Support prop

A support prop which includes:

• (a) an outer elongate tubular member with an inner surface, an interior bounded by the inner surface, a first end which has an open mouth, a second end, and a plate which is engaged with, and which seals, the second end,
• (b) an inner elongate tubular member with an outer surface, a leading end, a trailing end, and a closure which is engaged with, and which seals, the leading end,
• (c) the inner tubular member and the outer tubular member being aligned in an axial direction with said leading end being inserted into said open mouth so that the inner tubular member extends telescopically into the outer tubular member,
• (d) a seal which is engaged with the closure and which is in sliding contact with said inner surface whereby a volume in at least the outer tubular member is enclosed by a portion of said inner surface, the plate and the closure at said leading end,
• (e) an inlet valve, secured to the outer tubular member, through which liquid can be introduced into said volume thereby to pressurise the volume,
• (f) a pressure relief valve engaged with the closure, the pressure relief valve allowing liquid, in the volume, at a pressure in excess of a predetermined level, to flow from the volume through the pressure relief valve into said interior,
• (g) at least one wedge member located between opposing sections of said outer surface and said inner surface, and
• (h) wherein the inner tubular member is movable in said axial direction into the outer tubular member against a yielding force which is determined by
• (i) said predetermined pressure level, and
• (ii) deformation of the inner tubular member by the at least one wedge member which is movable, together with the inner tubular member, into the outer tubular member.