GB2214235A

GB2214235A - Fluid operated jack

Info

Publication number: GB2214235A
Application number: GB8800443A
Authority: GB
Inventors: Derek Alker; Reginald Andrew Phillips
Original assignee: Gullick Dobson Ltd
Current assignee: Gullick Dobson Ltd
Priority date: 1988-01-09
Filing date: 1988-01-09
Publication date: 1989-08-31
Anticipated expiration: 2008-01-09
Also published as: GB8800443D0; GB2214235B; AU621077B2; AU2766388A

Abstract

A fluid operated jack comprises a piston rod 21 and a co-operating cylinder 24. Sensing means 54, connected to the piston rod externally of the cylinder is provided for sensing when the cylinder reaches a pre-determined position with respect to the piston rod, and actuating means 38, 46, 48 are provided within the cylinder for actuating the sensing means 54. The sensing means may be a balanced valve connected to an electrical signalling device 54 or a pilot valve. The actuating means includes a toggle lever 39 mounted on the piston rod for pivotable movement by a sleeve 40 when, at full extension, the sleeve strikes the cylinder end 27. Movement of the lever 39 displaces a rod 46 and a wedge 48 to operate the sensing means. The jack may for example be used to operate a hydraulic mine roof support, the piston being fixed with respect to the support and the cylinder being movable. The invention makes it possible to receive signals related to the position of the cylinder, with respect to the piston rod, without using hydraulic hoses or other connections which move with respect to the cylinder and would therefore be susceptable to damage. <IMAGE>

Description

FLUID OPERATED JACKS The Invention relations to fluid operated Jacks, for example to the hydraulic jacks of hydraulic mine roof supports.

A hydraulic mine roof support typically comprises a plurality of hydraulic jacks housed between a mine floor engaging base and a mine roof engaging canopy.

Some of the jacks are used to support the mine roof via the canopy, while at least one substantlally horizontal Jack, housed in the lower part of the support, is used to advance the support after the removal of mineral, for example, coai, from the mineral bearlng mine face.

A typical sequence of operations, common to most hydraulic mine roof supports of the type described above, Is as follows : (a) Advance a mineral carrying conveyor positioned In front of a row of supports, by means of the substantially horizontal Jack extending from each roof support and connected to the conveyor.

(b) Lower the canopy of the roof support from contact with the roof by retracting the supporting Jacks.

(c) Advance the roof support by means of the horizontal Jack, using the conveyor as an anchorage.

(d) Set the roof support to the roof once again by extending the supporting Jacks to raise the canopy.

The substantially horizontal Jack may be arranged to advance the conveyor by either extending or retracting the horizontal jack. In the latter condition, the Jack Is generally referred to as a reverse mounted Jack, extension of the jack closing the roof. support up to the conveyor and retraction of the Jack moving the support and the conveyor apart. In practice this results in the piston rod being pivotally attached to the base of the support and so the cylinder of the Jack moves relative to the base of the support.This means that by extending the jack the large, circular area of the advancing Jack is used during the heavier task of advancing the support, whilst by retracting the Jack the smaller annular, area of the Jack is utilised to advance the conveyor, which needs less force, since usually the jacks of several supports are used in unison along the length of the mine conveyor.

In more advanced control systems for mine roof supports, operations (c) and (d) above may be interrelated such that extension of the supporting Jacks Is initlated automatically from the advancing Jack completing its working stroke. In conventionaliy mounted advancing jacks, where the cylinder is attached to and does not move relative to the base of the support, a striker valve may be mounted In the blank end of the jack cylinder, with an actuating stem of the valve projecting Into the cylinder. Once the piston has been fully retracted, a complimentary part of the piston comes into contact with the actuating stem, moving the actuating stem. This movement in turn opens the striker valve of the advancing jack to allow fluid to be fed to the supporting Jacks until such times as they are set to the mine roof.

This arrangement Is widely accepted for mine use, having the advantage that there are no moving hoses feeding fluid into the advancing Jack or to the striker valve which might become entangled during the movement of the roof support toward the conveyor. However in reverse mounted Jacks, the cylinder moves with respect to the base, and If hoses are attached to the cylinder, or the striker valve there is a high risk of entanglement during movement of the cylinder.

As far as the feed hoses are concerned for the supply of fluid to the Jack, it has been shown to be practical to avoid connection of these hoses to the cylinder. Instead, the feed hoses are connected to the piston rod and passages are provided within the piston rod to enable fluid to be fed through the piston rod to each side of the piston of the Jack. Since the exposed end of the piston rod is fixed relative to the support base, the problems associated with moving operating fluid hoses is readily avoidable. However the conventional striker valve Is mounted on the moving cylinder itself and therefore hoses connected to the striker valve must move with the cylinder and hence may become entangled.

The invention seeks to avoid or reduce this problem.

One known solution to the problem involves mounting a complete striker valve assembly in the piston head of the advancing Jack. This method Is complex, because of the need to provide additional feed and return ports through the piston rod. It is also difficult to gain access for maintenance, because It Is necessary to dismantle the jack, an operation which becomes a major task with the limited available working space underground and the need to prevent the ingress of dirt during such an operatlon. Furthermore, additional problems may arise with a striker valve which encroaches Into the working volumes of a hydraulic Jack as It may be sensitive to the jack operating fluid pressure, which could inadvertently open the striker valve before the required extension or retractlon has been achieved.

The Invention seeks to provide a more effective arrangement which removes or al leviates the above mentioned problems.

The invention provides a fluid operated Jack providing a piston and a co-operating cylinder, sensing means connected to the piston, externally of the cyl Inder, for sensing when the cylinder reaches a predetermined position with respect to the piston, and actuating means within the cylinder for actuating said sensing means.

The fluid operated Jack may comprise a hydraulic Jack for a mine roof support.

The actuating means may comprise generating means for generating a signal when the cylinder reaches a predetermined position with respect to the piston, and transmitting means for transmitting the signal from the generating means to the sensing means.

The sensing means may have receiving means for receiving the signal from the transmitting means.

The actuating means may be arranged to operate when the cylinder reaches its fully extended position with respect to the piston.

Preferably the generating means is remote from the sensing means.

The generating means may be positioned in the end region of the piston lying within the cylinder.

The generating means may comprise a striker member attached to the piston, which striker member is struck by a part of the cylinder when the cylinder reaches the pre-determined position with respect to the piston.

The transmitting means may comprise an elongate member extending between the striker member and the sensing means.

The elongate member may extend within the piston.

The receiving means may comprise a member on the sensing means which co-operates with the elongate member.

Preferably the means within the jack, in contact with the operating fluid, is biased to a neutral position by the pressurized fluld, thus preventing the pressurized fluid from affecting the operation of the means.

Preferably means are provided for causing or permitting the striker member to return to its Inoperative position when the Jack commences its return stroke.

The Invention includes a mine roof support having a fluid operated jack according to the invention.

By way of example, a specific embodiment of the invention will now be described, with reference to the accompanying drawings, in which Figure 1 Is a side view of a hydraulic mine roof support, fitted with a reverse mounted hydraulic Jack according to an embodiment of the Invent Ion; Figure 2 Is a cross-sectional view of the Jack according to the embodiment of the Invention; Figure 3 Is a plan view of one end of the hydraulic jack; Figure 4 is an end view of the hydraulic jack; Figure 5 is a transverse cross-section through the Jack, showing the striker member; and Figure 6 is a scrap plan view of part of the Jack, with the sensing means removed.

The hydraulic mine roof support shown in Figure 1 is generally conventional, having a roof engaging canopy 10, a floor engaging base 11, and hydraulic Jacks 12 extending between the canopy and the base, for use in supporting a mine roof. The canopy and base are also Interconnected In a conventional manner by a rear shleld 13 and links 14 and 15.

Lying In front of the mine roof support Is a mine conveyor 16 along which a mining machine 17 is mounted to travel. Extending from the conveyor 16, towards the mine roof support, is a rigid relay bar 18. The bar 18 is connected to the conveyor in a pivotal manner by means of a clevis 19.

The mine roof support differs from conventional supports in that it is provided with a reverse mounted hydraulic Jack 20 according to the invention. The piston rod 21 of the jack is attached to the roof support at 22 and so Is substantially fixed with respect to the base 11 of the roof support. The right hand end of the relay bar 18, as viewed In Figure 1, Is pivotally connected at 23 to the cylinder 24 of the jack 20.

When it Is desired to move the mine roof support forwardly, i.e., towards the conveyor 16, the jack 20 is extended. During the extension stroke, the full bore of the cylinder is available.

After the mine roof support has been moved to its new position and reset to engage the mine roof, the conveyor 16 can be moved forwardly to a new position by actuating the Jacks 20 of a number of supports. During this retraction stroke of the jack, only the annular bore of the cylinder is available, around the piston rod, but less force is required to move the conveyor than to move the mine roof support. In other words, the reverse mounting of the Jack ensures that the maximum force is available for the maJor task, i.e., that of moving the mine roof support.

Once the jack has been fully extended, and the mine roof support has reached its new position, it is desirable to be able to signal 'the upwardly extending Jacks 12 to extend automatically to reset the canopy 10 to the mine roof. This signaling is brought about by the hydraulic Jack 2 according to the invention which will now be described in more detail, with respect to the remaining figures.

The cylinder 24 has a blank end cap 25 at one end and a flange 26 at its other end. The flange 26 provides a strengthened part for retaining an end guIde 27, by means of a threaded part 28 and a locking screw 29. The end guide 27 has an external seal at 30 and an internal seal at 31. The guide 25 also has low frlction bearings 32 for the piston rod 21.

The piston rod 21 has a piston sealIng member 33 which is held In place by a first retaining member 34 at the full bore side with a low frictlon bearing 35. There is also a second retaining member 36 on the annular side, which member 36 is located by a peg 37 which aligns a slotted part 38 relative to the piston rod 21.

A striker member In the form of a toggle 39 is loosely mounted in the piston rod 21 in the region of the retaining member 36, the outer part of the toggle 39 locating In the slotted part 38. The limit of the extension of the Jack Is determined by the length of a slidable sleeve 40 which Is positioned around the piston rod 21. The length of this sleeve Is chosen in dependence upon the desired maximum travel of the Jack.

A first fluid passage Is provided at -41 for extending the Jack and a further fluid passage Is provided at 42 for retracting the Jack. These fluid passages have hose connectlons 43 and 44 respectively for connecting to pressure hoses (not shown).

As can be seen from Figure 4, the passages 41 and 42 extend through the piston rod. Also extending through the piston rod is a guide passage 45 into which is fitted a push rod 46. The passage 45 is sealed by a plug 47 which prevents fluid passing freely from one side of the sealing member 33 to the other.

At the end of the push rod 46, remote from the toggle 39, there is a wedge shaped slipper 48, which is maintalned in contact with the push rod by a plunger 49 and compression spring 50.

Mounted on the piston rod 21, externally of the cylinder 24, is a balanced valve 51 having a plunger 52 in contact with the sllpper 48. Balancing fluid Is fed from the passage 42 via a bleed port 53 Into the valve 51. in use the valve 51 may be connected to an electrical signaling device 54 or connected to a pilot valve (not shown) to generate either an electrical or a hydraulic signal upon actuation of the balanced valve 51.

When the roof support Is to be advanced, fluid pressure is fed to the full bore extend side of the jack 20 via a hose connection 43 and the passage 41 and the jack extends until the sleeve 40 abuts the end guide 27.

The action of these two parts meeting turns the toggle 39 In the clockwise direction as viewed in Figure 2.

Consequently the lower part of the toggle 39 pushes the rod 46 to the left, so that the wedge shaped slipper 48 lifts the plunger 52 of the balanced valve .51 and operates the signaling device 54. The signaling device 54 may transmit the signal to a remote location, for example, to a control unit, (not shown) which brings about actuation of the upwardly extending hydraulic Jacks 12.

When the Jack 20 is subsequently retracted to advance the conveyor, the sleeve 40 moves away from the end guide 27 and pressure on the toggle 39 from the sleeve 40 is relieved. The spring loaded plunger 49 is therefore able to return the slipper 48, rod 46, and toggle 39 to the positions shown in Figure 2.

Because of the Internal actuating devices provided within the Jack, it is possible to mount the valve 51 on the stationary, exposed part of the piston 21. Thus the valve does not intrude Into the working spaces of the Jack, the valve is readily accessible for maintenance, and hose connections to the valve can readily be made. The hose connections do not move with respect to the mine roof support, and this reduces the risk that the hoses will become entangled.

The invention is not restricted to the details of the foregoing embodiment. For example, the mechanical toggle 39 may be replaced by an electrical switch. There may be electrical connections between the switch and the signaling device 54.

Alternatively, there may be a different form of mechanical signaling device between the toggle 39 and the valve 51. For example a Bowden cable may be used.

One of the passages 41 or 42 might be eliminated, being replaced by a modification to the gulde passage 45 which allows an Increased flow of fluid tofthe respective side of the piston seal 33.

Claims

1. A fluid operated jack comprising a piston having a piston rod, and a co-operating cylinder, sensing means connected to the piston rod, externally of the cyllnder, for sensing when the cylinder reaches a pre-determined position with respect to the piston, and actuating means within the cylinder for actuating said sensing means.

2. A fluid operated Jack as claimed In Claim 1, comprising a hydraulic Jack for a mine roof support.

3. A fluid operated Jack as claimed in Claim 1 or Claim 2, in which the actuating means comprise generating means for generating a signal when the cylinder reaches a pre-determined position with respect to the piston, and transmitting means for transmitting the signal from the generating means to the sensing means.

4. A fluid operated Jack as claimed in Claim 3, in which the sensing means has receiving means for receiving the signal from the transmitting means.

5. A fluid operated Jack as claimed in Claim 4, in which the actuating means is arranged to operate when the cylinder reaches Its fully extended position with respect to the piston.

6. A fluid operated Jack as claimed in Claim 4 or Claim 5, In which the generating means is remote from the sensing means.

7. A fluid operated Jack as claimed in Claim 6, in which the generating means is positioned in the end reglon of the piston lying within the cylinder.

8. A fluid operated jack as claimed in Claim 7, in which the generating means comprises a striker member attached to the piston, which striker member is struck by a part of the cylinder when the cylinder reaches the pre-determined position with respect to the piston.

9. A fluid operated Jack as claimed In Claim 8, in which the transmitting means comprises an elongate member extending between the striker member and the sensing means.

10. A fluid operated jack as claimed In Claim 9, In which the elongate member extends within the piston.

11. A fluid operated Jack as claimed In Claim 10, in which the receiving means comprlses a member on the sensing means which co-operates with the elongate member.

12. A fluid operated Jack as claimed In any one of Claims 8 to 11, In which the means within the Jack, in contact with the operating fluid, is biased to a neutral position by the pressurized fluid, thus preventing the pressurized fluid from affecting the operating of the means.

13. A fluid operated Jack as claimed, in any one of Clalms 8 to 12, In which means are provided for causing or permitting the striker member to return to its inoperative position when the Jack commences its return stroke.

14. A fluid operated Jack, constructed and arranged substantlally as herein described, with reference to the accompanying drawings.

15. A mine roof support having a fluid operated jack as claimed in any one of the preceding Claims.

16. A mine roof support as claimed in Claim 15, connected to an abutment such as a conveyor by the fluid operated Jack, the piston rod being attached to the support and the cylinder being connected to the conveyor such that when the Jack is extended, with fluid pressure applied across the entire working area of the piston, the support is moved towards the conveyor.

Amendments to the claims have been filed as follows 1. A fluid operated jack comprising a piston assembly In the form of a piston having a piston rod, and a co-operating cylinder said piston assembly having sensing means connected to the piston rod, externally of the cylinder, for sensing when the cylinder reaches a pre-determined position with respect to the piston, and actuating means connected to the piston assembly within the cylinder for actuating said sensing means.

2. A fluid operated Jack as claimed in Claim 1 In which the cylinder has unobstructed inner pressure surfaces.

3. A fluid operated Jack as claimed in Claim 1 or Claim 2 comprising a hydraulic Jack for a mine roof support.

4. A fluid operated Jack as claimed In any of the preceding Claims, In which the actuating means comprise generating means for generating a signal when the cylinder reaches a predetermined position with respect to the piston, and transmitting means for transmitting the signal from the generating means to the sensing means.

5. A fluid operated Jack as claimed in Claim 4, in which the sensing means has recelving means for receiving the signal from the transmitting means.

6. A fluid operated jack as claimed in Claim 5, in which the actuating means is arranged to operate when the cylinder reaches its fully extended position with respect to the piston.

7. A fluid operated Jack as claimed in Claim 5 or Claim 6, In which the generating means is remote from the sensing means.

8. A fluid operated Jack as claimed in Claim 7, in which the generating means is positioned In the end region of the piston lying within the cylinder.

9. A fluid operated jack as claimed in Claim 8, In which the generating means comprises a striker member attached to the piston, which striker member is struck by a part of the cylinder when the cylinder reaches the pre-determined position with respect to the piston.

10. A fluid operated Jack as claimed in Claim 9, in which the transmitting means comprises an elongate member extending between the striker member and the sensing means.

11. A fluid operated Jack as claimed in Claim 10, in which the elongate member extends within the piston.

12. A fluid operated Jack as claimed in Claim 11, in which the receiving means comprises a member on the sensing means which co-operates with the elongate member.

13. A fluid operated Jack as claimed in any one of Claims 9 to 12, in which the means within the Jack, in contact with the operating fluid, is biased to a neutral position by the pressurized fluid, thus preventing the pressurized fluid from affecting the operating of the means.

14. A fluid operated Jack as claimed in any one of Claims 9 to 13, in which means are provided for causing or permitting the striker member to return to its inoperative position when the jack commences its return stroke.

15. A fluid operated Jack, constructed and arranged substantially as herein described, with reference to the accompanying drawings.

16. A mine roof support having a fluid operated Jack as claimed in any one of the preceding Claims.

17. A mine roof support as claimed in Claim 16, connected to an abutment such as a conveyor by the fluid operated Jack, the piston rod being attached to the support and the cylinder being connected to the conveyor such that when the jack is extended, with fluid pressure applied across the entire working area of the piston, the support Is moved towards the conveyor.