Hydraulic and earth engineering – Earth treatment or control – Shoring – bracing – or cave-in prevention
Patent
1992-01-06
1993-04-27
Taylor, Dennis L.
Hydraulic and earth engineering
Earth treatment or control
Shoring, bracing, or cave-in prevention
2483541, 405288, E21D 1544
Patent
active
052056767
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a hydraulic steel mine prop having a bottom ram substantially 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 the bottom ram.
BACKGROUND INFORMATION
In mine props of this type the top ram comprises substantially a cylindrical sealed relative to the inner wall of the outer cylindrical tube and which has a prop head at its other end. The top ram further includes an inner prop extension stop and a return spring formed as a screw spring which is secured with one end to the prop head and with the other end to the cylinder foot. The return spring passes through a bore in the piston, whereby a further tube which encloses the spring is arranged coaxially between the prop head and the piston. The piston includes a safety valve which relieves the pressure from the compression chamber when the piston assumes a predetermined end position.
A hydraulic steel mine prop as just described is known from German Utility Model Publication (DE-G) 8,808,519 corresponding to 5,051,039 (Heiliger). Props of this construction do not have an inner mechanical stop which limits the prop extension and takes up the prop extension force. Thus, one version of such props comprise a safety valve in the piston, which valve is operated by mechanical means in the desired end position for releasing the pressure from the compression chamber so that a further prop extension becomes impossible. The mechanical structure conventionally used for this purpose is, on the one hand relatively expensive, and on the other hand, the known structure permits only a passive switching of the safety valve. This means that the safety valve, due to its internal mechanical features, is operated at a switching point and not at all from the outside in a positive manner.
OBJECT OF THE INVENTION
It is the purpose of the invention to solve the problem of simplifying the operating mechanism for the safety valve and to construct this mechanism so that a positive operation of the safety valve is achieved.
SUMMARY OF THE INVENTION
Starting with a hydraulic steel mine prop of the type described above, the above problem has been solved according to the invention in that the spring is divided into two separate spring members which are interconnected by an intermediate member at the separation point, whereby the intermediate member comprises a flange extending outside of the outer spring diameter, said flange cooperating with an operating element guided at the piston in the desired end position of the piston for moving the operating element which in turn activates the safety valve.
Thus, rather very simple features are used, namely only the divided spring with the intermediate member. The spring functions simultaneously as a return spring and as a carrier for the intermediate member. The intermediate member itself moves slower than the piston due to its clamping in the spring when the prop is being extended so that the piston with the safety valve sometimes reaches the intermediate member. This position can be exactly predetermined by the arrangement of the intermediate member. When the intermediate member is reached, the operating element also reaches the intermediate member and is thus operated by the intermediate member due to the movement of the piston past the intermediate member. The intermediate member on its part operates now the safety valve in a positive manner. In this connection the operating element may quite easily be a crosswise extending slide member which engages the flange of the intermediate member while the piston passes the intermediate member, whereby the operating element is displaced crosswise and the crosswise displacement operates the safety valve. The intermediate member cannot escape radially even though it is mounted in the spring, because the intermediate member is guided in the tube that encloses the spring, whereby the intermediate member if it tries to radially yield, bears against t
REFERENCES:
patent: 1579913 (1926-04-01), Bronson
patent: 2621631 (1952-12-01), Dowty
patent: 4255071 (1981-03-01), Koppers et al.
patent: 5026218 (1991-06-01), Zimmerman
patent: 5051039 (1991-09-01), Heiliger
Fasse W. G.
Taylor Dennis L.
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