Patent GB-1041641-A (GB)
Title: Improvements relating to grabs
Inventor: STEPHENS JOHN ESKETT
IPC: B66C1/54
Filed: 1964-01-21
Abstract: 1,041,641. Devices for engaging and lifting articles. FAIREY ENGINEERING Ltd. Feb. 3, 1965 [Jan. 21, 1964], No. 2650/64. Heading B8H. A grab for use with the refuelling machine of a nuclear reactor comprises jaws 13, Fig. 2, for engagement externally or internally with an object such as a seal plug, a fuel element, a debris can or can lid or a tubular adaptor for a fuel element pencil and includes a sensing device in the form of a plunger 16 which when it is moved by engagement with the object operates switches 32 to send a signal to the grab operator indicating that the grab has reached a position in which the jaws are capable of engaging the object. The grab body is in two parts 11A, 11B, Fig. 1 (not shown), the upper part 11A housing a solenoid 12 for operating the jaws 13 which are three in number and are located in the part 11B. The part 11A also houses a spragging device 14 for engaging the inside of a member such as a reactor standpipe or the charging tube of the refuelling machine in the event of a failure of the suspension cable or of the hoist of the refuelling machine. The solenoid plunger rod 15 carries a disc 19 to which the jaws 13 are connected by push-rods 20 and links 21, the jaws 13 being pivoted on pins 18 and the plunger 15 being urged downwardly to place the jaws 13 in the disengaged position by a spring 15A. Energization of the solenoid 12 moves the jaws 13 to their engaged position against the spring 15A. The plunger 16 has three arms 39, each arm having an aperture containing an annular or semi-annular magnet 41 through which extends one of the switches 32. Each of the latter comprises a glass tube 34, Fig. 4 (not shown), disposed within a metal sheath 35 and containing co-operating trembler contacts 37 which close when acted upon by the associated magnet 41 to complete an indicating circuit; each switch 32 is adjustably mounted in the body part 11B. The plunger 16 is lightly urged to its lowest position by springs 48, 49. Three pivoted bell-crank levers 55 are provided for locking the jaws 13 in their engaged position, each lever 55 having one arm 57A engaged with an adjustable spring-loaded plunger 60 and the other arm 56 disposed to snap-engage a step or recess 53 in the disc 19 when the latter is moved upwardly to move the jaws 13 to their engaged position. The arm 56 is disengaged from the step or recess 53 by further movement of the plunger 16 upwardly from its object-proximity level, e.g. by lowering an engaged object into a support surface, to permit the spring 15A to move the jaws 13 to their disengaged position. Switches 72 are provided which are similar to switches 32 and indicate when the arms 56 engage the steps or recesses 53. In an emergency the levers 55 may be moved to disengage the arms 56 from the steps or recesses 53 by a ring 90 which can be pushed downwardly, e.g. by the motor-driven pawl release mechanism of the bridging tube of the refuelling machine, on to levers 92 pivoted to the disc 19 and engaged with heads 62 of the plungers 60. Further switches 80, Fig. 6 (not shown), similar to the switches 32 and 72 are associated with the disc 19 to indicate when the emergency release mechanism has operated.