HYDRAULIC STEEL PROP

PCT No. PCT/DE89/00436 Sec. 371 Date Mar. 2, 1990 Sec. 102(e) Date Mar. 2, 1990 PCT Filed Jul. 1, 1989 PCT Pub. No. WO90/00217 PCT Pub. Date Jan. 11, 1990.Hydraulic steel mine prop having a bottom ram including an outer cylindrical tube (1) having a cylinder bottom (14) and an end collar (16), as well as a top ram guided coaxially slideably in the bottom ram by the end collar (16) and a guide ring (12). The top ram is a cylindrical tube (2) comprising a piston (9) sealed and guided relative to the inner wall of the outer cylindrical tube (1). A prop head (4), a setting and withdrawal valve (21), an inner extension stroke limiter, and a return spring (6) are also provided. Each of the outer and the inner cylindrical tubes is received at its facing ends by corresponding projections or facing end grooves of the end collar or piston at one end and at the prop head or cylinder bottom at the other end. Seals are provided at least at the piston, the prop head, and the cylinder bottom. An element is provided between the prop head and the piston for taking up tension forces between these two structural parts. A further tension element (7) arranged coaxially to the cylindrical tubes, is attached to the cylinder bottom. The element (7) extends as a holding rod through the piston and has a holding element (8) at its free end. A compression spring (6) is arranged coaxially to the tension element to act as a return spring.