Support prop

Abstract

A support prop which includes a cylindrical aluminium liner which is externally reinforced with a shell made from a composite material, an aluminium plunger with a seal which engages with an inner surface of the liner, a filler valve through which a volume inside the liner, adjacent the seal, in use is pressurized with a fluid, and a pressure relief valve which in use allows fluid under pressure to escape from the volume as the plunger is forced into the liner.

1 . A support prop, comprising: an elongate cylindrical body with a first end which is sealed; an opposing second end which is open; a bore and a wall which bounds the bore; and wherein the wall includes an inner metallic liner which faces the bore and an outer shell which is made from a composite material and which surrounds and reinforces the liner. 
     
     
         2 . The prop of  claim 1  wherein the liner is made from aluminium or an aluminium alloy, and the composite material comprises a reinforced plastics material. 
     
     
         3 . The prop of  claim 1  wherein the first end is sealed by a force transferring component and wherein the prop includes a one-way filler valve which is fixed to the body close to the first end and which is operable to allow a fluid under pressure to be introduced into the bore. 
     
     
         4 . The prop of  claim 3  which includes a tubular plunger which extends through the open second end into the bore, the plunger including a leading end with a piston and a seal, on the piston which is configured to engage in a sealing and sliding manner with an inner surface of the liner, the prop including a pressure relief valve which is configured to allow fluid under pressure in excess of a predetermined threshold pressure value to flow from an interior of the bore between the leading end of the plunger and the first end of the cylindrical body. 
     
     
         5 . The prop of  claim 4  wherein the pressure relief valve is mounted to the piston so that said fluid under pressure flows into an interior of the plunger. 
     
     
         6 . A support prop, comprising: a cylindrical aluminium liner which is externally reinforced with a shell made from a composite material; an aluminium plunger with a seal which engages with an inner surface of the liner; a filler valve through which a volume inside the liner, adjacent the seal, in use, is pressurized with a fluid; and a pressure relief valve which in use allows fluid under pressure to escape from the volume as the plunger is forced into the liner.