Improvements in and relating to pit props

摘要

747,266. Pit props. GUTEHOFFNUNGSHUTTE STERKRADE AKT.-GES., [formerly GUTEHOFFNUNGSHUTTE OBERHAUSEN AKT.-GES.]. June 17, 1953 [March 2, 1953], No. 16747/53. Class 20(2). A telescopic pit prop has energy storing means which is energised when the prop telescopes under load, the energy-storing means being prevented, by a releasable locking device, from parting entirely with its energy during the dismantling of the prop. In one form the inner prop member 2, Fig. 1, has a cylinder 10 at its lower end engaging over a base plunger 8, and at its upper end a piston 6 engaging within a cylinder 5 carried by the outer prop part 1. The prop parts may be frictionally gripped by a clamp actuated by a lever 3. With the prop parts clamped together and the prop in operative position, subsidence of the roof compresses the air in the cylinder 10, a detent 11 wiping over a stop on the plunger 8. Dismantling is effected by actuation of the clamp lever 3 to release the clamp, whereupon the prop member 2 rises under the high pressure in the cylinder 10, to compress air in the cylinder 5, to a low pressure. Shock occurring at the arrest of upward movement by interaction of the detent 11 and stop, jumps the base 12 free of debris and allows the prop to be withdrawn by an attached rope. The clamp is reapplied immediately after the base has jumped in order to retain the air at low pressure in the cylinder 5. When the prop is repositioned, the clamp is released to allow the low pressure air in cylinder 5 to move the prop head 14 into contact with the roof, whereupon the clamp is reapplied and detent 11 disengaged to allow the high pressure air in cylinder 10 to apply initial loading to the roof. The prop head 14 may be adjusted by a wedge 13. The prop head and/or base 12 may be resiliently connected to their respective prop members e.g. as shown by Fig. 2, a pawl 16 retaining the head or base in pre-loaded condition. Springs or rubber buffers may be employed as the resilient members, and the cylinder and plunger devices at the prop ends may be replaced by chambers 5 or 10 having corrugated walls which are expansible under pressure. The energy storing device may alternatively be provided in a separate base which may be removed from the prop and associated with any other prop. In another embodiment, the prop is spring loaded, Fig. 4 and clamped by a wedge 28 controlled by a wedge 34, which may be retained in inoperative position, by a catch 32 and interengaging stop 29, against spring pressure 30. The subsidence of the roof compresses the spring 20, the energy being retained by interengagement of the stop 24 and detent 16.