Patent Application
20140050538
This invention relates to a prop suitable for use, for example, in an underground excavation in order to provide support between a footwall and an opposed hanging wall.
The specification of South African patent No. 95/6530 describes a prop of the aforementioned kind which includes two interengaged, telescopically movable, tubular members. A mouth of one member is flared. The other member enters the flared mouth and a conical friction ring is positioned in the flared mouth engaged with opposing surfaces of the tubular members. This prop can be prestressed by using hydraulic pressure which forces the tubular members telescopically apart. Yielding of the prop takes place, as one member moves into the other member, with the friction ring providing a restraining force against this telescopic movement.
Through suitable design and with the correct choice of materials a prop of the aforementioned kind can be constructed to withstand a substantial force e.g. of the order of 65 tons, before yielding commences. However, certain mining applications call for the capability of a prop to be loaded to a higher level, e.g. of the order of 100 tons, before yielding takes place. This figure is not readily attainable, though, when the conical friction ring is used as a restraining and, ultimately, as a yielding, member.
An object of the present invention is to provide a prop which attempts to address the aforementioned requirement.
The invention provides a prop which includes a first tubular member with a closed first end and a flared mouth at an opposed, second end, a second tubular member which extends into the first tubular member, through the flared mouth, which has one end inside the first tubular member and an opposed end which is sealed, a one-way filler valve connected to one of the tubular members through which a pressurised fluid can be introduced, at least, into an interior of the first tubular member, a seal which acts between the tubular members and which permits outward telescopic movement of the second tubular member relative to the first tubular member as an interior of, at least, the first tubular member is pressurised, a component which is located in the flared mouth around the second tubular member and which is frictionally engaged with, at least, an outer surface of the second tubular member, and a pressure relief valve which allows fluid to escape at least from an interior of the first tubular member, when the pressure of the fluid reaches a predetermined value, as the second tubular member is telescopically moved into the first tubular member.
The pressurized fluid may also be introduced into an interior of the second tubular member.
The seal may act between an outer surface of a part of the second tubular member which is positioned inside the first tubular member, and an opposing surface of the first tubular member.
Depending on the nature of the seal, fluid under pressure may be permitted to escape from an interior of the first tubular member into an interior of the second tubular member. Alternatively, fluid may escape from the first tubular member into atmosphere, or from the first and the second tubular members into atmosphere.
The invention is further described by way of example with reference to the accompanying drawing which illustrates from one side and in cross-section a prop according to the invention in an installed configuration.
The accompanying drawing illustrates a prop 10 according to the invention installed in an underground excavation 12 and positioned between a footwall 14 and a hanging wall 16.
The prop includes a first elongate tubular member 20 with a lower end 22 which is sealed by means of a domed closure 24. An opposing second end 26 of the first tubular member has an open mouth 28 formed by a flared section 30 of the member.
A second tubular member 34 is telescopically engageable with the first tubular member. The second member has a slightly smaller diameter than the first member to allow this type of interengagement. An upper end of the second tubular member is sealed by means of a domed closure 36. A lower opposed end 38 of the second tubular member is, in one embodiment of the invention, closed and carries a seal 40 which is in intimate sealing contact with an inner surface 42 of the first tubular member.
A conically shaped friction ring 44 is positioned inside the flared mouth 28 surrounding an opposing surface of the second tubular member. The ring carries formations, not shown, at least on its inner surface 46 which help the ring to engage frictionally with an outer surface 50 of the second tubular member.
A one-way filler valve 54 is attached at a suitable location to the first tubular member. Pressurised fluid, e.g. water, derived from a suitable source, not shown, is passed through the filler valve 54 using a suitable connection and an interior 56 of the second tubular member, up to the seal 40, can thereby be filled with water and can be pressurised.
With the prop in the orientation shown in the attached drawing, as the volume 56 is pressurised the tubular members are telescopically extended, moving, respectively, towards the footwall 14 and the hanging wall 16. In this way the prop is placed under a predetermined compressive load. Subsequently the friction ring 44 is hammered using a suitable tool, not shown, deeper into the conical mouth to ensure that it is firmly wedged in position and is frictionally engaged with the outer surface 50 of the second tubular member.
Normally, water is then allowed to flow freely from the volume 56 and, when yielding of the prop takes place, the yielding action is controlled by movement of the second tubular member into the first tubular member with the friction ring 44 tending to restrain such movement.
In accordance with one form of the present invention the pressurised fluid (water) is retained inside the volume 56. A pressure relief valve 60 is attached to the first tubular member. This valve will only open and allow water to flow from the volume 56 to atmosphere when the pressure of the water is in excess of a predetermined minimum. In other words the pressurised water restrains the prop from yielding until the water pressure exceeds a pre-set maximum value. At this point yielding is controlled by the combined actions of the pressure relief valve 60 and of the friction ring 44.
In a second form of the invention the pressure relief valve 60 is dispensed with and is replaced by a pressure relief valve 62 fixed to the closed end 38 of the second tubular member. The yielding action is, however, similar to what has been described but, in this event, once yielding commences, pressurised water is displaced from the volume 56 through the valve 62 into an interior 66 of the second tubular member.
In a third, preferred, variation of the invention neither of the valves 60 and 62 is used. Instead a pressure relief valve 64 is attached to a wall of the second tubular member. Additionally, an interior 66 of the second tubular member is filled with pressurised water at the same time as the first tubular member is pressurised. In other words a full interior of the prop contains pressurised water and thereby is pressurised. For this to occur a flow passage which permits free water flow is provided at the end 38 of the second tubular member. The seal 40 would then, for example, fit between an outer surface of the second tubular member, which is inside the first tubular member, and an opposed inner surface of the first tubular member. When the pressure of the water reaches a value at which the valve 64 opens, water is expelled to atmosphere through the valve. Yielding is controlled by the release of water from the prop and by the mechanical and frictional action of the friction ring 44 acting on the outer surface 50 of the second tubular member.
The two tubular members, included in the prop, can be made physically strong enough to withstand substantial loads. The prop can also be engineered, in respect of its slenderness ratio, so that it does not buckle when subjected to a high load. A yielding characteristic which is produced at a high load is, however, controlled by the combined action of the release of the pressurised water from inside the prop via the pressure relief valve 64 and by the mechanical/friction action of the ring 44.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012/06199 | Aug 2012 | ZA | national |
