TEMPORARY VENTILATION SYSTEM FOR MINING OR TUNNELLING BACKGROUND OF THE INVENTION This invention relates to a ventilation system for use in the digging of underground passages such as mines and tunnels. It can be particularly advantageous when adapted for use in so-called high-wall mining by which following a strip-mining operation which has left exposed unremoved overburden a near vertical face of unremoved seam or stratum, the remaining seam is mined for its constituent material usually coal. A high-wall mining operation consists of digging into the seam through its exposed face in a generally horizontal to dipping direction and extracting the seam material as an aggregate.

In one form of the high-wall mining apparatus, a cutting head or other tunnelling device precedes a conveyor system consisting of an endless conveyor belt (which term is used herein to connote also equivalents such as an endless track), or a linked train of such belts, by which the aggregate produced by the cutting head, as it and the following conveyor system advance into the seam, is conveyed out to a collecting location. As can readily be appreciated, a similar form of apparatus could equally be used for the formation of other kinds of generally horizontal or inclined underground passages. Such apparatus may be remote controlled, with no intention of access by personnel and consequently no provision a of ventilation for them. The high-wall mining apparatus is frequently provided with a launch vehicle which is placed at the tunnel mouth at the base of the high-wall. It serves as a platform to connect the vehicles holding the linked train of endless conveyor belts and to push and pull the linked mining system comprising the cutting head and the conveyor vehicles in and out of the tunnel.

A potential problem in the use of such an apparatus occurs in gassy stratum where gas is emitted and mixed with air in the tunnel to form a potentially explosive mixture which might be ignited by a variety of ignition sources. Such sources may include the cutting picks striking rock, electrical faults or frictional ignition as a result of falling rocks.

Some attempts have been made to prevent such ignitions occurring by rendering the atmosphere in the tunnel unable to by ignited (inert). Such techniques are however fraught with difficulty associated with pumping an inert

atmosphere into the tunnel and sealing the tunnel section to prevent the escape of the inert gas and the ingress of air whilst permitting the access of the mining system to the tunnel. In this event, the air may mix with gas emitted from the stratum to form an explosive mixture. Layering of gasses of different densities increases the difficulties associated with the use of a pumped inert atmosphere.

In one application the inert atmosphere was conveyed to the cutting head by means of a continuous tube stored in a coil from the top of the launch vehicle and unrolled along the length of the tunnelling system. Such a coil could only be of a comparatively small diameter and because of its lightweight construction was subject to damage by falling rocks.

SUMMARY OF THE INVENTION According to the present invention, the passage digging apparatus of the form indicated in additionally provided with a means by which gas (which may include or be entirely air) may be provided to ventilate the tunnel substantially continuously throughout the operation of advance and the withdrawal of the mining system from the tunnel.

According to one aspect, the invention provides a ventilation system for a mining or tunnelling apparatus having a cutting head, or other tunnelling device the system including a plurality of mining vehicles adapted to be connected end to end with a leading or downstream said vehicle being connected to the cutting head, each said vehicle having a conveyor portion and a ventilation duct, a first inlet into the duct adjacent an upstream end of the duct for a ventilation gas with a first closing device for opening and closing the first inlet and a second inlet into the duct adjacent the upstream end thereof with a second closing device for opening and closing the second inlet, the vehicles being connectable end to end so that the ducts may communicate with one another when the second closing device of all of the ducts accept the second closing device of the duct of the upstream vehicle are open and the first closing device of all of the ducts of the vehicles except the closing device of the duct of the upstream vehicle being closed and a feed system for introducing ventilation gas into the first inlet of the duct of the upstream vehicle or for withdrawing gas from the first inlet of the duct of the upstream vehicle.

For this purpose each of the vehicles entering the tunnel is fitted with a ventilation duct which can be interconnected. As these ventilation ducts to not have to flex they can be of substantial size thus permitting large flows for comparatively little pressure drop. The ventilation ducts have two inlets or entries protected by one way check valves and at least one exit at the downstream end. One of the entries is at the upstream end of the duct and is intended to be coupled to the downstream end of the duct on the following mining vehicle (a term herein used to describe the cutting head, conveyor car or other mobile equipment connected to form an interconnected train of equipment used in the excavation of a passage or transport into or from that passage) thus permitting a piece-wise continuous ventilation duct to be formed along the length of the mining system. The interconnection of the ducts is preferably by the use of intemal or external flexible tube couplings so as to permit some relative movement between the mining vehicles. The inlet or entry into the duct permits the introduction of ventilation gas into that duct by the feed system.

Preferably the invention makes use of a feed system having two or more supply tubes carrying gas from a compressor, fan or other such supply device.

During one phase of the cycle one supply tube provides gas to a section of the duct whilst the other is turned off by the use of a valve. During this phase the mining system may progress into the tunnel and an additional mining vehicle can be added to the mining system and its ventilation duct be connected. The next phase of the cycle takes place when the additional mining vehicle has been coupled. In this case the second supply tube can be attached to the duct on this second vehicle via the secondary or other entry and the gas flow diverted from the first supply tube to the second. If a make and break type diversion valve is used no interruption to the supply of ventilation occurs although short durations of loss of ventilation may occur. The final phase of the operation is in the removal of the first supply duct from its secondary or other inlet before that mining vehicle enters the tunnel. The process may continue with a leapfrogging of ducts from one mining vehicle to another.

The extraction of the mining system involves the reverse operation, namely before a mining vehicle is removed from the rear of the mining system, a

supply tube is connected to the duct on the vehicle closer to the mine face, the flow is diverted to that supply tube and then the supply tube to the vehicle being removed is disconnected. The supply tubes are preferentially attached to telescopic or otherwise extendable tubes which permit the supply tubes to move with the mining vehicles.

In an alternate form of the current invention the tubes may be operated in vacuum drawing gas from out of the tunnel and therefore drawing air or gas along the tunnel around the mining system. In this event the check valves or other closing devices are fitted to permit flow only out of the ducts.

Preferably the flexible couplings between the tubes are self energising although this is not essential. By such means in the event of positive pressure within the ventilation ducts the seal is on the inside of the tube and is energies by the internal pressure. Alternatively in the event of a vacuum operation of the ventilation tubes the seal is on the outside and is drawn onto the duct ends by the vacuum to make the seal.

Preferably the closing devices used in the ventilation ducts are of a swing check nature with a low resistance to flow.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example with reference to the drawings in which; Figure 1 shows a view of a typical high-wall mining operation in an open cast mining site and a ventilation system according to an embodiment of the invention; Figure 2 shows typical operation of the ventilation system with positive pressure ventilation ducts on the conveyor cars; Figure 3 shows the ventilation ducts and their feed system incorporating supply tubes and the ancillary valve-work of a typical application ; and Figure 4 shows a form of check valve that would be appropriate for use in the ventilation ducts on the mining vehicles.

DESCRIPTION OF THE DRAWINGS Figure 1 shows a typical high-wall mining operation in an open cast mining site. The ore body being mined (1) is accessed from the base of the high-

wall (2) from the pit floor (3) with poil pile (4) usually behind the workings. The high-wall mining system comprises cutting head (5) behind which are conveyor cars or vehicles (6) which carry conveyors (7) and are coupled using couplings (8). The mining system or train is launched and retrieved from a launch vehicle (9) which shows coupled vehicles and a vehicle (10) which has yet to be coupled.

Figure 2 shows typical operation of the ventilation system with positive pressure ventilation ducts on the conveyor cars or vehicles. Conveyor cars (12a, 12b and 12c) each carry ventilation ducts (14a, 14b and 14c) and conveyors (13). In the figure the ventilation tube (14c) is receiving air or gas which is passing through open check valve or other closing device (19) in an inlet. The other check valves or other closing devices 15a, 15b associated with the inlets as shown are closed thus preventing the escape of gas from the connected ventilation tube. In line check valves or other closing devices (18a and 18b) are open thus permitting fee passage of the ventilating gas. In line check valve or other closing device (18c) is closed by the pressure difference between the inside of the ventilating ducts and atmosphere. A seal (16) interconnects adjacent tubes or ducts.

Figure 3 shows the ventilation ducts and their feed system incorporating supply tubes and the ancillary valve-work of a typical application. For clarity the details of the mining vehicles and launch vehicle have been omitted leaving a view of the ventilation ducts, valves and associated equipment alone. In addition the telescopic tube arrangements (38,39,40,41,42 and 43) are shown vertically staggered for clarity whereas in reality they would be expected to be at the same height, one behind the other. In the drawing (45) is a diversion valve directing gas into the upper telescopic tube arrangement (40) which is actuated to move with the mining vehicle by hydraulic or compressed air driven ram (42) although other forms of extension such as electrically operated screw devices may be used. The air then is carried around the bend in the ducting (38) through a bellows or similar device to permit adjustment of vertical height and lateral alignment of the supply tube (34). This supply tube is connected via a seal (30) which is internally energised by the gas pressure and held by mechanical clamps

(32) to the secondary entry of duct (20) which is attached to the mining vehicle entering the tunnel. The check valve or other closing device (28) to the secondary entry of duct (20) is open and the check valve or other closing device (26) in the in-line part of duct (20) is closed by the differential pressure between the gas in duct (20) and that existing in duct (21) which is shown connected to duct (20) via seal (24) and disconnected from the supply tube (35) and the duct (23) on the mining vehicle about to be attached. When supply tube (35) is connected to the secondary entry on duct (21) using seal (31) and clamps (33) then the flow can be diverted by the diversion valve (45) through the telescopic tube (41), bend (39) bellows (37) and into supply tube (35). In this event check valve or other closing device (29) will open and check valve or other closing device (27) will be forced to close by pressure and gas will begin to flow in duct (21) and through check valve or other closing device (26) into duct (20). At this stage the mechanical clamp (32) can be released and the seal (30) disengaged with a result that check valve or other closing device (28) closes. Ventilation is now fully established through duct (21). The supply tube (35) can be advanced with the mining vehicle to which duct (21) is attached by the use of the telescopic tube (41) controlled by ram (43). The supply tube (34) can be retracted by means of telescopic tube (40) controlled by the ram (42) to link with the secondary inlet to the next vent tube (23).

Figure 4 shows a form of check valve or other closing device that would be suitable for use in the vent ducts used in the invention. The check valve or other closing device is preferably circular in section and consists of two flaps (50 and 51) that can rotate about axles (52 and 53). These flaps may be intemally or externally balanced to neither close nor open when no differential pressure exists across the valve. The flaps bear against sealing extemal restraints (54 and 55) and internal sealing restraints (56 and 57). Figure 4a shows the valve closed as does Figure 4c but through section A-A. In this form flow is resisted by the flaps supported on the sealing restraints and the axles. Figure 4b is a section through A-A in Figure 4a and shows flow through the check valve or other closing device when the flaps (50 and 51) are wide open having rotated about the axles (52 and 53).