GB2214988A - Control system for hydraulic mine roof support - Google Patents

Abstract

A hydraulic mine roof support having hydraulic legs 10 and 11, is supplied with fluld from a low pressure, high volume, supply via lines 12, 13, 26 during the stage of compacting loose material, and with fluid from a high pressure, low volume, supply via line 24 only for the final setting of the support, after compaction of loose material has been substantially completed. Initially fluid at low pressure is supplied via lines 12, 13 and when there is a pressure build up in the lines 12, 13 valves 29, 31 will be opened against spring bias and allow further fluid at low pressure to pass via line 26, restrictor 34 and valves 29, 31 to the legs. This latter flow will continue even if a dead man's handle controlling lines 12, 13 is released. When the pressure in lines 12, 13 has reached a significantly higher value the valve 33 is opened against spring bias to permit high pressure fluid from line 24 to flow to the legs 10, 11. <IMAGE>

Description

VALVE MEANS The Invent ion relates to valve means, and particularly to valve means for use wlth hydraulic mine roof supports.

In the well known longwall method of mining, a row of hydraulic mine roof supports is placed In a side by side relationship along a mineral bearing face, connected to a mineral carrying conveyor which extends along the face. As mineral Is cut away by a machine travelling along the conveyor, supports are successively used to advance the conveyor into a newly cut area, by means of hydraulic Jacks extending between the supports and the conveyor, are then lowered successively from the roof to free them from the roof, are advanced to a new positlon adjacent to the conveyor, by use of the aforesaid ram, and are then reset to engage the mine roof by extending the hydraulic legs of the supports.

The raising of a support to reset the support Is generally under the control of a mine operative, operating a dead man's handle. Once it appears to the mine operative that the roof engaging canopy Is In contact wlth the roof, he releases the dead man's handle and moves on to the next support. It may be however that although the support appears visually to be firmly in contact wlth the mine roof, it has not In fact fully engaged the roof, and the full working pressure has not been built up within the hydraulic legs.

With a vlew to reducing this problem, a system has been developed known as the "Positive Set" system in which operation of the dead man's handle opens a positive set valve which by-passes the dead man's handie. If the dead man's handle Is released too soon, hydraulic fluid continues to flow through the positive set valve from a high pressure source until the desired working pressure has been achieved in the hydraulic legs.

This positive set system generally works well, using two sources of pressure fluid supply. When the dead man's handle is first operated, a low pressure source provides the high volume supply needed to raise the legs almost to the roof. As soon as some resistance Is encountered, the rise In pressure causes the positive set valve to open, and the second high pressure source provides the low volume supply needed to complete the setting of the support. After setting, the high pressure supply may be discontinued, with the positive set valves returning to their closed positlons, or alternatively they may be arranged to remain in a state which causes the fluid to be topped up if a leak occurs in the circuit of the hydraulic legs.

However, a problem can arise when a significant amount of mineral Is not removed from the face workings, but, as frequently happens, remains as loose materlal above and/or below a support as It is advanced towards the mineral bearing face, to a new locatlon alongside the mineral conveyor.

it Is frequently not possible to remove this relatively loose materlal, but Its presence can be detrimental to the effective working of the hydraulic roof supports. When a mine operative believes that a mine roof support is properly set, from visual observation, he may release the dead man's handle, although the mine roof support is in fact resting on loose material and/or has loose material on its uppermost surface between the roof engaging structure and the mine roof proper.

The resistance which Is provided by this loose materlal may cause the pressure In the hydraulic legs to rise to a level sufficient to open the positive set valves. Thus further fluid is drawn from the second, higher pressure supply, which Is only Intended for low volume supply. Before the roof supports can bear their full working load, the loose material below and/or above the support must be compacted, and, depending upon the amount and nature of the loose material, total compaction may involve some 70mm of extension of the legs. Thus a relatively high volume of fluid may be drawn from the high pressure supply and this additlonal demand on a high pressure pumping system may be so severe that the effective operation of subsequent supports is at risk.

For example, one support may not yet be fully set, and may still be compacting loose material, when there is a further high pressure fluid requirement for the next adjacent roof support in the sequence and the pumping system may not be adequate to provide the necessary volume of fluid.

For example, If a given mine roof support has two supporting legs, each in the form of a hydraulic Jack, and each on a separate hydraulic circuit, and in turn each circuit has a positive set valve fed from a single high pressure supply line along the line face at 4500 psi, and a low pressure line at 3000 psi, with the positive set valves set to open at 1000 psl, a typical high pressure pump for this purpose would be designed to provide 32 litres per minute, or seven gallons per minute.

In this example the positive set valves would start to feed the supporting Jacks wlth high pressure fluid when opened and this would complement the low pressure feed up to the available pressure from the low pressure line. This pressure might not reach 3000 psl, If the demand was excessive and there Is insufficient flow to supply the requirements of other roof supports.

After the avallable pressure has been achieved, the high pressure feed then takes over, and acts Independently thereafter until the supporting Jacks reach full setting.

Under normal mining conditions, the time taken from the actuation of valve means, to the Jacks reaching the pressure of the higher pressure supply, may only take a few seconds, and consequently the early demand on the high pressure line would be low. However, in particular conditions described above, where there may be considerable loose material below and/or above the roof support, it can be predlcted that the high pressure feed system will be required to supply a substantial proportion of the total demand by the tlme the pressure in the supporting Jacks has reach 1700 psi. As a result, It can be anticipated that the required setting pressure will never be achieved, because, by the time that the pressure in the Jacks has reached 1700 psi, the positive set valve on the next support in the sequence will have been triggered and consequently will already be drawing high pressure fluid from the same source. This rapid actuation of the valve will be repeated on the next roof support and similarly on all further roof supports in the installation.

Calculations of flow rates, and demands on the supply from the high pressure feed line, under the adverse conditions described above, are dependent upon too many varlable for precise calculation. A simple approach may however be based on the anticipated extenslons of the supporting Jacks for initial compaction of the loose material up to a polnt where a positive set valve would be triggered and the further required high pressure fluid supply to attaln full compaction and load bearing. These calculations indicate that a high pressure supply of some 33 litres per minutes would be required to comply with the rate of one roof support being advanced every 12 seconds.Existing high pressure supply systems provide of the order of 32 litres per minute and so it becomes apparent that even slight variations In demand from the high pressure system would result in the roof supports not belng set as required, unless other factors are present such as a delay occurrlng in the setting of one support to the next, or a second high pressure supply being made aval lable.

Neither of these solutions are deemed acceptable to meet output requirements, and it would be expensive to Increase the high pressure pumping capacity.

We have now developed valve means which enables the rate of advancing of the supports sequentially to be maintained, with correct setting of the roof supports, even under loose conditlons, and without the need to increase the high pressure fluid supply.

Accordingly, the Invention provides valve means for connection to a first fluid source and to a second, higher pressure, fluid source, the valve means being such that when it is subJected to fluid pressure above a first predetermined level, it supplies fluid from the first pressure source and when It is subJected to a fluid pressure above a second, higher, pre-determined level, the valve means supplies fluid from the second fluid source.

The use of this valve means with a hydraulic mine roof support makes it possible to use fluid from a low pressure, high volume, supply during the stage of compacting loose materlal, so that fluid from a high pressure, low volume, supply is only used for the final setting of the support, after compaction of loose material has been substantlally completed.

Preferably the valve means Is connected to a supply conduit which, in use, is provided with fluid, for example, from under the control of a dead man's handle, along a first fluid path, the valve means belng such that when the said first pressure -level Isexceeded, the valve allows fluid to flow from the first source along a second fluid path to said conduit, and when said second pressure level is exceeded, the valve means allows fluid to flow from the higher pressure source along a third fluid path to sald conduit.

The valve means may be such that when in use relatively low pressure fluid Is fed via a non-return valve to the said conduit, when the first pressure level Is exceeded a first control valve is opened allowing additional fluid from the same low pressure source to flow Into the said conduit via a second non-return valve, and when the combined flow exceeds the second pressure level a second control valve Is opened which allows higher pressure fluid to enter the conduit and close the non-return valves whereby a third pre-determined pressure In the conduit may be obtained.

The conduit may comprlse the feed line Into a hydraulic supporting Jack of a mine roof support, and the low and higher pressure fluid sources may comprlse the main low pressure and high pressure feed lines from a pumping statlon located at the end of a longwall mining face, supplying pressure fluid to each support of an installation.

Valve means may be such that the first control valve, once opened, remains open until the final pressure in the supporting Jack has been attained, and the second control valve, once opened, remains open for the same duration.

The second control valve may be of a pilot operated form, and may embody two non-return valves and a restriction means.

The second valve may be arranged so that low pressure fluid passes through one of sald non-return valves and higher pressure fluid passes through the other non-return valve.

The invention includes a hydraulic mine roof support fitted with valve means according to the invention.

The valve means may be arranged to feed fluid to all the supporting Jacks of the mine roof support simultaneously.

By way of example, a specific embodiment of the invention will now be described, with reference to the single accompanying figure, which is a diagrammatic view of an embodIment of valve means according to the inventlon, connected to two hydraulic Jacks of a hydraulic mine roof support.

The drawing shows a diagrammatic front leg 10 and and a diagrammatic rear leg 11 of a mine roof support.

Slnce the remainder of the mine roof support Is conventional, It is not shown In the drawing, but It will be appreciated that It comprises a floor engaging base and a roof engaging canopy Interconnected by the hydraulic legs. In practice there may be two front legs 10 and two rear legs 11, but the operation of the legs will be Identical.

In normal I operation, a main control valve (not shown) manually operated by means of a dead man's handle, supplies fluid from a first source, to the legs 10 and 11, vla two supply conduits 12 and 13. This first source Is a low pressure high volume supply.

The conduit 12 is connected to the leg 10 via a non-return valve 14. The conduit 13 Is connected to the leg 11 vla a non-return valve 15.

The legs 10 and 11 have exhaust lines 16 and 17 through which fluid exhausts as the legs are ralsed.

When the legs are to be lowered, fluid is supplied through the lines 16 and 17 to retract the legs 10 and 11, and this In turn causes fluid to be fed via pilot lines 18 and 19 to ralse the non-return valve members of the valves 14 and 15 off thelr seats, so that return fluid can exhaust through the lines 12 and 13.

The valve means according to the invention comprises a pair of positive set valves 20 and 21, and a dual feed valve 22.

The valve 22 is connected vla line 24 to a second source of fluid pressure which Is a high pressure low volume source. The valve 22 Is also connected vla a nonreturn valve 25 to the first pressure source, via a line 26. Isolator valves 27 and 28 are provided should it be necessary to disconnect the mine roof support from the pressure sources, for example for replacement or repalr of the mine roof support.

The positive set valve 20 comprises a spring loaded pilot operated valve 29 and non-return valve 30.

The positive set valve 21 comprises a spring loaded pilot operated valve 31 and a non-return valve 32.

The dual feed valve 22 comprlses, in additlon to the non-return valves 23 and 25, a sprlng loaded pilot operated valve 33 and a restrictor 34.

When the roof engaging canopy of the mine roof support first encounters any obstruction, and thus appears visually to be set to the roof, there is a pressure build up in the lines 12 and 13 which causes the valves 29 and 31 to be opened, against the action of their springs, via pilot lines 35 and 36. Opening of the valve 35 opens an alternative path for low pressure fluid to the leg 10 via the line 26, non-return valve 25, restrictor 34, and non-return valve 30. Slmilarly, there Is an alternative path for the supply of low pressure fluid to the leg 11, vla the line 26, non-return valve 25, restrictor 34, line 37, and non-return valve 32.

Even If the operative releases the dead man's handle at this point, the pressure in the alternative supply routes will close the non-return valve 14 and 15, will continue to supply fluid to the legs 10 and 11, and will maintain the valves 29 and 31 in the open condition.

The sprlng of the valve 33 Is arranged to be stronger than the sprlngs of the valves 29 and 31, so It is only when a significantly higher pressure Is reached In the supply line to the leg 10, indlcating that the compactlon of any loose material is complete, that the valve 33 Is opened, agalnst the action of its sprlng, vla a pilot line 38.

Opening of the valve 33 makes available the high pressure, low volume supply which is needed to finally set the legs 10 and 11 to their full working pressure.

The restrictor 34 prevents too much fluid from being drawn off, thus possibly starving adJacent supports which might be actuated.

Slnce the invention ensures that the high pressure, low volume supply Is only used for the i fInal setting of the supports, after any compaction of loose material and hence substantlal travel of the legs, has been completed, there Is no excessive demand on the high pressure source and it Is possible for existing high pressure systems to supply all the demand that Is necessary to achleve rapid, high pressure setting of all the supporting Jacks extending along a mine face.

The contents of all papers and documents filed concurrently with this specification are incorporated herein by reference.

All of the features disclosed In this specification (Including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined In any combinatlon, except combinatlons where at least some of such features and/or steps are mutually exclusive.

The invention Is not restricted to the details of the foregoing embodiment(s). The Invention extends to any novel one, or any novel combination, of the features disclosed In this specification (Including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (11)

1. Valve means for connection to a first fluid source and to a second, higher pressure, fluid source, the valve means belng such that when it is subjected to fluid pressure above a first pre-determined level, It supplies fluid from the first fluid source and when it is subJected to a fluid pressure above a second, higher, pre-determined level, the valve means supplies fluid from the second fluid source.

2. Valve means as claimed In Claim 1, connected to a supply conduit which, in use, is provided with fluid, for example, from under the control of a dead man's handle, along a first fluid path, the valve means being such that when the said first pressure level is exceeded, the valve allows fluid to flow from the first source along a second fluid path to said conduit, and when said second pressure level is exceeded, the valve means allows fluid to flow from the higher pressure source along a third fluid path to sald conduit.

3. Valve means as claimed in Claim 1 or Claim 2, such that when in use relatively low pressure fluid is fed via a non-return valve to the sald conduit, when the first pressure level is exceeded a first control valve is opened allowing additional fluid from the same low pressure source to flow Into the said conduit via a second non-return valve, and when the combined flow exceeds the second pressure level a second control valve Is opened when allows higher pressure fluid to enter the conduit and close the non-return valves whereby a third pre-determined pressure in the conduit may be obtalned.

4. Valve means as claimed In Claim 3, in which the conduit comprises the feed line into a hydraulic supporting Jack of a mine roof support, and the low and higher pressure fluid sources comprise the main low pressure and high pressure feed lines from a pumping station located at the end of a longwall mining face, supplying pressure fluid to each support of an Installation.

5. Valve means as claimed in Clalm 4, such that the first control valve, once opened, remalns open until the final pressure in the supporting Jack has been attained, and the second control valve, once opened, remains open for the same duration.

6. Valve means as claimed In any one of the Claims 3 to 5, In which the second control valve is of a pilot operated form.

7. Valve means as claimed in any one of Claims 3 to 6, In which the second control valve embodies two nonreturn valves and a restriction means.

8. Valve means as claimed In Claim 7, in which the second valve Is arranged so that low pressure fluid passes through one of sald non-return valves and higher pressure fluid passes through the outer non-return valve.

9. Valve means constructed and arranged substantially as herein descrlbed with reference to the accompanying drawings.

10. A hydraulic mine roof support fitted with a valve means as claimed in any one of the preceding Claims.

11. A hydraulic mine roof support as claimed in Clalm 10, in which the valve means is arranged to feed fluid to all the supporting jacks of the mine roof support simultaneously.