GB2047316A - Improvements in hydraulic control apparatus for controlling the operation of mine roof support props - Google Patents

Abstract

Hydraulic control apparatus for mine roof support props includes a manually-operable main valve (11) which can be set to selectively connect fluid pressure and return lines (P, R) to the working chambers (10', 10'') of at least one associated prop (10) to extend and retract the prop. A pressure-relief valve (12) is connected to the chamber (10') which effects extension of the prop. The relief valve (12) is capable of passing the same quantity of fluid as the main valve (11) and operates at a pressure only slightly greater than the setting pressure of the prop. An automatic setting arrangement (15, 24), connects the prop chamber (10') to the pressure line (P) automatically when the chamber pressure rises beyond a threshold level and the prop is in contact with the roof. This ensures that the correct setting pressure is established whether or not the main valve (11) has disconnected the pressure line (P) from the prop chamber (10'). The pressure line is disconnected at a chamber pressure only just below the response pressure of the relief valve (12). In an alternative embodiment the relief valve (12) is automatically set to respond to a significantly higher pressure whilst the prop (10) is actually being set by the main valve (11) and reverts back to its normal response pressure once the prop (10) has been set. <IMAGE>

Description

SPECIFICATION Improvements in hydraulic control apparatus for controlling the operation of mine roof support props The present invention relates to hydraulic control apparatus for operating the support props of a mineral mining installation.

Control apparatus is described in published German patent specification P27 49 31 2.5 which utilizes manual-operable control valves which serve to connect pressure fluid feed and return lines selectively to the working chambers of associated props. The apparatus employs an automatic setting arrangement coniposed of valve devices. This arrangement automatically connects the prop chambers, charged with fluid to extend the props, to the pressure line once a threshold pressure is exceeded. This ensures the props can be properly set against the roof even if one of the control valves is operated prematurely to disconnect the pressure line to an associated prop chamber. The automatic setting arrangement isolates the prop chambers from the pressure line once the setting pressure is reached.Excessive pressure is prevented from building up in the prop chambers by means of pressure-relief valves set to respond at pressure above the normal setting pressure. The threshold pressure level at which the setting arrangement comes into operation is higher than that present in the prop chambers when the props are being extended freely without contact with the roof and less than the setting pressure. The threshold pressure is selected so that any prop can be extended and retracted by operation of the associated control valve freely and the prop can be extended until its roof cap or the like actually contacts the roof without the setting arrangement coming into action. This enables repair and maintenance work, and any back filling nec sssary in the event of roof falls, to be performed without the automatic setting arrangement becoming affected.Generally the threshold pressure at which the setting arrangement comes into operation is in the range 50 bars to 1 50 bars while the pressure in the pressure line is significantly higher-typically above 300 bars and in the range 350 bars to 450 bars.

A general object of the present invention is to provide improved control apparatus for operating the support props of a mining installation and improved valve devices for use in such apparatus.

Control apparatus constructed in accordance with the invention utilizes a manually-operable control valve device which can be set with a lever to various positions to connect the chambers of an associated roof support prop to pressure fluid feed and return lines to effect extension and retraction of the prop in a manner known per se. Preferably the control valve device has the so-called "deadman's handle" mechanism which causes the device to adopt a neutral position when its lever is released to isolate the pressure line from the prop pressure chamber which is used to extend the prop. A pressure-relief valve device is connected to the prop pressure chamber to prevent excessive pressure building up.

As known per se, an automatic setting arrangement can serve to connect the prop chamber to the pressure line once a threshold pressure is exceeded. This arrangement disconnects the pressure line from the pressure chamber once the setting pressure is reached. In accordance with one aspect of the present invention the pressure at which the automatic setting arrangement disconnects the pressure line from the pressure chamber is approximately equal to the response pressure of the pressure-relief valve device and preferably is just less than this response pressure. The pressure at which the automatic setting arrangement disconnects the pressure line from the prop pressure chamber is preferably not more than 10% lower and expediently 5% less than the response pressure of the relief valve device.In addition the pressurerelief valve device is designed to pass the maximum possible throughflow quantity of pressure fluid which is approximately the same as that passed through the main control valve device while the prop is being extended. This development permits the props to be set with a force in the range of their full rated loading without the possibility of damage to the relief valve devices. To achieve the high setting force, the working pressure in the pressure fluid feed line must be correspondingly high to take account of unavoidable pressure drops and fluctuations. The working pressure is preferably somewhat higher than the setting pressure.Because of pressure fluctuations which occur the pressure prevailing at the onset of the setting operation effected by the manual actuation of the main control device can easily reach a peak value which causes the associated pressure-relief valve device to respond.

However, by making the latter valve device pass a higher quantity of pressure fluid than is normal and at least the same as that passing through the control valve device the entire quantity of fluid passed through the control valve device can be conveyed away safely by the relief valve device until the prevailing pressure falls back below the response pressure. A pressure-relief valve suitable for this task can be based on that described in German published Patent Specifications 1 750834 and 2803283. However the internal fluid flow cross-section of the valve must be increased to permit the aforesaid larger throughflow characteristics.

In another aspect of the invention the pressurerelief valve device is modified in a different respect. In this case pressure control can be established to make the response pressure of the relief valve device significantly higher while the setting operation takes place. The pressure control can effect this change automatically so the valve device only responds during setting if an especially- high pressure peak occurs. Once the associated prop has become set however, the pressure control permits the relief valve device to revert back to its normal response pressure. With this pressure control it is not necessary to make the relief valve device pass the higher quantity of fluid discussed hereinbefore.The pressure relief valve device with the pressure control facility can employ a spring-loaded piston member siiding in a guide piece provided with a mating O-ring seal. A housing, accomodating the guide piece and its piston member, may have a chamber which is connected to the pressure line when the prop is being set. The -esulting pressure in the housing chamber can then supplement the spring force holding the piston member in a closure position.

Once the setting operation has been terminated the housing chamber is relieved of pressure so the response pressure is determined solely by the spring force. Where the apparatus employs a relief valve device subject to the pressure control as describea, it is possible to omit the automatic setting arrangement if desired. The invention may be understood more readily, and various other aspects and features of the invention may become apparent, from consideration of the following description.

Embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings, wherein Figure 1 is a schematic representation of hydraulic control apparatus constructed in accordance with the invention, and Figure 2 is a schematic representation of another hydraulic control apparatus constructed in accordance with the invention.

As shown in Figure 1, control apparatus has a setting valve device 11 connected by way of example through conduits or lines 13, 14 to the working chambers 10', 10" of an hydraulic prop 10 and to pressure fluid feed and return lines P, R.

It is also possible to connect the valve device 11 to several props instead of a single prop as shown.

The valve device 11 is capable of adopting one of three settings or states depicted schematically in the drawing. The valve device 11 preferably has a housing with flat surfaces for face-to-face mounting at some convenient location and employs a rotary slide valve actuated by a pivotable control lever accessible at the exterior of the housing. The valve device 11 is provided with an automatic return mechanism -the so-called 'dead man's handle' - which automatically brings the control lever back to a neutral position when released. This neutral position corresponds to a neutral state or setting designated 0 and shown to be adopted in Figure 1. In the state 0, the device 11 connects the chamber 10" to the return line R while isolating the chamber 10' from the pressure line P.With the valve device 11 set to the control state designated 1, the chamber 10' is connected to the pressure feed line P while the chamber 1 OR is connected to the return line R. This setting state 1 initiates extension and setting of the prop 1 0.

With the valve device 11 set to the control state designated 2, the chamber 10' is connected to the return line R while the chamber 10" is connected to the pressure feed line P. This setting state 2 initiates positive retraction of the prop 1. With the device 11 set to the active states 1 or 2, the typical flow rate of pressure fluid through the device 11 is 50 litres per minute at a typical working pressure in the feed line P of about 400 bars. In practice, the pressure in the feed line fluctuates from time to time and changing the valve device 11 to the setting state 1 does not always ensure that the prop or props associated therewith will become set in roof contact with a setting pressure corresponding to their proper full rated loading.A pressure-relief valve device 1 2 is connected to the line 13 leading to the chamber 10' and hence to the chamber 10' of the prop 10.

The device 1 2 is also connected to the fluid return R. The device 1 2 is set to open at a response pressure approximately corresponding to the rated loading-typically 370 bars. Thus, when this pressure is established in the chamber 10', after the valve device 11 has been set to state 1, the device 12 opens to preclude any pressure rise due to surges and closes once the pressure falls again.

The valve device 12 is also capable of passing high quantities of fluid therethrough -- preferably at least the flow rate of the valve device 11 i.e. at 50 litres per minute. Hence, if when the valve device 11 is set to state 1, the pressure in the feed line P is above the response setting of the valve device 12 then the valve device 12 will respond instantly. The valve device 12 will open so the entire quantity of fluid flowing through the device 11 to the conduit 13 will be drawn off through the device 12 to return. This prevents any possibility of pressure building up in the chamber 10' above the setting response pressure of the device 12.

Once the pressure falls below the response setting of the device 12, the device 12 will close permitting the fluid to pass through the device 11 to charge the chamber 10'.

By constructing the valve device 12 so it can pass relatively high quantities of pressure fluid, commensurate with the device 11 and unlike conventional pressure-relief valve devices, damage and rapid wear of the device 12 can be prevented. The valve device 12 can be constructed in a manner known per se.

The device 12 may thus have a spring-loaded piston member slidably mounted in a guide bore of a guide piece provided with an O-ring seal engaging on the shank of the piston member. The piston member has an axial bore leading through radial bores which open into fluid outlets at the exterior surfaces of the shank. The guide piece with the associated piston member are retained in a housing containing the spring which bears on the piston member via a thrust plate to hold the piston member in a position with its outlets closed by the O-ring seal. As the pressure of fluid acting on the piston member rises above a predetermined level the piston member moves in the guide bore to bring the outlets passed the O-ring seal to permit fluid discharge. With the piston member displaced to open the valve the fluid path cross-section is sufficiently large to permit the necessarily-large flow rates discussed above.

The control apparatus also employs automatic setting means. This means includes a further setting valve device 1 5 which can adopt one of two states designated a and b. The device 1 5 is connected at an inlet to a conduit or line 1 6 leading to the pressure line P and at an outlet to a conduit or line 17 leading to the line 13 and thence to the prop working chamber 10'. A nonreturn valve 1 8 is incorporated in the line 17. In setting state a the line 1 7 is isolated from the pressure fluid feed line P while in the setting state b the line 1 7 is connected to the pressure line P.

Unlike the device 11, the device 1 5 is solely pressure-actuated. As illustrated in Figure 1, the device 1 5 has a control piston 1 9 connected through a conduit or line 20 with the line 17, downstream of the valve 18, and thence with the line 13. The device 1 5 also has a second control piston 21 with a larger working area than the piston 1 9. The piston 21, which opposes the action of the piston 19, is connected through a conduit or line 22, and a conduit or line 25 containing a non-return valve 26 to the line 17 downstream of the valve 18. A pressure-relief valve device 24 has its inlet connected to the line 1 7 to lead directly to the line 13 and hence the prop working chamber 10'.The device 24 has its outlet connected to the line 22 and directly to the piston 21. The response pressure of the relief valve device 24 is equal to or slightly less than that of the device 12. Typically where the device 12 is set to open at 370 bars the device 24 would be set to open at around 360 bars. With both pistons 1 9, 21 of the device 1 5 exposed to the same pressure the piston 21 will prevail because of its larger area and the device 1 5 will adopt the state a. State a is also the normal non-functioning state of the device 1 5 when neither piston 19, 21 is exposed to pressure or when the piston 1 9 is exposed to pressure below a set threshold. Only when the piston 1 9 solely is exposed to pressure above the set threshold will the device change from state a to b.

Assume that the prop 10 is retracted as illustrated in Figure 1. In order to extend and set the prop 10 the device 11 is set to state 1 by moving its control level. So long as the roofengaging part of the prop 10 or its roof bar does not contact the roof of the working the pressure which builds up in the chamber 10' is determined essentially by the resistance to extension of the prop and the weight of its roofbar and is relatively low-typically 50 bars or less. When the roofengaging part of the prop 10 or its roof bar actually contacts the roof the pressure in the chamber 10' rises towards the pressure in the line P so long as the device 12 remains closed and so long as the device 11 remains in the setting state 1.If the device 11 is changed from state 1 prematurely however the pressure in the chamber 10' may be considerably lower than the ideal setting pressure which can be extremely dangerous. The automatic setting means or arrangement enclosed by chain-dotted lines in Figure 1 is designed to prevent this from happening. The automatic setting arrangement is designed to come into operation at a predetermined pressure threshold value -- typically above 50 bars and below 1 50 bars e.g. 120 bars.

As soon as this pressure threshold value prevails in the chamber 10', signifying the prop 10 has been extended to contact the roof and is not extending or retracting freely, the piston 1 9 acts to change the device 1 5 from state a to state b automatically. This results in the chamber 10' being connected to the pressure line P via the device 1 5 and the lines 13, 17 effectively bypassing the device 11. Hence any premature change of the device 11 will not affect the correct setting of the prop 10 and if the device 11 is maintained in state 1 as would be normal the devices 11, 1 5 act in parallel to charge the chamber 10' to the desired setting pressure.

Whether the device 1 5 is passing fluid to the chamber 10' singly or in combination with the device 11 when the pressure in the chamber 10' reaches the response pressure of the relief device 24, e.g. 360 bars, the latter will open. The opening of the device 24 causes the piston 21 of the valve device 1 5 to become exposed to pressure and the piston 21 prevails over the piston 19 to change the device 1 5 back to state a thereby breaking the path from the line P through the device 1 5 to the chamber 10'.

In the alternative embodiment depicted in Figure 2, the automatic setting arrangement is omitted while the relief-valve device is modified to have pressure control. For convenience, like reference numerals denotes like parts '.D Figure 1.

In Figure 2, the pressure-relief valve device 12 is shown as composed of a guide 32 screwed into the open end of a cylindrical housing 33 and a piston or valve member 30 guided for sliding in main bore 31 of the guide 32. The housing 33, contains a spring 34 which bears on the inner end wall of the housing 33 and on a pressure plate 35 engaging on a domed head 36 of the valve member 30. The bore 31 of the guide 32 leads through a conduit or line 37 to the conduit or line 1 3 connected to the prop working chamber 10'.

An O-ring seal 38 is contained in a groove in the wall of the bore 31 and seals to the exterior periphery of a stem of the valve member 30. This stem contains an axial bore and radial borings open to the periphery and can be raised to bring the radial borings above the seal 38 to permit fluid to pass into the housing 33. The interior 39 of the housing 33, is connected through a passage 40 in the guide 32 to an annular chamber 41 which in turn is connected through a conduit or line 42 to the conduit or line 13. A non-return valve 43 is incorporated in the line 1 3 between the junctions with the lines 37, 42. As with the embodiment shown in Figure 1, the device 12 can be set to respond normally at 370 bars. If the setting valve 11 is set to state 1, the chamber 10' is connected to the pressure line P and the prop 10 extends.

The pressure prevailing in the line 13 leading to the chamber 10' is transmitted through line 42, the chamber 41 and the passage 40 into the chamber 39 and hence acts with the spring 34 to hold the valve member 30 in a closed position.

The pressure in the line 13 is also transmitted through the line 37 to the borings in the valve member 30 but the valve member 30 cannot become raised to open the valve because of the additive spring and pressure force acting in the opposite closing.direction. Hence, when the prop 10 is being extended and set the device 1 2 cannot open unless a particularly high pressure prevails.

When the prop 10 has become set and the device 11 is set back to its neutral state 0 the chamber 39 becomes connected via the passage 40 and the line 42 to the return line. Consequently, the chamber 39 is relieved and only the closure force of the spring 34 acts on the valve member 30.

Consequently should the pressure in the chamber 10' rise beyond the response setting of the device 12 the value member 30 will rise to allow pressure relief. The change over to permit the valve device 12 to function is achieved automatically whenever the device 11 adopts its neutral state.

Although the automatic resetting arrangement of Figure 1 is omitted in the Figure 2 embodiment this is merely iilustrative and the arrangement can be incorporated in the figure 2 apparatus as well if desired.

Claims (8)

1. Hydraulic control apparatus for controlling the operation of mine roof support props; said apparatus comprising a control valve device for selectively connecting first and second working chambers of an associated support prop to pressure fluid feed and return lines to effect extension and retraction of the props, a pressurerelief valve device connected to the first working chamber of the prop which is charged with pressure fluid by the control valve device when the prop is to be extended and set and automatic setting means for connecting said first working chamber to t e pressure fluid feed line independently of the control valve device when a pre-determined threshold pressure is exceeded therein signifying that the prop is being set and for disconnecting said first working chamber from the pressure fluid feed line when a desired setting pressure is reached; wherein the pressure at which the automatic means disconnects the first working chamber from the pressure fluid feed line is just lower than the response pressure of the relief-valve device and the relief-valve device is designed to pass a maximum throughflow quantity of pressure fluid at least the same as the maximum through-fiow quantity of fluid passed through the control valve device during extension and setting of the prop.

2. Apparatus according to claim 1, wherein the pressure at which the automatic means disconnects the first working chamber from the pressure fluid feed line is not more than 10% lower than the response pressure of the relief valve device.

3. Apparatus according to claim 1, wherein the pressure at which the automatic means disconnects the first working chamber from the pressure fluid feed line is not more than 5% lower than the response pressure of the relief valve device.

4. Hydraulic control apparatus for controlling the operation of mine roof support props; said apparatus comprising a control valve device for selectively connecting first and second working chambers of an associated support prop to pressure fluid feed and return lines to effect extension and retraction of the props and a pressure-relief valve device which is connected to the first working chamber of the prop which is charged with pressure fluid by the control valve device when the prop is to be extended and set and control means which automatically changes the response pressure of the relief valve device so that the response pressure of the relief-valve device is higher when the associated prop is being extended and set than it is when the prop has become set.

5. Apparatus according to claim 4, wherein the pressure relief valve device has a spring-loaded piston member slidably mounted in a guide piece having an O-ring seal mating with the piston member and a housing containing a chamber locating the guide piece and the piston member, the control means serving to connect the chamber in the housing to the pressure line when the prop is being extended and set so that the closure force exerted on the piston member by the spring is supplemented by the pressure in the chamber.

6. A hydraulic control apparatus for controlling a pressure-fluid operated roof support prop of mining apparatus; said apparatus comprising: a) main pressure fluid feed and return lines; b) a manually-operable control device for selectively connecting the feed and return lines to working chambers of the prop to effect extension and retraction thereof; c) a setting valve device connected to a first working chambers of the prop which is charged with fluid to effect extension of the prop and to the pressure line, said valve device being settable to a first state where connection is established between said working chamber and the pressure line or a second state, where connection is broken between the pressure line and said working chamber;; d) a first control piston of the valve device for causing the valve device to adopt said first state when exposed to pressure above a threshold level signifying the prop is being set.

e) a pressure-relief valve device connected to said working chamber to respond and open at a pressure signifying setting of the prop has been effected.

f) a further control piston of the setting valve device connected to the pressure-relief valve device to cause the setting valve device to adopt the second state when the setting pressure has been established in said working chamber and g) a second pressure-relief valve device connected to the working chamber of the prop, the second relief valve device being set to respond and open to relieve pressure in the working chamber of the prop at a response pressure slightly greater than that at which the first pressure-relief valve device responds and the second relief valve device serving to pass a maximum pressure fluid quantity when opened at least equal to that passed by the control device when the latter connects the pressure line to the working chamber of the prop.

7. Hydraulic control apparatus for controlling a pressure-fluid operated roof support prop of mining apparatus; said apparatus comprising: main pressure fluid feed and return lines, a manually-operable control device for selectively connecting the feed and return lines to working chambers of the prop to effect extension and retraction thereof, a pressure-relief valve device having a piston member with relief borings slidably mounted in a guide piece provided with an O-ring seal engaging on the piston member, a housing locating the guide piece and the piston member, a spring in the housing acting on the piston member to hold the latter in a position with the valve device closed, a fluid connection between the relief borings of the piston member and the particular working chamber of the prop which is charged with pressure fluid to effect extension and setting of the prop, the piston member being movable by excessive pressure above a response pressure set by the spring to open the valve device and a further fluid connection leading to the chamber in the housing to expose the chamber to pressure to supplement the spring closure force and make the response pressure significantly higher when the control device connects the working chamber of the prop to the pressure line.

8. Apparatus substantially as described with reference to, and as illustrated in Figures 1 or 2 of the accompanying drawings.