US3306050A

US3306050A - Mine roof support

Info

Publication number: US3306050A
Application number: US357241A
Authority: US
Inventors: Andrews Thomas Desmond Hudson; Harding John Kammerer
Original assignee: Dowty Technical Developments Ltd
Current assignee: Dowty Technical Developments Ltd
Priority date: 1963-04-04
Filing date: 1964-04-03
Publication date: 1967-02-28
Anticipated expiration: 1984-02-28
Also published as: GB1016061A; DE1608492B1

Description

1967 T. o. H. ANDREWS ETAL 3,30

MINE ROOF SUPPORT File April 3, 1954 3 Sheets-Sheet l INVENTORa 1967 T. D. H. ANDREWS ETAL 3,306,050

MINE ROOF SUPPORT Filed April 5, 1964 5 Sheets-Sheet 2 Thomas 0. fifindrews &L K Haw/mg BY 9 d uM A'r-rorawevs Feb 1967 T. D. H. ANDREWS ETAL 3,306,050

MINE ROOF SUPPORT Filed April 5, 1964 3 Sheets-Sheet 5 INVENTORQ ATTORNEYfi United States Patent 3,306,050 MINE ROOF SUPPORT Thomas Desmond Hudson Andrews, Cheltenham, and John Kammerer Harding, Charlton Kings, Cheltenham, England, assignors to Dowty Technical Developments Limited, a British company Filed Apr. 3, 1964, Ser. No. 357,241 Claims priority, application Great Britain, Apr. 4, 1963, 13,356/63 14 Claims. (CI. 6145) This invention relates to roof support apparatus, suitable for use in mines, and including a series of advanceable roof supports.

The present invention provides roof support apparatus including a series of advanceable roof supports, each support including at least one fluid-pressure-operated prop device operable to set the support against the roof, a fiuidpressure-operated jack device operable to cause relative movement between the support and an anchorage, and a valve assembly operable to control the operation of the prop and the jack, and a pilot line connected to a source of fluid under pressure and to the valve assembly of each support in turn, the valve assembly of each roof support normally closing the pilot line to prevent the valve assemblies of subsequent supports in the series from being in communication with the pilot source, the pressurisation of the pilot line to one value causing an operation of one of the devices of the first support in the series and a predetermined change in pressure in the pilot line causing the valve assembly of the first support to open the pilot line and so bring the valve assembly of the next support in the series into communication with the pilot source, and so on throughout the series.

Pressurisation of the pilot line to the said one value may cause the jack of the relevant roof support to apply an advancing force to a conveyor extending along the series of roof supports.

Alternatively, pressurisation of the pilot line to the said one value may cause the relevant roof support to commence an advancing operation, for example by causing the release of the roof support from the roof by operation of the prop and the advance of the support by operation of the jack. It may be arranged that a predetermined change in pressure in the pilot line is necessary to cause the support to be reset against the roof by operation of the prop.

After a roof support has completed an advancing operation, a further change in pressure in the pilot line may be necessary to cause the valve assembly of that roof support to open the pilot line. The valve assembly of-each roof support may be prevented from opening the pilot line until the prop is exerting a satisfactory roof-supporting force after advance of the support.

A second pilot line may be connected to a source of fluid under pressure and to each valve assembly of at least some of the roof supports in turn, the pressurisation of the second pilot line to one value causing a jack associated with the relevant roof support to apply an advancing force to a conveyor extending along the series of roof supports, and a predetermined change in pressure in the second pilot line causing the valve assembly to open the second pilot line to the valve assembly of a subsequent roof support.

A datum pressure line maintained at a constant fluid pressure may be connected to each valve assembly to provide a datum pressure against which the pilot line pressure operates.

Two embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings of which,

FIG. 1 is a diagrammatic view of roof support apparatus with the hydraulic connections omitted,

3,306,050 Patented Feb. 28, 1967 FIG. 2 is a diagrammatic view showing the hydraulic connections between a power unit and the roof supports,

FIG. 3 is a diagrammatic view showing the hydraulic connections to the props and jacks of a root support,

FIG. 4 is a diagrammatic view showing the valve assembly of a roof support according to one embodiment and,

FIG. 5 is a diagrammatic view showing the valve assembly of a roof support according to the second embodiment.

Referring first to FIGS. 1 to 4 of the accompanying drawings, FIG. 1 shows roof support apparatus in a coal mine. A conveyor 1 extends along the working face 2 of the mine, and a cutting machine 3 situated between the conveyor 1 and the working face 2 travels along the working face 2. The cutting machine 3 is guided by the conveyor 1. A series of advanceable roof supports 4 are located on the opposite side of the conveyor 1 to the cutting machine 3 and the working face 2. Each roof support 4 includes a ground-engaging sole beam 5 carrying three double-acting hydraulic props 6, and the three props 6 carry a roof beam 5a (FIG. 3).

Each roof support 4 is connected to the conveyor 1 by a hydraulic single-acting jack 7 for advancing the roof support 4 towards the conveyor 1, and every fourth roof support 4 has a hydraulic double-acting jack 8 for advancing the conveyor 1 relative to the roof supports 4. Tire jack 8 is not connected to the conveyor 1 and engages the conveyor 1 only when applying an advancing force to it.

A hydraulic power unit 9 has a main pressure source 10 from which a line 11 supplying hydraulic fluid under pressure extends along the series of roof supports 4. Each roof support 4 has a valve assembly 12 connected to the supply line 11 by a branch supply line 13. A hydraulic fluid return line 14 also extends along the series of roof supports 4, and the valve assembly 12 of each roof support 4 is connected to the return line 14 by a branch return line 15.

The power unit 9 also includes two secondary

hydraulic pressure sources

16, 17. A pilot line 18 connected to the secondary pressure source 16 passes through the valve assembly 12 of each roof support 4 in turn. The secondary pressure source 16 is operable to pressurise the pilot line 18 to difierent predetermined values, as will be described later. A datum pressure line 19 extends from the secondary pressure source 17 along the series of roof supports 4, and the valve assembly 12 of each roof support 4 is connected to the datum pressure line 19 by a branch line 21. The secondary pressure source 17 operates to maintain a constant pressure in the datum line 19.

FIGS. 3 and 4 show a valve assembly 12 according to the first embodiment, the valve assembly including three main valve units A, B, C, a sequence valve D and a pilot valve E. Main valve unit A is connected by line 22 to a subsidiary valve assembly 23 including a control valve 24 for each prop 6. Each control valve 24 is connected to the main pressure chamber 25 of each prop 6 by a line 26. The subsidiary valve assembly 23 also includes a pressure relief valve 27 for each prop 6. The main valve unit A has a piston 28 and a piston valve 29. The main valve unit B is connected by a line 31 to three

lines

32, 33, 34. Line 32 is connected to the jack-contracting side of jacks 7, 8. Line 33 is connected to prop-contracting chambers 35 in props 6, and line 34 is connected to the prop control valves 24. Main valve unit B has one piston valve 36 urged in one direction by a spring 37. Main valve unit C is connected by a conduit 38 to the jack-extending side of jack 8, and has one piston valve 39 urged in one direction by a spring 41. Value units A, B and C are each connected to the branch supply line 13, the branch return line 15 and the branch datum line 21.

Sequence valve D is connected in, and normally closes,

the pilot line 18. Sequence valve D includes three

ball valves

42, 43, 44, and three pistons 45, 46, 47. A spring 48 urges the ball valve 42 in one direction. The ball valve 43 normally closes the pilot line 18. A line 49 connects ball valve 42 and ball valve 43 to one part of each of valve units B and C and to two parts of valve unit A. A line 51 connects ball valve 42 and an annulus of piston 47 to the branch return line 15. Also the branch datum line 21 is connected to ball valve 44.

Pilot valve F includes a ball valve 52 and two

pistons

53, 54, piston 53 being urged in one direction by a spring 55. Ball valve 52 is connected by a line 56 to valve unit C, and the branch return line is connected to line 56 by a nonreturn valve 57. A line 58 connects ball valve 52 to ball valve 44 and piston 47 of sequence valve D. A line 59 connects an annulus of piston 54 to one of the lines 26 leading from a prop control valve 24 to a prop pressure chamber 25.

The valve assembly 12 also includes four nonreturn valves 61 connected to the pilot line 18 to enable the advance of the series of roof supports 4 to be commenced from the left hand end or the right hand end of the series.

In this embodiment, each conveyor-advancing jack 8 is applying an advancing force to the conveyor 1 continually except when its roof support 4 is undergoing an advancing operation. FIGS. 3 and 4 show the parts of the valve assembly 12 in the positions in which the roof support is set against the roof and the conveyor-advancing jack 8 is applying an advancing force to the conveyor. Thus, valve unit C is connecting jack 8 and line 38 to the branch supply line 13, valve unit B is connecting line 31 to the branch return line 15, and valve unit A is connecting line 22 to the branch return line 15.

Assuming that FIGS. 3 and 4 show the valve assembly 12 of the first roof support in the series, starting from the left hand end of the series, the secondary pressure source 16 is operated to pressurize the pilot line 18 to a pressure equal to the datum pressure in the datum line 19 and datum branch line 21. This pressurizes the portion of the pilot line 18 extending from the left in FIG. 4, passing through a non-return valve 61 and passing ball valve 43 in sequence valve D to pressurise line 49. Piston valve 39 of valve unit C is moved to the left by the pressure of datum value in line 49 to connect the jack-extending side of jack 8 and conduit 38 to the branch return line 15 instead of the branch supply line 13, so that the jack 8 stops applying an advancing force to the conveyor 1. The pressure of datum value in line 49 acts on piston 28 and piston valve 29 of valve unit A. This results in piston 28 moving to the right to engage piston valve 29 and prevent its movement from the position shown in FIG. 4.

The pressure of datum value in line 49 moves piston valve 36 of valve unit B to the left to connect line 31 to the branch supply line 13 instead of the branch return line 15, thus pressurising

lines

32, 33, 34. Because of pressure in line 32, the jack 8 contracts and the jack 7 applies an advancing force to the roof support.

The pressure in line 33 applies a prop-contracting force on the props 6, and the pressure in line 34 acts on the pistons 62 of prop control valves 24 to open their ball valves 63, so that fluid escapes from the pressure chambers of the props 6 through the line 22 and valve unit A to the branch return line 15.

Thus the roof support is lowered from the roof by contraction of the props 6, and the jack 7 advances the roof support 4 towards the conveyor 1. Also, the resultant loss in pressure in line 59 allows datum pressure in datum branch line 21 to move piston 54 and ball valve 52 of pilot valve E to the left.

When the roof support 4 has been fully advanced, that g is to say when the jack 7 is fully contracted, the secondary pressure source 16 is operated to lower the pressure in the pilot line 18 and line 49 to half the value of the datum pressure in the datum line 19 and branch datum line 21. This lowering of the pressure in line 49 to half datum value allows piston valve 36 of valve unit B to be moved by the datum pressure in datum branch line 21 and spring 37 back to the position shown in FIG. 4, so that

lines

31, 32, 33, 34 are now connected to the branch return line 15 instead of to the supply line 13. Also, the piston 28 is now moved to the left by the datum pressure in datum branch line 21, allowing piston valve 29* to move to the left to connect line 22 to the branch supply line 13 instead of the branch return line 15. The pressure in line 22 opens the ball valves 63 of the prop control valves 24 and extends the props 6 to reset the support against the roof. When the props 5 are fully pressurised, the pressure in line 59 moves piston 54 of .pilot valve E to the right and ball valve 52 returns to the position shown in FIG. 4.

The secondary pressure source 16 is then operated to reduce the pressure in the pilot line 18 to zero, and the datum pressure in datum branch line 21 then causes piston valves 29 and 39 of valve units A and C respectively to return to the positions shown in FIG. 4. Thus the jack 8 resumes its application of an advancing force to the conveyor 1. Also, hydraulic fluid is displaced into line 56 by this movement of piston valve 39 of valve unit C and passes along line 58 to the sequence valve D in which it acts upon piston 47 to displace pistons 45, 46, 47 and

ball valves

42, 43, 44 to the left. Line 49 now communicates through ball valve 42 and line 51 with the branch return line. The left hand portion of pilot line 18 now communicates through ball valve 43 and nonreturn valves 61 with the right hand portion of pilot line 18 which leads to the next roof support. Also the datum branch line 21 now communicates through ball valve 44 with line 58 to hold the parts of sequence valve D in the left hand position.

Thus, by varying the pressure in pilot line 18 in the same manner as was described for the first roof support 4, the next roof support 4 in the series can be advanced, and so on throughout the series.

If it is also desired to be able to advance the series of roof supports 4 starting from the right hand end of the series, a line (not shown) must be connected from the secondary pressure source 16 directly to the valve assembly 12 of the extreme right-hand roof support 4 in the series. The arrangement of nonreturn valves 61 in the valve assembly 12 of each roof support 4 ensures that the pressure signal in the pilot line 18 coming through the sequence valve D of the previously advanced roof support 4 enters the correct part of the sequence valve D regardless of whether the signal comes from the left hand portion or the right hand portion of the valve assembly 12 shown in FIG. 4.

When all the roof supports 4 have advanced, the sequence valves D are brought back to the position shown in FIG. 4 by reducing the datum pressure in

lines

19 and 21 to zero.

The valve assembly 12 described with reference to FIG. 4 was suitable for use where the conveyor 1 is continually urged towards the working face 2 by the jacks 8. The valve assembly now to be described with reference to FIG. 5 is suitable for use where the conveyor 1 is not continually urged towards the working face 2, but is advanced a portion at a time in the manner known as snaking. FIGS. 1 and 3 are also applicable to the embodiment shown in FIG. 5, but FIG. 2 requires a further secondary pressure source and pilot line, and the valve assembly of FIG. 5 is different from the valve assembly 12 of FIG. 4. However, to avoid unnecessary complication, the same reference numerals will be used in FIG. 5 as have been used for the same parts in FIGS. 1 to 4.

Referring then to FIG. 5, the valve assembly includes three main valve units A, B, C, a support sequence valve D, a pilot valve E and a conveyor sequence valve F. The support sequence valve D is connected to the pilot line 18, and the conveyor sequence valve F is connected to a second pilot line 71 which extends from a third secondary pressure source (not shown) in the power unit 9 and is connected to the conveyor sequence valve F of each roof support 4 in turn. The secondary pressure source is operable to vary the pressure in the second pilot line 71 in a manner to be described.

Valve unit A includes a piston valve 72 and is connected to line 22, line 49, branch supply line 13, branch return line 15, datum branch line 21, and to valve unit B by a line 73. Piston valve 72 is urged in one direction by a spring 74. Valve unit B includes a piston valve 75 urged in one direction by a spring 76, and is connected to branch return line 15, line 73, branch supply line 13, line 49, line 31 and datum line 21. Valve unit C includes a piston valve 77 urged in one direction by a spring 78, and is connected to line 38, branch supply line 13, branch return line 15, line 49, and a line 79 connected to three parts of conveyor sequence valve F.

Support sequence valve D includes two

ball valves

81, 82, two pistons 83, 84, and a spring 85 which acts upon ball valve 81. Line 49 is connected to three parts of support sequence valve D, and is also connected to line 86 which includes nonreturn valve 87 and is connected to pilot valve E. Besides its connection to pilot line 18, support sequence valve D is also connected to pilot valve E by line 88. An accumulator 89 including a piston 91 urged in one direction by a spring 92 is connected by line 93 to line 86 and through a nonreturn valve 94 to branch datum line 21.

Conveyor sequence valve F includes two ball valves 95, 96, two pistons 97, 98 and a spring 99 urging ball valve 96 to the left. An accumulator 101 including piston 102 urged in one direction by a spring 103 is connected to conveyor sequence valve F by line 104, which is connected to branch datum line 21 by line 105 which includes a nonreturn valve 106. Line 79 is connected to line 105 through a nonreturn valve 107. Ball valve 96 is connected to branch return line by a line 108.

Pilot valve E includes a ball valve 109, two pistons 111, 112 and a spring 113 urging piston 111 in one direction. Ball valve 109 is connected to branch return line 15 by line 114. The other connections to pilot valve E have already been described.

FIG. 5 shows the various parts of the valve assembly in their positions when the roof support is set against the roof with neither of the jacks 7, 8 pressurised.

When pilot line 71 is pressurised to the datum value (starting from the left hand end of the series of roof supports), the pressure passes through the conveyor-sequence valve F and line 79 to move piston valve 77 of valve unit C to the right, and so bring the branch supply line 13 into communication with line 38. Therefore the pushing side of conveyor-advancing jack 8 is pressurized, and the jack 8 therefore applies an advancing force to the conveyor 1. Valve unit C is self-latching by reason of a line 115, and therefore will remain in the conveyor-pushing position when the pressure in pilot line 71 is removed.

The pressure in line 79 passes through nonreturn valve 107 and charges the accumulator 101. When the pressure in line 71 is removed, the accumulator 101 displaces fluid to cause piston 97, and hence also ball valves 95, 96 and piston 98, to move to the right against the force of spring 99. The movement of ball valve 95 opens the pilot line 71 to the next roof support having a conveyoradvancing jack 8.

Thus, if pressure is applied to and removed from pilot line 71 four times, the first four conveyor-advancing jacks 8 in the series of roof supports 4 will be pressurised in the conveyor advancing sense.

When the conveyor 1 has been fully advanced in front of the first roof support 4, this first roof support 4 can be caused to commence an advancing operation by pressurising pilot line 18 to the datum value. This pressure passes through support-sequence valve D to reach line 49. Thus pressure in line 49 charges accumulator 89 through line 93, returns valve unit C to the position shown in FIG. 5 so that the jack 8 stops pushing the convevor. and moves valve unit B to the left to pressurise

lines

31, 32, 33, 34 so that the props 6 lower and the jack 7 advances the roof support up to the conveyor 1. Also, since pressure in line 59 is now lost, datum pressure in line 21 moves piston 112 of pilot valve E to the right, and spring 113 moves piston 111 and ball valve 109 to the right. Valve unit A is not moved by the pressure in line 49, because of the connection by line 73 from valve unit B and to valve unit A.

When the roof support has fully advanced, pressure in pilot line 18 is reduced to half datum value to cause valve B to return to the position shown in FIG. 5. Pressure in line 73 connecting valve units A and B is therefore lost, and the pressure in line 49 then moves piston valve 72 of valve unit A to the left to cause the props 6 to be extended, thus resetting the roof support against the roof. When the setting pressure in the props 6 is satisfactory, the pressure in line 59 returns the parts of pilot valve E to the position shown in FIG. 5.

The pressure in pilot line 18 is then reduced to zero, and accumulator 89 displaces fluid through line 93, line 86, pilot valve E and line 88 to actuate sequence valve D to open the pilot line 18 to the next roof support.

When the conveyor 1 and all the roof supports 4 have been advanced, the conveyor-sequence valve F and the support-sequence valve D can be brought back to the position shown in FIG. 5 by reducing the pressure in the

datum lines

19 and 21 to zero.

If it is desired to advance a roof support other than the next in the series, this can be done either by manual operation of valve units A, B, C or by sending pressure pulses of half datum pressure along pilot line 18 so that the sequence valves D are successively caused to open the pilot line 18 without releasing their respective roof supports from the roof. When the desired roof support is reached it can be advanced by varying the pressure in the pilot line 18 in the described manner,

We claim as our invention:

1. Roof support apparatus including a series of advanceable roof supports, each roof support including at least one fluid-pressure-operated prop device operable to set the support against a roof, a fluid-pressure-operated jack device operable to cause relative movement between the support and an anchorage, a valve assembly operable to control the operation of the prop and the jack, and a fluid-carrying pilot line connected to the valve assembly of each support in turn and to a source of fluid under pressure operable to vary the fiuid pressure in the pilot line in a predetermined manner, the valve assembly of the first support in the series including means operable by the pressurisation of the pilot line to one value to cause the operation of one of the devices of the support and being operable by a predetermined change in pressure in the pilot line from said one value to cause the valve assembly of the first support to open the pilot line to the valve assembly of the next support in the series, and so on throughout the series.

2. Roof support apparatus according to claim 1 wherein the anchorage is a conveyor in front of the series of roof supports and the valve assembly of a roof support includes means operable by the pressurisation of the pilot line to one value to cause said jack to apply an advancing force to the conveyor.

3. Roof support apparatus according to claim 1 wherein the valve assembly of a roof support includes means operated by the pressurisation of the pilot line to said one value to cause the roof support to commence an advancing operation.

4. Roof support apparatus according to claim 3 wherein the valve assembly of a roof support includes means operated by the pressurisation of the pilot line to said one value to cause the release of the support from the roof by operation of the prop and the advance of the support by operation of the jack, and including means operated by a predetermined change in pressure in the pilot line from said one value to cause the support to be reset against the roof by operation of the prop.

5. Roof support apparatus according to claim 3, including means operable after a roof support has completed an advancing operation to respond to a further change in pressure in the pilot line to cause the valve assembly to open the pilot line.

6. Roof support apparatus according to claim 3 wherein a second fluid-carrying pilot line is connected to each valve assembly of at least some of the roof supports and to a source of fluid under pressure operable to vary the pressure in the second pilot line in a predetermined manner, the valve assembly of the first roof support to which the second pilot line is connected being operable by pressurisation of the second pilot line to one value to cause the jack of this roof support to apply an advancing force to the conveyor, and being operable by a predetermined change in pressure in the second pilot line to cause the valve assembly to open the second pilot line to the valve assembly of the next roof support to which the second pilot line is connected.

7. Roof support apparatus according to claim 1, including a main pressure operating line, and a datum pressure line maintained at a constant fluid pressure and connected to each valve assembly to provide a datum pressure against which the pilot line pressure operates.

8. A roof support system comprising in combination: a series of advanceable roof supports each including a fluid-pressure-operated roof support prop and a fluidpressure-operated advancing jack; operating fluid line means including a pilot line; and valve means coupled with said line means and with said roof supports and responsive to a first pressure in said pilot line to cause advance of a first one of said roof supports and responsive to a first change in pressure of said pilot line to a second pressure to condition a difierent roof support in said series for an advancing operation in response to a succeeding pressurisation of said pilot line to said first pressure and to disable said first support from undergoing a further advancing operation in response to such next succeeding pressurisation of said pilot line to said first pressure, whereby repeated cycling of the pressure in said pilot line between said first and second pressures causes sequential advance of said roof supports.

9. A system as defined in claim 8 wherein said roof supports each include conveyor advancing means, a second pilot line, and wherein said valve means includes means responsive to the sequential cycling of pressure in said second pilot line to cause sequential operation of said conveyor advancing means.

10. A mine roof support and conveyor advancing system comprising in combination: a plurality of advanceable roof support and conveyor advancing assemblies each having a fluid-pressure-operated roof prop, a conveyor advancing jack, anda support advancing jack; fluid pressure means including a pilot line having first, second, and third pressure conditions; and valve means coupling said pressure means with said assemblies and responsive to a first pressure in said pilot line to release said roof prop of a first assembly from roof supporting position and to operate said support advancing jack, said valve means being responsive to a second pressure in said pilot line following said first pressure to place said roof prop of said first assembly under pressure in roof supporting position, and responsive to a third pressure in said pilot line following said second pressure to pressurise said conveyor advancing jack of said first assembly and to condition a succeeding support assembly for similar operation in response to a succeeding cycling of the pressure in said pilot line from said first to said second, to said third pressure conditions.

11. A system as defined in claim 10 wherein said valve means includes a plurality of valve members each associated with one of said assemblies and holding the suc ceeding assembly non-responsive to pressure cycles in said pilot line until its associated assembly has been cycled through an advancing operation and the pressure in said pilot line assumes said third pressure.

12. A system as defined in claim 10 wherein said first pressure is greater than said second pressure and said second pressure is greater than said third pressure.

13. A system as defined in claim 12 wherein said pressure means includes a datum pressure line coupled with said valve means and maintaining a constant pressure equal to said first pressure.

14. A system as defined in claim 13 wherein said pressure means includes a main operating pressure line coupled with said props and jacks through said valve means.

References Cited by the Examiner UNITED STATES PATENTS 3,216,201 11/1965 Ki'bble et al. 6145.2 3,217,605 11/1965 Bolton et al. 61-45.2 X

CHARLES E. OCONNELL, Primary Examiner.

JACOB SHAPIRO, Examiner.

Claims

1. ROOF SUPPORT APPARATUS INCLUDING A SERIES OF ADVANCEABLE ROOF SUPPORTS, EACH ROOF SUPPORT INCLUDING AT LEAST ONE FLUID-PRESSURE-OPERATED PROP DEVICE OPERABLE TO SET THE SUPPORT AGAINST A ROOF, A FLUID-PRESSURE-OPERATED JACK DEVICE OPERABLE TO CAUSE RELATIVE MOVEMENT BETWEEN THE SUPPORT AND AN ANCHORAGE, A VALVE ASSEMBLY OPERABLE TO CONTROL THE OPERATION OF THE PROP AND THE JACK, AND A FLUID-CARRYING PILOT LINE CONNECTED TO THE VALVE ASSEMBLY OF EACH SUPPORT IN TURN AND TO A SOURCE OF FLUID UNDER PRESSURE OPERABLE TO VARY THE FLUID PRESSURE IN THE PILOT LINE IN A PREDETERMINED MANNER, THE VALVE ASSEMBLY OF THE FIRST SUPPORT IN THE SERIES INCLUDING MEANS OPERABLE BY THE PRESSURISATION OF THE PILOT LINE TO ONE VALUE TO CAUSE THE OPERATION OF ONE OF THE DEVICES OF THE SUPPORT AND BEING OPERABLE BY A PREDETERMINED CHANGE IN PRESSURE IN THE PILOT LINE FROM SAID ONE VALUE TO CAUSE THE VALVE ASSEMBLY OF THE FIRST SUPPORT TO OPEN THE PILOT LINE TO THE VALVE ASSEMBLY OF THE NEXT SUPPORT IN THE SERIES, AND SO ON THROUGHOUT THE SERIES.