US2888230A - Roof supports - Google Patents

Description

May 26, 1959 A. W. DUNCAN ROOF SUPPORTS Filed June l5, 1953 flan! l l i 4 42 50 53 55 3l INVENTOR. ANGUS W. DUNCAN United States Patent O ROOF SUPPORTS Angus Wellesley Duncan, Worcester, England, assignor to The Mining Engineering Company Limited, Worcester, England Application June 15, 1953, serial No. 361,752 claims priority, application Great Britain June 16, 1952 1 Claim. (c1. 24a- 354) This invention concerns improvements in hydraulic roof supports of the kind employed in mines.

In props and other roof supports of the hydraulic type used in mining practice, it is common to tit a relief valve to limit ythe load which the prop can carry and to permit the support to yield as the roof pressure exceeds the load which the prop is designed to carry.

When such relief valves operate there is a substantial drop in the resistance olered by the prop which is undesirable for good roof control and it has been proposed to use valves of low hysteresis characteristics to reduce the drop in hydraulic pressure and thus to achieve, as far as possible, a prop olering constant resistance to roof pressure. I

One object of the present invention is to provide a mine roof support of the hydraulic type having improved resistance characteristics.

Furthermore, with roof supports which are self-setting and preloading (such for example as those described in my co-pending application No. 355,831) it may be, in certain circumstances, that the pressure exerted on the roof support by the convergence of the roof and oor does not reach the load at which the support is arranged to yield. Such a condition might obtain, for example, when the oor of the seam is so soft that the support penetrates the iloor at a load less than the yield load of the prop.

In such circumstances, the hydraulic accumulator, if arranged to work up to.or nearly up to the full Working pressure of the support, may not store a suicient volume of the working fluid to actuate the self-setting motor and to preload the support in its next settingv position. Another object of the invention is to provide a roof support in which it is possible to store sucient pressure lluid in the accumulator to operate a self-setting motor and to preload the support to a proportion of the rated loading even when the effective roof load acting on the support is less than the yield load.

From one aspect the invention provides an hydraulic roof support comprising a hollow ram constituting a uid reservoir operating in a cylinder, a relief valve connecting the cylinder to the reservoir and a hydraulic accumulator connectible for charging from the main cylinder underroof load.

The accumulator may have a working range yat least up to the pressure at which the relief valve operates whereby hysteresis losses in the valve are counteracted and resistance of the prop under bump roof conditions is maintained.

In other forms, the accumulator is of limited capacity and has a working range substantially lower than the pressure at which the relief valve operates so that the prop yields initially at the accumulator pressure up to the capacity of the accumulator and thereafter at ythe relief valve pressure.

From another aspect, the invention provides an hydraulic roof support comprising a hollow ram constituting a uid reservoir operating in a cylinder to which cylinder fluid is transferred fromv the reservoir by a pump to set the support and having a relief valve set to open at a predetermined pressure arranged between the reservoir and the cylinder and a hydraulic accumulator having a maximum working pressure at least equal to the maxi; mum pressure in the system and a minimum pressure slightly below the ypressure at which the relief valve operates, connected to the cylinder so as to be chargeable thereby, so that on a sudden increase in load on the support a proportion of the resultantpressure increase in the cylinder is absorbed in the accumulator whereby the pressure change to which the relief valve is subjected is reduced. f`

A pressure 'sensitive valve may be arranged between the accumulator and the main cylinder to close and isolate the accumulator when the pressure inthe system rises above the maximum pressure value of the accumulator pressure range.

The accumulator'may be of the spring type, air piston type or air bag type.

Other parts of the invention are embodied in the preferred form which will now be described in some detail with reference to the accompanying diagrammatic drawings in which Fig. l is a section through a self-setting preloading prop embodying an air bag type of accumulator;

Fig. 2 is a vertical section through the manually operable valve illustrating the accumulator charging position;

Fig. 3 is a vertical section similar to Fig. 2 illustrating the valve in position to expand the cylinder work chamber with the stored energy in the accumulator, and

Fig. 4 is a vertical section similar to Fig. 2 illustrating the valve in position to isolate the accumulator.

The prop as shown in Fig. l is of the self-setting preloaded type ,inA which the energy stored in the accumulator by roof subsidence is used to set the prop and also to exert a preload on the roof. It comprises a cylinder 20 in which a hollow ram 21 works with the ram and cylinder forming an expansible Work chamber 60 and the ram defining an oil reservoir 61 separated from the Work chamber by wall 62. A relief valve 22 yconnects the cylinder to the interior of the reservoir 61 by a passage 63 formed in the wall 62.

A hydraulic accumulator 23 of the air bag type is iitted to the support. The accumulator 23 comprises a llexible bag 30 containing air under pressure. The bag is housed in a chamber 31 and its maximum extension is determined by a guard plate 32 having holes 33 therethrough so that oil can pass through to exert pressure on the bag. A pressure sensitive valve 34 is interposed in the passage 42 connecting the accumulator to the manually operated valve and hence to the main cylinder Work chamber 60. This accumulator can be selectively connected to the work chamber 60 through ports in a manually operable valve 24 of the type shown in Figs. 2, 3 and 4, so that: the accumulator may be charged when the prop is com-J Fig. 2 shows the valve 24 pressed under roof pressure. in the accumulator charging position in which the cylinder work chamber 60k is connected to the accumulator so that the latter may be charged under roof pressure. After this occurs, valve 34 moves to the right as showin and isolates the accumulator. Port 41 in housing 40 of valve 24 communicates with work chamber 60, and port 42 communicates with the accumulator 31. In Fig. 2, port 41 is aligned with passage 43 in valve 24, which is aligned with port 44 leading to pressure sensitive valve 34 and thence to port 42. The space within cylinder 25 below piston 26 is in communication with the space above piston 26 by port 45, passage 47 in valve 24, port48 and passage 49 in wall of cylinder 25.

The accumulator is connectible through the Ymanually Patented May 26, 1959 operated valve 24 to exert pressure upon the upper surface of a piston 26 of an auxiliary cylinder 25 to raise the ram. The piston 26 is connected by a hollow rod 27 yto a larger piston 28 working in the reservoir. Pressure on the piston 26 thus puts pressure upon the fluid in the reservoir to transfer it to the main cylinder for the setting of the prop through the hollow rod 27 which communicates with the reservoir through a port 29 in a manner to be explained below. Fig. 3 shows the valve in position to raise the ram 21. In this position, passage 55 from accumulator 31 is aligned with passage 56 through valve Z4 and this passage 56 is aligned with port 48 leading to passage 49, in the wall of the cylinder. The space above piston 26 is thus put into communication with the oil under pressure in the accumulator and piston 26 moves downwardly bringing with it piston 28 and exerting pressure on the fluid in reservoir 61. Fluid then passes through port 29 down pipe 27 into cylinder 25 below the piston 26 and thence through port 45, passage 47 in valve 24 and port 57 into work chamber 60. The fluid pressure thus admitted to the work chamber then exerts force against the lower surface of wall 62 and on an additional surface 65, which moves the ram upwardly to extend the prop against the roof. When the prop is to be extended, it is obvious that the prop is initially collapsed and there is no pressure in work chamber 60.

The manually operable valve 24 can be set to isolate the accumulator from the cylinder as shown in Fig. 4. In this position, the accumulator 31 is isolated and main work chamber 60 is connected to the auxiliary cylinder 25 below piston 26 and thus to the reservoir 61 through port 57, passage 47, po-rt 45, rod 27 and port 29.

In operation, after the prop is initially set in position, valve 24 is set as shown in Fig. 2. The pressure sensitive valve 34 is biased into the position shown in Fig. l by spring 50. One end of valve 34 communicates with cylinder 25 through port 51, groove 52 around valve 24 and port 53, and the other end communicates with work chamber 60 through port 54 forming an extension of port 44. If, with valve 24 in the position shown in Fig. l, roof pressure forces ram 21 downwardly, the pressure below ram 21 increases, and so does the pressure in the accumulator 31. Valve 34 moves to the right, as shown in Fig. 2, closing the accumulator oi from the work chamber 60. Thereafter, pressure within the work chamber 60 can rise due to further depression of the ram 21 until relief valve 22 operates to allow oil to pass from beneath work chamber 60 to the oil reservoir within ram 21. Then when the support is to be moved, valve 24 is set into the position of Fig. 4 to lower the ram. When the ram is to be raised, valve 24 is set in the position shown in Fig. 3. With the valve 24 in this position pressure from the accumulator follows a path through passage 55, passage 56, port 48, passage 49 to act on the upper surface of piston 26 and urge it downwardly. This creates a pressure `in reservoir 61 because piston 2S is also urged downwardly by rod 27. Fluid in the reservoir 61 is forced to ow through port 29 and rod 27, through cylinder 25, port 45,V passage 47, and port 57 to create a pressure in work chamber 60. Since work chamber 60 and reservoir 61 are now in free communication, their pressures are equal. But, the pressure in work chamber 60 also acts on annular pressure surface and the ram is moved upwardly.

It is thus possible to store sufficient pressure fluid in the accumulator to operate a self-setting motor and yto preload the support to a propoltion of the rated loading even when the effective roof load acting on the support is less than the yield load.

It will be understood that, Where the hydraulic accumulator is of the air bag or similar type, it is a relatively simple matter to adjust its working range and, with an adjustable pressure sensitive valve, the roolf support can be adjusted to operate in practically all conditions likely to be encountered in mining practice.

Such adjustment of both accumulator and pressure sensitive valve may he accomplished after dismantling the support, or external means such asv the screw threaded plug 36 may be provided to make the adjustment without having `to dismantle.

It will be understood that the invention is not restricted to the details of the preferred forms which may be modified without departing from the broad ideas underlying them and dened in the accompanying claim.

I claim:

A hydraulic roof support comprising a housing having` a main cylinder, a ram operating in said cylinder and forming therewith an expansible work chamber, said ram being hollow and forming a separate fluid reservoir, a hydraulically loaded accumulator in said housing, said housing having a fluid communication passage between said cylinder work chamber andl said accumulator and through which the accumulator may be charged from the work chamber under roof load, said ram having a fluid communication passage between said cylinder work chamber and said reservoir, a nonreturn relief valve controlling said ram passage and operable to pass fluid from the cylinder work chamber to the reservoir, and a pressure sensitive valve controlling said passage between the accumulator and the main cylinder work chamber, said relief valve having an operating value at lease as great as the operating value of said pressure sensitive valve for controlling the working pressure-range of the accumulator relative to the pressure in the cylinder work chamber.

References Citedl in the le of this patent UNITED STATES PATENTS 1,510,462 Dell Oct. 7, 1924 1,812,577 Albertine Iunev30, 193.1 1,976,129 Johnson Oct. 9, 1934 2,555,427 Trautman June 5, 1951 2,584,820 Steinhol Feb. 5, 1952 2,597,050 Audemar May 20, 1952 2,621,631 Dowty Dec. 16, 1952 2,752,757 Joy July 3, 1956 FOREIGN PATENTS 493,811 Belgium Feb. 281950 1,016,105 France Aug. 20, 1952 608,054 Great Britain Sept; 9 1948`

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