Hydraulic steel mine prop

A hydraulic steel mine prop, comprising a bottom ram including an outer cylindrical tube with a cylinder foot at one end and a collar ring at the other end, and further including a top ram coaxially guided in said bottom ram, said top ram comprising a cylindrical tube having at its one end a piston that is guided in and sealed relative to the inner wall of the outer cylindrical tube and which has a prop head at its other end, said top ram further including an inner prop extension stop and a return spring formed as a screw spring which is secured with one end to said prop head and with its other end to said cylinder foot, said return spring passing through a bore in said piston, whereby a further tube which encloses said screw spring, is arranged coaxially between said prop head and said piston, said piston including a safety valve which relieves pressure from a compression chamber when said piston assumes a predetermined end position, wherein said screw spring is divided into two separate spring members (11, 12) which are interconnected by an intermediate member (13) at a separation location, said intermediate member (13) comprising a flange extending outside of an outer spring diameter, an operating element, said flange cooperating with said operating element guided by said piston (5) in a desired end position of said piston for moving said operating element which in turn activates said safety valve (9).