Hydraulic double telescopic prop

Details Hydraulic double telescopic prop Hydraulic double telescopic prop

1999-04-12

2001-04-03

Lopez, F. Daniel (Department: 3745)

Motors: expansible chamber type

Extension of unit having separately controlled working...

Control of motive fluid for one working member in response...

C091S1700MP, C092S052000

Reexamination Certificate

active

06209440

ABSTRACT:

DESCRIPTION
A hydraulic double telescopic prop comprising an outer cylindrical casing tube, an inner tube which is displaceable therein and a piston rod which can be extended therefrom, having an outer annulus between the cylindrical casing tube and the inner tube and having an inner annulus between the inner tube and the piston rod, wherein the pressure medium can be fed under a piston of the inner tube and via a bottom valve under the piston rod in order to extend the two pressure stages, and can be fed into the outer and inner annuli for retraction.
Two-stage double telescopic props of the aforementioned type are used underground in mining in combination with hydraulic self-advancing supports. In order to support the exposed overlying stratum in a longwall face with a high shaft lining supporting force during the mining of coal, props of large volume are required, with a correspondingly high requirement for pressure medium. The construction of the props for static loading purposes is fashioned in accordance with the requirements imposed, and the prop tubes and piston rod are designed with suitable cross-sections and wall thicknesses. In turn, the dimensions selected have an effect on the sizing of the nominal diameters of the control valves and of the supply lines containing hydraulic fluid. These relationships ultimately determine the properties of a prop, which apart from the supporting force of the prop also include its drawing-in properties, which are important for shifting the wall lining during the reverse operation. For drawing-in, i.e. for retracting the placed prop, the pressure space in the outer cylindrical casing tube is connected to the return line to the tank, so that hydraulic fluid can drain off and the prop can sink. Hydraulic fluid is at the same time introduced into the outer annulus between the cylindrical casing tube and the inner tube. This hydraulic fluid acts on the ring area on the piston of the inner tube and pushes it in. The force which is generated on the small pressurised ring area for drawing-in the prop is slight, however. In contrast, a resistance to flow occurs in the control valve when the hydraulic fluid is expelled from the prop space of large volume, and moreover this resistance to flow is increased by a banking-up pressure in the return line if hydraulic fluid simultaneously flows into the return line from other consumers of hydraulic fluid.
The consequence is a slow sinking-in of the prop and a delay in the progress shaft lining shifting operation. A structural enlargement of the ring area would inevitably increase the external dimensions of the prop or would impair the static loading properties of the prop if it were carried out at the expense of the internal dimensions of the prop. Both of these effects are undesirable.
The present invention stems from background art from internal operations. According to this, hydraulic double telescopic props are constructed in such a way that the outer annulus between the cylindrical casing tube and the inner tube, which annulus is acted upon by hydraulic fluid during the drawing-in operation, has a relatively narrow aperture width, so that a size ratio of at least 10:1, which is unfavourable as regards the sinking-in behaviour of the prop, is achieved between the piston area of the inner tube and the ring area. On the other hand, the smaller size ratio of the inner ring area to the piston rod area remains unutilised, because the piston rod is generally not retracted during a shaft lining shifting operation.
The underlying object of the present invention is to fashion the static loading construction of a telescopic prop of the type cited at the outset, whilst retaining its external dimensions, in such a way that the force available for drawing-in is increased whilst the supporting force remains constant.
The double telescopic prop exhibits an advantageous relation of its dimensions to the form of the inner prop construction, in order to increase the ring area over the piston of the inner tube whilst the predetermined external dimensions and supporting forces remain unchanged, and in order to intensify the force for drawing-in the prop.
Since neither the requisite wall thicknesses of the prop tubes nor the piston rod diameter are changed, the static loading construction of the prop remains unchanged. The greater force is utilised for speeding up the drawing-in process, because at the higher liquid pressure a larger amount of liquid can also flow out of the pressure space of the prop into the return line. This saving in time when drawing in the prop speeds up the shaft lining shifting operation. There is thus an avoidance of delays in shaft lining such as those which occur in modern high output operations when a mining machine with a high cutting speed rushes ahead of the shifting of the shaft lining, because the shifting operation requires more time than does the mining of coal, so that the shaft lining remains behind.


REFERENCES:
patent: 1963286 (1934-06-01), Ballert
patent: 3241801 (1966-03-01), Wilkenloh
patent: 3696712 (1972-10-01), Sung
patent: 4523512 (1985-06-01), Hessel et al.
patent: 1 149 678 (1963-06-01), None
patent: 1 207 307 (1965-12-01), None
patent: 33 25 746 (1985-04-01), None
patent: WO 92/01858 (1992-02-01), None

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