US3541926A - Control system for a stepping hydraulic roof propping system - Google Patents

Description

United States Patent [72] Inventor Konrad Grebe Ant dem Nutzenberg 1, Wuppertal- Elberfeld, Germany 719,334

FOREIGN PATENTS 890,735 3/1962 Great Britain................ Primary Examiner-Paul E. Maslousky Attorney-Burgess, Dinklage & Sprung [21 Appl. No. [22] Filed April 8, 1968 Nov. 24, 1970 [45] Patented [54] CONTROL SYSTEM FOR A STEPPING HYDRAULIC ROOF PROPPING SYSTEM 20 Claims, 10 Drawing Figs.

ABSTRACT: Hydraulic mine roof prop of the stepping type having a plurality of chocks, each having a pair of frames which act alternately as propping members and stepping members, in which system check valves are prov with each frame through whic vided as supplied by the hydraul' frame props, and in which a pres sure is maintained. The stepping an frames are controlled from a central point W1 hydraulic lines.

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Sheet 1 016 I NVENTOR BY KONRAD GRE BE AT TORNEYS.

Pafiented New 24, 1970 Sheet I N VE N TOR KONRAD GREBE ATTYS. 7

Patented Nov. 24, 1970 Sheet 4 of6 INVENTOR KONRAD GRE BE ATTORNEYS.

Patented Nov. 24, 1970 Sheet INVENTOR Kormg GREBE M9 AT TURNEYS.

Patented Nov. 24, 1970 Sheet INAZE'NTOR KOAMDG E E CONTROL SYSTEM FOR A STEPPING HYDRAULIC ROOF PROPPING SYSTEM This invention relates to hydraulic mine roof props. It more particularly refers to such props made up of at least a pair of frames of props having stepping ability.

The invention more specifically relates to a control system for a stepping hydraulic roof propping system, which system consists of a plurality of chocks, each having two parallel frames, inwhich system the setting and disengagement'of the props is controllable from a main control station equipped with a pump system. The operation of the stepping actuating means is controllable from the same station by the use of controllable valves associated with frames. It is the purpose of the invention to simplify the control of the hydraulic system in roof-propping chocks and to improve the safety of such control system. ,4

In order to control a migrating prop system, it has been proposed to connect the props of all frames to a single feed conduit laid all across the prop breast; (that is the side thereof directed toward the direction of stepping motion) to provide one common valve for each pair of props in a frame, through which they receive the hydraulic fluid under pressure from this conduit; to provide this valve with a hand control by which the connection of the valve to the pressure conduit can be broken and the props can be connected by the operated valve to a prop disengaging conduit; and to provide one control conduit for each of the frames A and each of frames B through which the proper valves can also be remotely controlled from the main control station so that, by adjusting the pressure of one or the other control conduit, all frames A can be set and all frames B can be disengaged, or vice versa. The known valve assemblies have also been equipped with a check valve and a relief valveso that, in the event of any loss of pressure in the feed conduit running across the prop breast, the prop system will not collapse and, conversely, the props will be able to yield in-the case ofexcess roof pressure.

The stepping cylinders of the chock, that is the pistoncylinder assemblies which control and enforce the forward I movement of the chocks, are controlled in like manner. Two control conduits are required for the props, in addition to a feed line and a relief line; and another feed line, relief line and at least one more control line areneeded for the stepping cylinders. In the known construction, the valves that have to be used are very complex. Further, there is no provision for.

imparting maintenance pressure upon the frame that is being advanced or brought up to bear against the roof. It'is felt that this is essential, under certain conditions, to good care of the roof being propped.

In order to avoid these deficiencies, it has also been proposed in the past to control the valves associated with the frame or with the individual props by pressure differences which are produced at the main control station by varying the pressure in the feed conduit itself. In this case,the props ofone frame must, of course, be connected to a different feed conduit than are the props of the parallel, alternate frame. The conduits can serve alternately as feed conduits and as return conduits. In thiscase prop setting and prop disengaging valves,

designed as controllable check valves, are needed, which have such high pressure in their control chambers during prop setting that the valve is held open against the pressure of a Y the props in this system requires in any case a considerable expenditure of time. There is no provision whatsoever for maintaining an elastic bearing pressure, of a precisely predetermined magnitude, against the roofwhile the frame is being advanced or drawn up.

It is therefore an object of this invention to provide a novel roof-prop system.

It is another ob ect of this invention to provide a novel control system for a hydraulic roof prop.

-It is a further object of this invention to provide a novel stepping roof prop having a novel hydraulic control system.

Other and additional objects of this invention will become apparent from a consideration of this entire specification, including the claims and the drawing hereof. A

In accordance with, and fulfilling these objects, one aspect of this invention resides in a stepping hydraulic roof-propping system comprising at least one chock of props in two parallel frames; at least one stepping cylinder operatively associated with at least one of said frames; a'first conduit, adapted to carry hydraulic fluid, operatively associated with the props of the first of said frames; a second conduit, adapted to carry hydraulic fluid, operatively associated with the props of the second of said frames; a third conduit, adapted to carry hydraulic fluid, operatively associated with said stepping cylinder; check valve means, operatively associated with said conduits and said props; and central control means adapted to regulate the overall operation of the system.

The invention avoids the two difficulties of the prior art in that it does not use the necessarily invariable pressure of a spring to attempt to control a controllable check valve but, instead, controls such check valve by means of the pressure prevailing in another of the main hydraulic fluid conduits running along the breast. In this way, the check valve control piston can be put under pressure, or the pressure relieved as desired, according to the pressure conditions in another conduit. The device of this invention also avoids the difficulties of the 'prior art in that it sustains a certain elastic maintenance pressure of optional magnitude (2.3., 10 atmospheres gauge pressure or 5 atmospheres gauge pressure) in the conduit More particularly, this invention can be stated to comprise a control system for the stepping hydraulic roof-propping valve spring whereby allowing the hydraulic fluid to flow into the props. As soon as the pressure in the prop begins to equal the pressure in the valve chamber, the valve is closed by the pressure of the valve spring, and in the event of diminishing pressure in the feed conduit, and hence in the valve chamber, it thus remains closed. 7

The purpose of this prior art device is to cause the pressure in the feed conduit, and hence in the valve chamber, to diminish to such an extent, for the purpose of reversing the valve, that a spring acting in the opposite direction will act through a piston, that is if desiredunder the pressure of the outside air, on a plunger opening the valve. If we disregard the difficulty of producing a reduced pressure in the feed conduit, it is indeed possible, as long as the valve is closed, to produce system having a plurality of chocks of two parallel frames (A and B) each, which control system is operated from a main control station equipped with suitable pump installation. The props of frame A and the props of frame B are each connected to a main conduit running across the'breast of this system,

which serves alternately as a feed conduit and a return'con duit. Further there are provided controllable check valves associated with each of the frames inserted in these main con- 7 duits. The control pistons of the controllable check valves inserted into the related main conduit are controllable in each case by the pressure prevailing in the main conduit feeding the props of the other frames or feeding the prop advancing (stepping) cylinders. An elastic pressure of selectable magnitude is maintained in each case in the main conduit that receives the return flow of the hydraulic fluid from each of the props. v I

Understanding of this invention will be facilitated by reference to the accompanying drawing, in which:

FIG. 1 is a schematic view of two ch'ocks having a single FIG'. 1, showing one frame stepping FIG. 3 is similar to FIG. 2, showing one frame fully extended forward;

FIG. 4 is similar to FIG. 1, showing the sequence of frames engaging in an overtaking step (viewed from right to left);

FIG. 5 is similar to FIG. 1, showing a system with a stepping cylinder associated with each frame of props and one pair of frames fully extended;

FIG. 6 is similar to FIG. 5, showing one pair of frames partially extended;

FIG. 7 is similar to FIGS. 5 and 6, showing both pairs of frames substantially alined FIG. 8 is similar to FIG. 6, showing the other pair of frames partially extended;

FIG. 9 is similar to FIG. 8, showing the other pair of frames fully extended (FIGS. 5 through 9 show an overtaking step); and

FIG. 10 shows an enlarged, detailed schematic view of the conduits leading to the chamber of a stepping cylinder includ ing a step-limiting unit.

'As used herein above and hereinafter, the following terms have the following meanings:

from the point at which it was last set, and especially the advancing step of the leading frame in systems in which the same frame always steps forward and the other frame always overtakes it.

The following provisions are made in order to accomplish this invention, to achieve its desirable ends and in order to forestall the possibility of misoperation of this system: in addition to the main conduits leading to the props of frame A and to the props of frames B, a further main conduit is used, which leads to the chambers of the stepping cylinders on the working-face (breast) side of the advancing cylinders associated with the frames A and, if desired, an additional main conduit is used which leads to the working-face side of additional stepping cylinder chambers associated with the frames B for the performance of an overreaching step and, also, if desired, an additional main conduit is used, which leads to the chambers on the gob (rear) side of the advancing cylinders, and the pressure prevailing in each of these main conduits (1-5) is controlled such that they can be manually connected selectively to one of the common mains (I-IV) associated with the main control station. One of the mains is suitably fed by the pump system with the full prop setting power, the second main (and the third, if desired) is fed with the elastic roof-maintenance force of, for example, 10 (or 5, as the case may be) atmospheres gauge pressure for the advancing step (or overtaking step, as the case may be), and the last main has substantially no pressure therein.

The first of these common mains l is directly fed by the 7 pump system. It is provided with a pressure accumulator ad- 240 atmospheres (atm) gauge and with a pressure-limiting valve adjusted to the same pressure. The second, II and, if desired, the third III common main are fed by the pump system through a throttle and are provided with a pressure accumulator adjusted to the elastic roof-maintenance pressure, which is to be used in the frame-advancing step, and which may amount to, for example, 10 atm gauge (5 atm gauge for an overtaking step), and with a pressure-limiting valve adjusted to the same pressure. The last common main IV is not connected to the pump system, but only to the reservoir receiving the returning fluid, into which the other common mains also return any fluid that is passed by the pressure-limiting valves associated with them, in the case of any excess pressure.

Owing to the fact that the central control station has these common mains, one of which is always under the normal propsetting pressure, while one or two other common mains are constantly under a certain lower pressure intended only to hold the loose rock shingles during the advancement of the frames. There is accomplished the desirable proposition that a number of the main conduits running across the system breast can be connected through valves associated with them to the same common main, thereby avoiding misoperation due to pressure differences, as well as the tedious building up and easing down of the pressure in the conduits. Pressure differences between two main conduits would, for example, affeet the operation of the stepping cylinders, for example, if the chambers of the stepping cylinders were connected to individual main conduits and had different piston cross sections. If the pressure in one of the conduit systems thus created increases due, for example, to movements of the roof, the excess hydraulic fluid is delivered to the fluid reservoir at the control station through a pressure-limiting valve associated with the common main. The use of pressure reservoirs prevents an excessively frequent turning on and 'off of the pump system and the excessively frequent operation of the pressure-limiting valves associated with the control station, and it also provides a buffer against the occurrence ofjolting in the conduits.

The simultaneous setting of all frames A and of all frames B prevents disturbance of the roof and saves time without demanding greater output from the pump system. The maintenance of an elastic prop pressure when the frames are ad vanced not only assures better care of the roof, but also reduces the amounts of hydraulic fluid that have to be pumped in and out when the-props are set and disengaged.

If the main conduit 1 (2), which leads to the props of frame A (B), is connected to the common main 1 that is under the full prop-setting pressure, the props of all frames A (B) are automatically set. Even when the pressure is removed from this conduit-whether intentionally (by operation of the controls) or unintentionally (by the bursting ofa hose)they remain set providing the controllable check valves inserted into the conduit are not unseated due to pressure on their control piston from another main conduit. When this other main conduit is put under pressure, all of the check valves associated with frames A, or all those associated with frames B, can be anseated simultaneously.

As long as the check valves are not unseated, the pressure in the set'props can be increased by the effect of changing roof loads. If this pressure increase exceeds a certain amount, the excess pressure can be taken off in a known manner through a shunted pressure-relief valve and delivered to the main conduit feeding the props, even if this main conduit is still under the full prop-setting pressure, since this conduit is in turn equipped with a pressure-limiting valve at the main control station, and the excess amounts of hydraulic fluid are carried away to the fluid reservoir through this pressure-limiting valve.

If this pressure-relief valve is set for twice the prop-setting pressure, the carrying capacity of the prop can be raised to twice the prop-setting pressure. In order for the unseating of the check valves associated with the frames to be possible at anytime by the actuation of its control piston from a main line that is under the propsetting pressure, the operating pistons of these valves have a cross section that is such that it can open the check valve even against the a pressure that corresponds approximately to twice the prop-setting pressure.

If the controllable check valves are unseated, the pressure in the props automatically falls to the pressure that prevails in the main conduit feeding the props. If this main conduit, therefore, is connected to a common main II (III) having a pressure of 10 (5)-atmospheres gauge, the props of the associated frames are under an elastic roof maintenance pressure of 10 (5) atmospheres gauge.

Now, in order to be able to control the advancement of the self-propelled propping system simultaneously with the setting and disengagement of the props and do so from the main con- 'trol station with a minimum of expanse and a maximum of safety, the stepping cylinders are provided with a differential piston whose full piston'surface area, which is alternately loaded with the full pressure and relieved therefrom, faces the main control station. The gob-side chamber of the stepping cylinder, however, is connected to a main line that is constantly under pressure, and from which the gob-side chamber is filled with hydraulic fluid under pressure when the breastside chamber is emptied, and vice versa. If the breast-side chamber is pressurized, it is connected to the gob-side chamber by a closed conduit system so that the fluid flowing from the gob-side chamber is fed by the action of the differential piston to the breast-side chamber.

, ders, if they are each connected to this chamber through a The control system described is applicable both to a.

stepping prop system in which only frames A are advanced during the winning, and frames B are pulled up to them after the winning cycle has ended, and to a prop system whose frames overrun oneanother and push forward the conveyor and, in some cases, the winning apparatus, during each overrunning step. In the former case a stepping cylinder disposed in the area of the floor skids and/or a stepping cylinder disposed in the area of the roof bars are fixedly joined to frame A, and each of these stepping cylinders is longitudinally displaceable against, for example, a guiding element associated with the B frame of the chock and joined in a longitudinally undisplaceable manner thereto, according to the movements of the piston rod that can be extended from it and is attached to the guiding element at its extremity by a cross spar. In the second case, a stepping cylinder disposed in the area of the floor skids and/or in the area of the roof bars and joined to frames A in a longitudinally fixed manner is guided on an identical stepping cylinder associated in like manner with frames B and is displaceable longitudinally in relation thereto, the piston rods of these stepping cylinders, which are extendable in thedirection of the gob, are joined at their extremities by a cross spar.

Difficulties cannot occur in the operation of the stepping cylinders, because the ratio between the full piston face area associated with the breast-side chamber and the annular piston face area associated with its gob-side chamber is one that is permanently set, thereby positively determining the power differences that come into play even when the full hydraulic pressure is applied to the breast-side chamber, or

common alternating valve or through a controllable check valve whose control piston in this case, however, is fed with fluid under pressure from the main conduit in which the check valve is located. In this case these valves always open for the conduit that is under full pressure, but are held closed against the other conduit.

The gob-side chambers of the stepping cylinders, both in this system and in the alternative system proposed for it, in which they are connectedto a main conduit 3 that is always under full pressure, receive full pressure at all times on the annular piston surface. As soon as the breast-side chambers of the stepping cylinders are relieved of pressure, the pistons of the stepping cylinders are under a pressure acting in the direction of the breast; as soon as the breast-side chambers are connected to a main conduit that is under full pressure, the pressure which is exercised on the full piston cross section on the breast side in the direction of the gob predominates.

In further development of the invention, the breast-side chambers of the stepping cylinders which are not longitudinally displaceable in relation to frames A of the chock, and the control pistons of the check valves associated with frames A, are supplied by a main conduit 4. As long as main conduit 4 is at zero pressure, then, frames A cannot be disengaged, and the pistons of the stepping cylinders seek to draw up frames B. As soon as main conduit 4 is under full pressure, however, frames A can be disengaged, and the piston of the stepping cylinder seeks to push them forward in the direction of the breast.. V

In the case of roof-propping chocks which additionally have stepping cylinders that are associated with frames B and are substantially fixed in longitudinal relation thereto, the breastside chambers of the stepping cylinders associated with frames when the breast-side chamber is relieved of pressure while the If, in order to accomplish an overrunning step, the piston rods of one stepping cylinder associated with frame A and one associated with frame B of the roof propping chock are coupled together by a cross spar so that first the piston rod of the one cylinder can be pulled in and then the pistonrod of the other cylinder can be run out, then, in order to prevent the simultaneous extension of both piston rods, this ratio of piston face areas must be made such that the annular piston face has a cross section that is slightly more than half as large as the full piston face associated with the breast-side chamber. In this case a greater force is always available, too, for the advancement of frame A or B, as the case may be, than is available for the pulling up of frame B or A, respectively.

In order to keep the gob-side chamber of the stepping cylinder constantly under pressure, a main conduit 3 can be used which is constantly under pressure. But since either the main conduit 1 feeding the props of frame A of the main conduit 2 feeding the props of frame B must always be under full pressure, these two conduits can also alternate with one another in feeding the gob-side chamber of the stepping cylin- B and the control'pistons of the check valves associated with frames B are fed through a main conduit 5. In fact, in this case a dual valve is provided at the main control station, by which the main conduit 5 is in each case operated in common with the main conduit 4 in such a manner that main conduit 5 is always under full pressure when mainconduit 4 is switched to zero pressure, and vice versa.

Therefore, as long as the main conduit 5 is at zero pressure, the frames B cannot be disengaged, and the pistons of their stepping cylinders seek to pull frames A forward, which frames are then pushed further forward by thestepping cylinders with which they themselves are associated since their breast-side chambers are simultaneously fed by the main line 4. As soon as the main line 5 is under full pressure, however, the frames B can be disengaged, and the pistons in the stepping cylinders associated with the frames A, being relieved on the breast side, pull the frames B forward, whereupon the latter frames are pushed still further forward towards ,the breast by the extension of the pistons from the cylinders which are associated with the frames B.

Where there is no need for laying a main conduit 5 along the breast, the control pistons of the check valves associated with frames B can be fed by branch lines 1' of the main conduit 1- --either all simultaneously or in each chock separately. It is important, however, that frames B not be disengaged until the full roof supporting pressure has been achieved in frames A by the operation of main conduit 1. The same considerations, of course, apply when the control pistons of the check valves associated with frames B are fed by main line 5.

Therefore the branch line 1' should be operated successively and connected to the appropriate main conduit (each) through a valve which is not operated until all frames A are set.,Otherwisethe propping system could collapse because the 1 relieving of frames 8 could commence before frames A are set If all frames A or all frames B are to be advanced simultaneously or brought up simultaneously, all that is needed is to control the conduits at the main control station in order to bring about the desired movements of the roof-propping system. During the advancement of frames A, the main conduit l is connected with the common conduit that is under the elastic pressure of e.g., 1O atmospheres provided for the advancement, while main lines 2 and 4, as well as main line 3, if used, are shifted to full pressure (setting pressure) and main conduit 5, if used, is at zero pressure.

After the advancing movement of frames A is completed, main conduit 1 is switched to full pressure while the branches of the main line 1 which supply the props of frames A and the gob-side chambers of the stepping cylinders are connected in parallel. The branches 1' of main conduit 1 or which operate the control pistons of the check valves associated with frames B, and which are preferably operated successively, and the main conduits 2 and 4 are not switched over until the hydraulic fluid in main conduit 1 has stopped flowing.

During the forward movement of frames B, that is during their overtaking or their overrunning step, as the case may be, the main conduit 2 is connected to the common main that is under elastic maintenance pressure of, e.g., 5 atmospheres provided for the bringing up of frames B or under the elastic pressure of, e.g., l0 atmospheres provided for the forward step, as the case may be, main conduit 1 and main conduits 3 and S, if used, are under full pressure (setting pressure), and main line 4 is at zero pressure. After the frames B have reached their end position, main conduit 2 is shifted to full pressure, but main conduits l (5) and 4 are not shifted until the hydraulic fluid has stopped flowing in the main conduit 2.

Apparatus which indicate this pertain to the state of the art. So the switching about of conduits 4 and 5 does not take place until this requirement is met. This can also be assured by an automatic system.

In the case of roof-propping checks, in which frames A first advance and frames B are only brought up to them, no further explanation is needed after what has been said.

In the case of roof-propping chocks, however, in which an overrunning action takes place, the succeeding movements should again be explained. When the set frame A is one step ahead of the disengaged frame B, the piston rod of the stepping cylinder associated with frame A is extended, the piston rod of the stepping cylinder associated with frame B is retracted, and the gob-side chambers of both stepping cylinders are receiving pressure e.g. through main conduit 3). Main conduit 4, which had produced the advancement of frame A by delivering pressure to the breast-side chamber of the stepping cylinder associated with frame A, is now shifted to zero pressure, and main conduit 5, which is delivering pressure to the breast-side chamber of the stepping cylinder associated with frame B, is simultaneously shifted to full pressure. By retracting the piston rods of the stepping cylinders associated with frames A and then extending the piston rods of the stepping cylinders associated with frames B, frames B now perform their overreaching step using frames A as their points of support. If we take the pressure exercised on the breast side of a stepping cylinder associated with a frame B as 100, the pressure acting on the annular piston faces in the gob-side chambers of a pair of stepping cylinders guided one on the other (smaller piston face area, regardless of how high the hydraulic fluidpressure is) will be, for example, 55 each, and the pressure acting on the breast side on the piston of the stepping cylinder associated with frame A will be equal to 0. Since the pressure difference in the stepping cylinder associated with frame A, being 55, is greater than the pressure difference in the other cylinder, which amounts to only 45, and since the piston of the rear cylinder couldbe pushed out only if the piston of the front cylinder is simultaneously pushed out (although here there is a pressure amounting to 2 X 55 NO, as compared with the pressure of 1 X 100 1 X 0 100), first the piston rod of the stepping cylinder associated with frame A is completely retractedthe first step bringing frame B in line with frame A thus takes place in the same manner as the overtaking step of checks in which only frames A are equipped with stepping cylinders-then begins first the extension of .the piston rods in the stepping cylinders associated with frames B, causing frames B to perform their second step and also overrun frames A by the length of a full step. When frames B are then set, and frames A are disengaged, the reversal of main conduits d and 5 enables frame A to repeat the same overrunning step.

The control of these overrunning steps according to the invention offers the special advantage that at least one piston rod of the two stepping cylinders guided one on the other is completely pulled in, and only the piston rod of the stepping cylinder associated with the foremost frame is extended to a length corresponding to the distance which this frame has traveled in relation to the other frame from the basic position in which all frames are in line. ln this manner the danger is avoided that, due to some operator error, both piston rods might extend into the gob area, which would entail the possibility of damage to the unprotected piston rods.

This problem could also be solved (under the assumption that the ratio between the piston areas is the same) by having no pressure in the gob-side chamber of the stepping cylinder associated with frame A, while the same pressure prevails in the breast-side chamber of this cylinder, and at the same time blocking the emergence of the hydraulic fluid from the breastside chamber of the other stepping cylinder, which is fed with the prop-setting pressure, using a cock or a check valve for the purpose, or by feeding double the setting pressure to the said chamber.

By the invention, however, the control of the pistons of the stepping cylinder is wisely combined with the control of the setting and disengagement of the props.

In the control of a hydraulic roof-propping system, using chocks whose frames A are advanced in each case and whose frames B are then brought up to them, it is in the prior art to control the overtaking step in such a manner that these frames are not all brought up at the same time, but are brought up one after the other by means of a sequential control. If such a sequential control system is to be provided in the roofpropping system according to the invention, it is brought about by providing, in each branch section of main conduit 1 (5) feeding the control piston of a check valve associated with a frame B, a valve associated with the preceding chock, this valve opening automatically when frame B of the latter chock has completed its overtaking step. The rest of the requirements necessary for the drawing up of the next frame B have already been fulfilled by the central control described. As soon as the impulse is given for the disengagement of frame B, all the rest of the action takes place automatically, and as soon as frame B has been drawn up, the valve associated with this chock reverses itself so that the next chock can commence its overtaking step. The setting of the drawn-up frames B does not have to be performed until all frames 18 have been drawn up, because the roof is being supported by frames A. It is not necessary, nor would it be desirable in the interest of the preservation of the roof, for the setting of frames B to be controlled by the action whereby they are brought up. i

The cocks which control the sequential pulling forward 0 the frames can be mounted, for example, on a cross spar which connects the piston rod of the stepping cylinder associated with frame A to the guiding member associated with frame B. As soon as this piston rod is retracted, the overtaking step of frame B is performed. As soon as the cross spar contacts the stepping cylinder, the overtaking step is terminated and the contact between the cross spar and the stepping cylinder can produce the automatic reversal of the cock mounted on the cross spar.

lf frames B are placed'on the left side of frames A, looking in the direction of advancement of the roof-propping system, the sequential control can best progress from left to right along the breast. The collapse of the roof that occurs when a B frame is brought up can never damage the frame propelling apparatus of those chocks which have completed their overtaking step, because they do not extend beyond the frames between which they are located. The extended piston rods of the chock next following, however, are protected against falling rock because the collapse is limited by the left frame of the next chock, which has not yet been brought up, and which is providing full support to the roof right up to the moment of the beginning of the overtaking step.

If the overtaking frames B are on the right side of the advanced frames A, the sequential operation provided for the along the breast. When frames A are advanced, the piston rods of the stepping cylinders are again extended; the cross spars to which the cocks are fastened are thus left behind again by the stepping cylinders. By this movement, therefore, the cocks or valves can be automatically closed again, and when the next overtaking step begins they will accordingly be in the position necessary for the performance of the sequential operation.

The same sequential control is possible in a propping system having chocks whose frames overstep one another as they advance, each frame advancing in two phases, the first of which consists in drawing up a disengaged frame until it comes in line with the set frame (overtaking) and is brought about in practi cally the same manner as the overtaking step' of the roofpropping system just disclosed. The drawing up of the lefthand. frames of the chocks begins at the left end, and that of the right-hand frames at the right end of the breast, the branch conduits which produce the disengagement of the right-hand frames being operated successively from left -to right, and those which produce the disengagement of the right-hand frames being operated successively from right to left. The valves by whose opening the left frame of thenext chock is disengaged are located at'the right extremity of the cross spar joining the two piston rods on a pair of stepping cylinders. The disengagement of the right-hand frame, however, is performed through a valve which is mounted on the preceding chock on the right of the frame, at the left end of the cross spar. If stepping cylinders are associated both with the roof bars and with the floor skids, it is a question of expediency whether the disengagement of the next frame is controlled by a single valve that is associated with one of these pairs of stepping cylinders, or whether it is desired to assure, by the connection of two valves in tandem, that the overtaking movement of the preceding chock has been of equal length at the roof and at the floor.

in chocks using an overstepping action, the first phase ofthe step, in which frame B, for example, overtakes frame A, is followed, either immediately or after completion of the moving up of all other frames B, by the second phase in which frames B pass ahead of frames A. The valves which control the disengagement of frames B remain unaffected in this second phase. Neither are they affected by the setting of frames B or by the first phase of the overreaching step of frame A. It is not until the second phase of the overreaching step of frame A is being executed, which precedes the setting of frames A and the disengagement of frames B, that they are closed again by the automatic system provided for their operation, so that they can (and must) be opened again successively for the purpose of bringing up frames B.

It is, of course, possibly to divide the roof-propping system to be used in the breast into a number of successive groups, each of which is connected to a control station, for the purpose, for example, of accelerating the chock advancing procedure by having a large number of individual pumping units, and for the purpose of reducing the length of the main conduits. in this case the frames of the first group can be arranged in a mirror-image fashion in relation to the frames of the second group. If the caving system is used, these groups are controlled on the basis of principles that have already been explained in detail, in such a manner that the caving either begins at both ends of the breast and progresses toward the middle, or vice versa.

Just as additional controlling means can be associated with the individual chocks in the bringing forward of the frames, for the purpose of adapting the control system to the particular conditions prevailing, for example, where the caving method is used, it is possible, in further improvement of the invention, to provide additional controlling means on those frames which advance the conveyor and/or the winning apparatus, while still maintaining the principle of the central control system described, for the purpose of adapting the control of the propping system to the requirements which are imposed by the selection of the kind of winning machinery with which it is to cooperate If a cut having a depth amounting to the length of a full step is won out in each operation, all frames A or all frames B can be advanced simultaneously the length of a full step from the starting position. The control apparatus that has been described is entirely sufficient for this purpose. if a coal cutting machine is used, which gets out only half the length of a full chock frame step'in each cut, or if a coal plane or a cutting chain that has a still shallower depth of cut is used, it is desirable to limit the advancement of the frames after each cut of the winning apparatus to a partial step whose length corresponds to the depth of the cut of the machine. in this manner a separate cylinder for pushing forward the conveyor and the winning machine that may be carried on it becomes unnecessary, and on the other hand any jamming of the winning device between the conveyor and the breast is avoided as well. In this case a step-limiting unit is placed ahead of the breast-side chamber of each stepping cylinder, this unit having a metering cylinder whose right and left chambers are alternately fed by the main conduit that is under pressure, and

whose left and right chambers'are alternately emptied into the breast-side chamber of the stepping cylinder, while the emptying of the breast-side chamber of the stepping cylinder into the main conduit that is under zero pressure is performed through a conduit which bypasses the metering cylinder and which is automatically blocked by a simple check valve as long as there is any pressure in the main conduit in question.

The capacity of the chambers of the metering cylinder can be selected on the basis of the length that is to be covered by the advancing frame in each of its partial steps, and the breastside chamber of the stepping cylinder is fed an amount of hydraulic fluid in each step that is metered to it by one stroke or a certain number of strokes by the metering cylinder. The

flow of hydraulic fluid to the stepping cylinder is thus obtained exclusively through the metering cylinder, as its piston is shifted in the one direction or the other; the discharge of the hydraulic fluid from the stepping cylinder, however, is entirely unaffected by the step-limiting unit.

The movements of the piston of the metering cylinder are best controlled through a four-way valve, which either connects the right chamber of the metering cylinder to the main conduit and the left chamber of the metering cylinder to the breast-side chamber of the stepping cylinder, or connects the left chamber of the metering cylinder to the main conduit and the right chamber of the metering cylinderto the breast-side chamber of the stepping cylinder.

This four-way valve is in turn operated either from the control station through a control line, or it is operated mechanically by the'winning device as it passes by. The possibility of manual control can additionally be provided so that it will be possibly at any time to intervene as desired in the automatic advancing process because of special circumstances.

lnthe case of the operation of the four-way valves through a control line, these valves are preferably in the form of solenoid valves and are preferably operated in common and simultaneously through an electric control line.

At the same time it can be brought about that the partial steps of all of the frames that are being advanced will be of the same length if this control line is energized by the closing of contacts connected in series, which are operated by the pistons of the metering cylinders, and which close when the pistons have reached their right or left end position, as the case may be. This assures that all the frames will be advanced precisely the same distance each time. If stepping cylinders fed through step-limiting apparatus of this kind are provided both in the area of the roof bars and in the area of the floor skids, the assurance is simultaneously provided that the roof bars will advance precisely the same distance as the floor skids so that the frames will not be able to rack over.

If it is desired to cause one or the other frame to advance one partial step further than the other frames, the four-way valve of the step-limiting unit associated with this frame-can be operated manually. On the other hand, if a frame has been unable to complete'its partial step, or to perform it at all, on account of some interference, the associated metering cylinder will also have been unable to perform its full stroke. One of the contacts therefore, which have toclose in order for the command to advance to be given to all metering cylinders has not been operated so that the interference is immediately detectable at the control station. The elimination of the trouble can then be undertaken on the spot.

Whereas a uniform and simultaneous advancement of the frames can be achieved by the operation of the four-way valves from the control station, the mechanical operation of each individual four-way valve by the passage of the winning (mining) device can produce a sequential operation which is very similar in principle to the sequential control system described in connection with the overtaking step. The automatic matching of the advancing movements of the roofpropping system to the movements of the winning device is in that case of special value.

If a winning device is provided both at the roof and at the floor, the use of the step-limiting unit (whether it is controlled from the control station or by the winning device) is especially important in that a uniform, or approximately uniform advancement in both the roof area and in the floor area can be assured, independently of any differences in the hardness of the working face in the roof and floor areas, and even independently of any cavities that might develop in the roof area due to collapse of the coal.

The invention will now be described with specific reference to the accompanying drawings.

The control station shown in FIGS. 1 and Shas a pump system 11. According to FIG. 1, this pump system feeds a common main I, which is equipped with a pressure accumulator l2 and a pressure-limiting valve 13 adjusted to the propsetting pressure of, for example, 240 atm gauge, and it also feeds, through a throttle valve 14 (15), a common main II (III), which is provided with a pressure accumulator 12 U2") and a pressure-limiting valve I3 (13"), which are adjusted to the elastic pressure of, for example, (5) atmospheres gauge, which is provided for the advancing (drawing up) of the frames.

The control station of FIG. 5 is provided only with the common mains I and II. Furthermore, at each control station there are provided connections for the main conduits running along the breast, along with a hydraulic fluid reservoir 16, into which the hydraulic fluid can be discharged.

According to FIGS. 1 to 4, main conduits 1, 2, 3 and 4 are provided, and according to FIGS. 5 to 9- the main conduits are 1, 2, 4 and 5. The main conduit 1 is connected through a twoway valve 17 by which it can be connected as desired to a common main I or a common main II. The main conduit 2 is connected, according to FIG. 1, through a two-way valve 18, and, according to FIG. 5, through a two-way valve 18', by which it can be connected as desired to common mains I or III (II). The main conduit 3 is connected through a valve 19 to common main I, from which it receives constant pressure. The main conduit 4 is connected, according to FIG. 1, through a two-way valve 20 either to common main I or to a drain conduit emptying into fluid reservoir 16. According to FIG. 5 a dual valve 21 is used, which connects the main conduit 5 to the drain conduit when the main conduit'4 is connected to common main I, and connects the main conduit 4 to the drain conduit when the main conduit 5 is connected to the common main I.

The main conduit 1 feeds hydraulic fluid under pressure in all cases to the props of frames A through a controlled check valve 22, and the main conduit 2 inall cases feeds hydraulic fluid to the props of frames 8 through a controlled check valve 23. The return of the hydraulic fluid into the main conduits takes place when the check valves are unseated, or it takes place through the pressure- relief valves 24 or 25. The control pistons of the check valves 22 are operated in all cases from the main conduit 4. The control pistons of check valves 23 are operated from the branch conduits 1' of the main conduit 1, according to FIGS. 1 to 4, and according to FIGS. 5 to 9 they are operated from the main conduit 5.

The stepping cylinders associated with the frames A (B) have a gob-side chamber 26 (26) and a breast-side chamber 27 (27'). According to'FIGS. 1 to a, the gob-side chamber 26 of the stepping cylinders constantly receives fluid under pressure through main conduit 3. According to FIGS. 5 to 9, the gob-side chambers 26 and 26' of the stepping cylinders are fed through either of the main conduits 1 or 2, in which case hydraulically operated check valves 28 (28') are provided. These check valves are unseated as long as the main conduit with which they are associated is underpressure. If, however, this main conduit (e.g. 1) is without pressure, they are nevertheless held closed by the pressure which prevails in chambers 26 (26'), and in which is fed from the other main conduit (e.g. 2). The action is thus the same as if chambers 26 and 26' were constantly fed through their own main conduit 3. The method illustrated in FIGS. 1 to 4 for the feeding of fluid under pressure to chambers 26 (26) can be applied just as well in FIGS. 5 to 9, and vice versa.

A manually operated valve 29 controls the branch conduit 1' in FIGS. 1-4; If the branch conduit 1' isconnected by this valve to the main conduit 1, frame B of the first chock can be pulled up, thereby opening valve 30 associated with this chock; the pulling up of the next frame B opens valve 30, etc, Valves 30 and 30' are affixed to the cross spar 31, which connects the piston rods of the stepping cylinders to the guiding means 32. Valves ofthe same kind can be fastened to the cross spar 31' which connects together the end of the piston rods of a pair of stepping cylinders according to FIGS. 5 to 9.

The step-limiting means 33 indicated in FIGS. 1 to 4 can be used in the same manner on every stepping cylinder according to FIGS. 5 to 9, and can be placed ahead of their breast-side chambers 27 and 27'. Conversely, it can be omitted in a roofpropping system according to FIGS. 1 to 4. It is represented in detail on a larger scale in FIG. 10. It has a metering cylinder 34, a four-way valve 35, and a check valve 36.

The manner in which the main conduits 1-4 are connected to the common mains in the control station, in the case of a roof-propping system according to FIGS. 1-4, is represented by-FIG. 1 in that phase of its advancement in which the drawing up of the frames B hasjust been completed. The valve 18 is reversed and the frames B are urged against the roof by the pressure from the main conduit 2. As soon as the hydraulic fluid stops moving in conduit 2, the valves 17 and 20 are reversed, the main conduit 4 receives full pressure and the main conduit 1 is connected to the common main II; and the frames A accordingly step forward, as shown in FIGS. 2 and 3. At the same time, the valves 30, 30, etc., close, while the valve 29 is closed manually. The valves 30 (30') have an inlet a on their lower side which is charged by a branch line of conduit 1; an outlet or inlet 12 respectively, on the right side, which outlet or inlet is connected to conduit 1", and an outlet 0 opposite to the inlet a through which the hydraulic fluid can be ejected. They further have a rotatable stopcock which either connects the inlet a with the outlet 12 (FIG. 1 and valve 30 in FIG. 4), or'which connects the inlet b with the outlet 0 (FIG. 2 and 3 and valve 30' and 30" in FIG. 4). This stopcock is operated by a spring (not shown in the drawing) which always tends to rotate it to the last indicated (normal) position. The stopcock may contain a lever (not shown in the drawing), which lever acts together with the impact of the hydraulic cylinder in such a manner that the stopcock is rotated against the spring tension into a position such that the inlet a is connected with the outlet b, as $663 as the piston rod, on which the valve 30 (30') is positioned, is completely moved in the inlet pressure cylinder by the complete discharge of the pressure chamber 27 and charge of the pressure chamber 26. It is also possible, with other constructions, to provide that in the normal position of valve 30, 30' the inlet a is closed and conduit 1 connected with the outlet 0, that is discharged, and that in the position according to FIG. 1 the outlet is closed and the conduit 1 is connected with inlet a, that is charged with pressure by means of the main conduit 1.

After the complete extension of the piston rods to their final position, shown in FIG. 3, the valve 17 is reversed, and the frames A are thus set. When the hydraulic fluid in the main conduit 1 stops flowing, the valve 29 is reversed, so that the branch conduits 1' can again by pressurized, and the main conduit 2 is connected to a low pressure-fluid pumping by reversing the valve 18, and the main conduit 4 is switched to zero pressure by reversing the valve 20. Then one frame after the other is drawn forward as shown in FIG. 4. When all the frames B have been drawn forward, the condition represented in FIG. 1 is again reached.

The manner in which the main conduits 1, 2, 4 and 5 are connected to the common mains of the control station, in the case of a roof-propping system according to FIGS. 5 to 9 is shown in FIG. 5 in that phase of prop advancement in which the frames B have just completed their overreaching step. The main conduit 2, which during this step was connected to common main II, is now connected by reversing the valve 18 to common main l, and then the valve 17' and the dual valve 21 are reversed under the same conditions as set forth above. The reversal of the dual valve delivers full pressure to the main conduit 4, while the main conduit 5 is switched to zero pressure. The frames A perform their overreaching step according to FIGS. 5 to 9, and are then set against the roof by reversing the valve 17'. Then, after reversing the valve 18' and the double valve 21, the overreaching step of frames B again follows. The individual phases are the same as those in FIGS. 5 to 9, except that this time the advancing frames B pull themselves forward against the set frames A.

I claim:

l. A hydraulic roof-propping system comprising at least one pair of chocks of at least two parallel frames each consisting of a first and a second frame, with each frame containing at least one prop; a first main conduit operatively connected to the prop of the first of said frames; -a second main conduit operatively connected to the prop of the second of said frames; at least one controllable check valve means between each of said conduits and a frame associated therewith; means controlling said check valves operative from the pressure in a conduit other than the conduit associated with said check valve; ad-

vancing cylinder means operatively associated with each of said frames; means for actuating said advancing cylinders operative in relation to the pressure in said conduits; means to maintain a predetermined elastic pressure in said main conduit when such is used to relieve an associated frame through said check valve; hydraulic fluid pressurizing means; and control means therefor.

2. The system claimed in claim 1, wherein said frame advancing cylinders have a breast-side and a gob-side and including first additional main conduit means leading to said breast-side and second additional main conduit means leading to said gob-side.

3. The system claimed in claim I, wherein said props are operatively associated through conduit means with at least three mains, including a main having hydraulic fluid of full prop-setting power therein; at least one additional main having hydraulic fluid of elastic pressure power therein; and at least one further main which is substantially free of hydraulic fluid pressure. V

to have hydraulic pressure on both sides thereof.

6. The system claimed in claim 5, wherein said advancing cylinder means has a breast-side portion and a gob-side portion and wherein one of said piston faces is associated with said breast-side cylinder portion and the other of said piston faces is annular, smaller than said breast-side face and faces said gob-side cylinder portion.

7. The system claimed in claim 6, wherein said gob-side facing piston faceis substantially always under full hydraulic pressure, while the pressure on the breast-side facing piston face is variable.

8. The system claimed in claim 7, wherein said gob-side advancing cylinder portion is operatively associated with a c0nduit means carrying hydraulic fluid of full prop-setting pressure.

9. The system claimed in claim 8, wherein said gob-side advancing cylinder portion is operatively associated with said fullpressure conduit means associated with both of said frames through valve means operative to maintain the line open to the pressurized conduit.

10. The system claimed in claim 2, wherein the advancing cylinders have chambers which are longitudinally fixedly connected to one of said frame pairs, and wherein said check valve is controlled by the main conduit supplying the breastside chamber of said cylinders.

11. The system claimed in claim 1, wherein advancing cylinders are operatively associated with each of said frames, whereby forming a chock.

12. The system claimed in claim 11, wherein said advancing cylinders are each longitudinally fixedly connected to their associated frames, whereby forming a chock.

13. The system claimed in claim 5, including a piston operatively associated with each of said check valves and branch conduits between said first main conduit and said second con- 16. The system claimed in claim 15, wherein said step-limiting means has a metering cylinder having a right and a left chamber adapted to be fed alternately from a pressurized conduit and wherein said right and left-side chambers are adapted to alternately empty into a breast-side chamber of the associated advancing cylinder.

17;The system claimed in claim 16, including means for emptying the breast-side chamber of said advancing cylinder into a substantially pressureless main conduit through means which bypass said metering cylinder.

18. The system claimed in claim 17, including auxiliary check valve means operative to block said bypass means when said main conduit is pressurized.

19. The system claimed in claim 15, including a four-way valve means operative to control actuation of said advancing means.

20. The system claimed in claim 11, including a multiplicity I

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