm is rung at "overload." The device 10 is also provided with an indicator 40 with successively illuminated lamps and an alarm. It is possible to lead the hydraulic pressure exerted by the two safety devices 10, 12 through a shuttle valve to a single indicating device, overload conditions either of the secondary jib or the crane as a whole being then indicated identically.