GB2470974A - Underground railway tunnel ventilation apparatus - Google Patents

Abstract

The invention provides a railway tunnel ventilation apparatus which significantly enhances the piston effect of an underground train moving a column of air from a single track underground tunnel into a station platform area where it is naturally but indirectly replaced by fresh air from the surface. The apparatus comprises a ventilation car V having the same cross-section as a train carriage 100. An onboard air curtain generator draws air from both ends of the car V and ejects it as continuous air curtains extending in use from the outer periphery of the car V to the tunnel internal surface. The air curtains act as a barrier to air flowing past the car V in the space between the carriage and tunnel, so that the air curtain assists in the driving of a column of air ahead of the train.

Description

TITLE

Underground Railway Tunnel Ventilation for Single Line Tunnels

DESCRIPTION

Field of the Invention

The invention relates to the ventilation of the tunnels and optionally also the train carriages of an underground railway system, particularly a single line deep tunnel system such as parts of the London Underground system and others like it around the world.

Backcround In the London Underground railway system, and others like it, trains travel in single track tunnels between stations. Air is forced through the tunnel network by the piston effect of moving trains, with warmer stale air rising to the surface and being replaced by cooler fresh air both at stations and through ventilation shafts. Air replacement through new ventilation shafts is expensive, the expense arising through the initial cost of excavating those shafts, the real estate value of the land at the surface where the shafts emerge to draw in fresh air, and the possible need to pump that fresh air down the shafts. Air replacement at the stations does not rely on pumped fresh replacement air, because it is always possible to utilise natural convection which draws in cooler air from the surface whilst discharging warm air from below. The air in the tunnels is always warmer than at the surface because over prolonged periods of time the tunnel walls are warmed by, and become heat sinks for, the heat generated by the moving trains. The London Underground system has been operating for more than a century, and during that time the tunnel walls have absorbed heat generated by the trains through: * traction drive and operation of the train's electric motors; * traction gearboxes; * after-coolers on air brake compressor sets; * air compressors; * friction brakes on the train's wheels; * passenger comfort heating; * carriage lighting; * passengers' body heat; and * electrical rectification of transformer equipment; and to a lesser extent by: * direct current power supply pick-up lines; * signalling systems; * the driver's cab cooling unit; and * safety access lighting.

The piston effect of a train passing along a single track tunnel has the effect of pushing a column of air along the tunnel in front of the moving train. The column of air is warmed by the tunnel walls, and when it reaches a station platform it rises and is replaced by cooler fresh air which is drawn down into the station by thermal convection. The better stations are designed to take maximum benefit from the thermal convection currents, thus maintaining a strong cycle of cool, fresh air down to platform level. As the train moves out from the platform its piston effect acts to drive the warm stale air in the tunnel on towards the next station up the line, whilst the air change at the station just vacated is continued by the piston effect of the next train down the line. But the above piston effect is enhanced when there is a minimal clearance between the train carriages and the tunnel wall. A typical train carriage might have a cross-sectional area of 5.8 m2, and a typical single track deep tunnel may have a free cross-sectional area of 10.5 m2, so that in practice the above minimal gap' train/tunnel clearance amounts to at most about 55% train occupancy in a deep tunnel between stations. If the efficiency were calculated as the cube of the train occupancy in the tunnel then a 55% occupancy would give a 17% efficiency (0.55).

It is an object of the invention to enhance significantly the efficiency of the piston effect of a train moving through a single track tunnel, and thereby to improve tunnel ventilation. The invention is based on the observation that an air curtain created across an orifice offers a resistance to air flow through that orifice.

Air curtains are commonly used across the entrances of open access' retail premises to enable shoppers to walk, through the air curtain, from a relatively cold (or warm) street into a relatively warm (or cool) shop. JP-11-030099A discloses the use of an air curtain to isolate a section of a twin-track railway tunnel during maintenance work, so that workers in that tunnel section are not affected by atmospheric conditions elsewhere along the tunnel. The air curtain is however created across the tunnel at a single fixed point or at two mutually spaced fixed points, with breathing air for the maintenance workers being ducted through the air curtain for their natural respirational needs. The air curtain of JP-1 1-030099A acts to restrict movement of air along the tunnel, and not to encourage it. It also shows an air curtain coverage over only the top half of the tunnel.

The Invention The invention provides an underground railway tunnel ventilation apparatus as defined in claim 1 herein. Preferred but optional features of the invention are as defined in the subclaims.

In use, the continuous air curtain extending from the carriage outline, being the outer periphery of the rolling stock, to the tunnel wall moves along the tunnel with the moving train and significantly increases the efficiency of the piston effect of the train as it pushes a column of air ahead of it as it moves along the tunnel. Preferably the apparatus is provided with electromechanical transducers on the train responsive to electromechanical devices on the tunnel wall. The transducers sense when the train is approaching a station and switch OFF the air curtain before the rolling stock exits the tunnel and enters the station. For example, transducers on or in the tunnel walls a fixed distance from the station platform ends can be effective to switch off the air curtain fans as the train approaches the platform and to re-start the air curtain as the train leaves the platform and enters the next tunnel section.

In addition to air fans which generate the air curtain, the ventilation apparatus preferably also comprises a fan system, carried by the same rolling stock, for creating a flow of ventilation air through the tunnel air space relative to the train and consequently through the carriages of the train. Such a flow of ventilation air is beneficial when the train is moving, but becomes significantly more important if the train stops in the tunnel. Such stoppages do happen occasionally when there is a breakdown or signal failure, or when another train on the line is forced to stop. For that reason underground train carriages include fan-operated ventilation systems, to help to maintain an acceptable temperature in the carriage even when the train is stationary. According to the invention such ventilation fans are preferably incorporated into the same item of rolling stock which carries the fans which generate the air curtain.

Advantageously the air drawn into the existing carriage ventilation system and the air creating the air curtain is filtered at the air inlet sides of the associated air fans.

Drawings The invention is illustrated by the drawings, of which: Figure 1 is a cross-section of a typical underground railway deep tunnel and station platform, with a train standing at the platform; Figure 2a is a longitudinal side elevation of the train; Figure 2b is a side elevation similar to that of Figure 2a, but with a ventilation apparatus according to the invention carried by rolling stock located between two carriages of the train; Figure 2c is an enlarged detail from Figure 2b, showing the apparatus a i rflows; Figure 2d is a simplified schematic section through one half of the apparatus of Figure 2c, illustrating its two complementary ducted airflow systems; Figure 3 is a half end elevation of the apparatus of Figures 2b to 2d (as if it was travelling out of the page towards the reader); Figure 4 shows the rear of the ventilation grilles and areas of air filtration of the apparatus of Figure 3; Figure 5 shows the rear of the air filter casings that lead to individual ductwork routes; Figure 6 shows the ductwork locations and transformations in the device of Figure 3; Figure 7 shows the ventilation ductwork as it passes through and between adjacent tangential air curtain ducts; Figure 8 shows the positions of reversible axial ventilation fans and chassis members; Figure 9 shows a plan of one half (as in Figure 3) of one end (as in Figure 2c) of the apparatus in horizontal section illustrating the layout of the lower level of fans, grilles and ductwork; Figure 10 shows one end (as in Figure 2c) of the apparatus in vertical section, illustrating the layout of the main air duct work systems, running wheels, air grilles, filters and carriage coupling; Figures ha and lib show a peripheral outer end, in longitudinal and in radial section respectively, of the perimeter air curtain duct and associated air flows; Figure 12 shows the anticipated air flows creating the air curtains for the front and rear air curtain ducts; Figure 13 shows at (a) a plan of the connection between two standard carriages indicating the lateral movement at their coupling when travelling round a tight bend, at (b') a plan of the same two carriages with a ventilation apparatus according to the invention on a bogey between the carriages, and at (b") an enlarged view of (b'); Figures 14 and 15 show cross-sections through a notional underground train station illustrating expected air movement patterns; Figures 16 and 17 are respectively a side elevation and a plan view from above of a train carriage in which the pressure fans and ducts of the ventilation car V of Figures 1 to 13 are provided in a short ventilation car section V' of the full length train carriage; Figure 18 is a schematic vertical section through the ventilation car section V' of Figure 16; Figure 19 is a schematic cross section through the left hand portion of the ventilation car Vt of Figure 17, showing the arrangement of ventilation grilles and filter boxes; Figure 20 is a schematic horizontal section through a preferred design of short ventilation car section V" to be incorporated into a full length train carriage just like the short ventilation car section V' of Figure 16; Figures 21 to 25 are schematic vertical sections in the planes P21 to P25 respectively of Figure 20; Figure 26 is a side elevation of the complete carriage incorporating the ventilation car section V"; and Figure 27 is a plan view of the carriage of Figure 26.

Figures 1 and 2a illustrate a conventional underground railway train at a station plafform. The train carriages 100 typically would have a cross-section of about 5.8 m2, and the tunnel through which the train runs (seen immediately around the train carriage in Figure 1) would typically have a cross-section of about 10.5 m2, so that as the train moves through the tunnel there is about 55% train occupancy in the tunnel.

Figures 2b and 2c illustrate a tunnel ventilation apparatus V according to the invention. The apparatus V is shown to be in this example a self-contained ventilation car on a short wheelbase rolling stock coupled between the middle two carriages. Of course the same ventilation car V could be mounted between the tractor car at the front or rear of the train and the adjacent carriage, or between any other pair of carriages. Figure 2c includes an arrow 66 indicating the current direction of movement of the train, although it will be understood that most underground trains are bidirectional, with a tractor unit and a driver's cab at each end. It is to this end that the ventilation car V is constructed with a central plane of symmetry and can be operated in either direction of motion of the train. Figure 2d, however, illustrates air flows for stationary and left-to-right motion only, as shown by arrow 66.

Figures 2c and 2d include a number of unreferenced arrows indicating air flows. Those arrows drawn with a composite shaft leading to the arrow-head 1o indicate air flow into the grilles and ducting described below, and those arrows drawn with a simple straight shaft indicate air flow from the grilles and ducting.

It should be understood, however, that there are two distinct air flows through the ventilation car V. On the one hand there are air flows to create the air curtains which seal the air space between the caariage and the tunnel and which enhance the piston effect of moving a column of air along the tunnel in front of the moving train. On the other hand there is a plurality of air flows which maintain a good supply of replacement breathing air for the passengers in the train carriages. Those individual air supplies will be referred to as air curtain air flows and ventilation air flows respectively (the latter referring to forward/upline tunnel and carriage ventilation).

It will be seen from Figure 2d that air curtain air drawn in through air grille/filter box assemblies 3 at the leading and trailing ends of the ventilation car V is compressed by centrifugal air fans 41a and 41b and supplied through a pair of peripheral air curtain pressure seal outlet ducts 1. Each peripheral air curtain pressure seal outlet duct I has an annular air equalising diffuser 49 (Figure 11) and directional vanes 2 dividing the air curtain air flow into components 72 and 73 angled inboard and outboard with respect to the neighbouring air curtain as shown in Figure 12.

Although only two each of the centrifugal air fans 41a and 41b are shown in Figure 2d, it will be understood that the fans 41a and 41b total eight in this example, four on each side of the longitudinal centre-tine as illustrated in Figure 7.

The direction of flow of the ventilation air at the train's terminus can be reversed on reversal of the direction of travel 66 of the train. This is achieved simply by reversal of the rotational direction of the impellers, to be described later, and by moving air filters from the ventilation air grille/filter box assemblies 4 at the rear end of the ventilation car V to front grilles 5 at the other end. The grilles 4 and 5 are symmetrical, but for the purpose of this description it is convenient to refer to the grilles 5 shown at the right hand side of Figure 2d as front grilles, which they are when the train is travelling from left to right as indicated by arrow 66.

Figure 3 shows a typical arrangement of the air curtain intake air, grilles 3 and ventilation supply air grilles 5 around a central corridor through the rolling stock. The corridor carries the reference number 8 in Figure 6. The corridor 8 has an airtight access door 6 at each end, each with a window 7, so that it effectively acts as an air-lock, allowing passengers to pass along the train whilst preventing a through-flow of air along that corridor while the train is in motion.

Figure 4 shows the rear of the air grillage boxes and ducting associated with the filter box assemblies 3 and 5 of Figure 3. Ventilation air grille/filter box assemblies 4 are associated with air filters 70 to 79, and the air curtain grille/filter box assemblies 3 are associated with a trio of air filters 80 and single filter 81. Figures 3 and 4 also show, indicatively, the carriage coupling 12 and Figure 4 shows the box member elements 9 of a chassis for the apparatus, which runs on four reduced diameter rolling stock wheels 11 as shown in Figure 6.

The ventilation air filters 70 to 79 lead to individual ventilation air ductwork routes 13 to 22 as shown in Figures 5 and 6, with shut-off dampers 82 to 91 at one end of the unit only. The ventilation air ductwork routes 13 to 22 lead on to ventilation air ductwork 23 to 32 (see in particular in Figure 7) which pass through and between air curtain radial ductwork 35 to 40 delivering air from the upper inlet grille 3 to an air curtain fan 41a, and through and between air curtain ductwork 42 to 47 delivering air from the inlet grilles 3 to a further air curtain fan 41b. Air curtain intake air ducts 33 and 34 have associated non-return dampers 92 and 93 for reverse air flow protection on fan motor failure at both ends of the unit. Fans 41a and 41b are centrifugal fans which rotate in opposite directions, enabling tangential duct connections. They deliver air to a common peripheral air curtain duct 48 which incorporates an air equalising diffuser 49. Everything so far described for the left hand side of the vertical centre-line of Figures 3 to 7 is of course repeated and mirrored for the right-hand side, except for the air curtain duct 48 and diffuser 49 which continue around the entire perimeter of the rolling stock. Everything so far described for the leading half of the apparatus is repeated and mirrored for the trailing half. Thus the air curtain duct 48 and air equalising diffuser 49 at the leading half of the apparatus together form the leading air outlet duct 1 of Figure 2d, and the air curtain duct 48 and air equalising diffuser 49 at the trailing half together form the trailing air outlet duct 1 of Figure 2d. The manner in which each air curtain duct 48 creates an efficient air curtain will be described later.

The fans which move the ventilation air through its ductwork 23 to 32 are reversible axial ventilation fans and are identified as 50 to 59 in Figure 8. One such fan, 52, has been shown in more detail to identify its connecting flange 60, reversible drive motor 61 and axial fan vanes 62. Figure 8 also indicates main structural supporting members 9.

A quadrant plan of the ventilation car V is shown in Figure 9, and represents a simplified lower half plan of the ventilation air fans 56 and 57, one of the air curtain centrifugal fans 41b, air curtain intake/ventilation supply air grilles 3 and 5 respectively and associated air curtain air filter 81, air curtain ductwork -10- 34, 42, 47 and ventilation air ductwork 19, 20, 29 and 30. Ventilation air as supplied by the ventilation air fans 56 and 57 is shown as a forward supply air flow 63, in the same direction as the train travel direction as indicated by arrow 66. Air curtain intake air is shown as an air flow 64. Also shown are typical structural steel axial fan supports 67 for the axial fans 56 and 57.

Figure 10 is a vertical half elevation of the ventilation car V with an outer casing removed to expose the relative positions of the main air ductwork, one of the running wheels (reduced to and shown as 450 mm diameter to decrease axle height and minimise the car overall length) the chassis elements 9 and the coupling 12. Also shown is the tunnel soffit 95 and rail track 96 Figures 11 a and 11 b together illustrate the detail of the outer periphery of the air curtain pressure seal duct 1. Air passes from the common peripheral air curtain duct 48 through the air equalising diffuser 49 and is deflected by the vanes of the air curtain discharge grille 2 into two air curtain flows, as indicated by the arrows in Figure lib. The resulting air curtain is explained with reference to Figure 12a which includes a reference numeral 95 indicating the tunnel floor, soffit or wall and arrow 66 indicating the train intended travel direction.

Figure 12b indicates the vectoral directions of the air curtain inboard air flows 72, and outboard air flows 73 (at present designed at 50m/s) when the train is stationary (shown as 73,) and when travelling at 4.0 rn/s (about 9 mph) (shown as 7311 with a long dashed line) and when travelling at 8.0 rn/s (about 18 mph) (shown as 73111 with a short dashed line). Above those speeds the air curtains become less effective.

Both the motion of the train and ventilation fans 50 to 59 separately create air pressure differentials, which cause the air pressure at location 68a to the rear of the ventilation car to be less than the air pressure at location 68b ahead of -11 -the ventilation car V. The air curtain air flows radially outwardly from each air curtain peripheral pressure seal duct 48 and is divided by the air grilles 2 into two flow paths 72 and 73. The air pressure at location 68c between the two air curtain pressure seal ducts 1 is higher than the air pressure at location 68b because the inboard air flows 72 have to force their way between the tunnel soffit floor or wall 95 and the outboard air flows73. The result is an efficient double air curtain seal between the air curtain pressure seal grilles 2 and the internal tunnel surfaces 95 as the air curtain extends all around the stationary or moving ventilation car V. The result is a greatly enhanced piston effect as the moving train pushes a column of warm air ahead of it, significantly more than the efficiency which the relative sizes of the train and tunnel alone would create. When the train is stationary the piston effect is lost, especially if two trains occupy the same tunnel section between the same two stations. This is when the conbined action of the two fan systems is of the greatest benefit to passengers and to the train driver.

Figure 12c at c' and c" indicates two trains occupying the same tunnel section between two stations, with a fire 105 or other life-threatening emergency occurring at the rear half of the lead train, or occurring between the trains, or occurring at the front half of the lag train. Without further control the air curtains would contain particulate dust-laden air or hot choking smoky gases 106, and the ventilation air would blow the same contaminated air towards the upline station. The necessary control is the shutting down of all ventilation fans, together with the rear air curtain fans of the lead train and the front air curtain fans of the lag train. All toxic fumes, smoky gases and particulate material resulting from the emergency situation are therefore contained within the local tunnel secion in which the emergency has occurred. This is shown in Figure 12c by the stretched' normal operation of the double air curtain air seal containing the airborne debris.

When a train follows a tight curve the mid-portion of each carriage 100 intermediate the front and rear bogeys pushes to one side of the track centre-line and the front and rear ends which overhang the bogeys push to the other side of the track centre-line as shown in Figure 1 3a. When the carriages are the same length and the bogeys are positioned the same distance from the front and rear of the carriages this creates no problem, as the connecting doors at the carriage ends remain in mutual alignment. The same is not true for a ventilation car V of short length, coupled between two full length carriages. It will be seen from Figure 13b' and from enlarged plan Figure 13b" that the natural tendency is for the connecting doors to move out of alignment if the ventilation car V remains centrally over the tracks as indicated by the solid line outline 101. According to one preferred aspect of the invention, therefore, the ventilation car V is capable of sliding laterally along its wheel axles to the position indicated by the broken line outline 102 in Figure 13b'. This maintains the connecting doors in better alignment for purposes of emergency egress. The mechanism for creating the lateral sliding movement along the axles is shown in Figure 6, which shows the wheel 11 in solid line at its central position on its axle and in broken line at the limiting positions to which it is pushed as the train negotiates sharp right-hand and left-hand curves respectively. The couplings 12 act to push the ventilation car V to one side or the other on bends, and strong springs (not shown) act to return it to its central position when the ventilation car reverts to straight line track running again.

Figures 14 and 15 illustrate how the act of pushing a column of air out of a tunnel into a station platform area contributes to an overall ventilation of the underground system. The air emitted from the tunnel is warmer, having been heated by the train components and the tunnel walls. It is also vitiated, having a depleted level of oxygen and an increased level of carbon dioxide and water vapour caused by the passengers' respiration in the trains and at the station.

The warmer lighter air rises as a rising convection current shown by the heavier split arrows 103 and is replaced by the denser cooler fresh air from the surface as shown by the lighter open arrows 104. This will apply throughout the year.

If the train is stationary between stations, its carriage temperature will soon rise because of the heating effect of the train components, passengers, lighting and tunnel walls. An onboard temperature sensor is preferably provided, which ensures that in such a situation the air ventilation fans 50 to 59 and the air curtain fans 41a and 41b are automatically activated when the carriage air exceeds certain predetermined thresholds. For practical reasons all fans (ventilation and air curtain) must be switched OFF when the train is at or passing a station platform. The air curtain is effective only when the train is stationary or moving through a tunnel, and has no practical use when the train is at a station platform. Moreover, the air blast from the air curtain supply grilles 2 would be directed against passengers standing on the station platforms. Therefore actuators are preferably provided in the tunnel walls a set distance from each station, and activate onboard transducers to turn OFF all fans when the train is approaching a station and to reactivate the system when the train leaves the station and re-enters a tunnel. Manual over-ride controls are of course also provided.

Another beneficial use for the tunnel ventilation apparatus as described is in conjunction with a tunnel cleaning train. Incorporation of the ventilation car V into a tunnel cleaning train has the effect of dislodging any clinging debris, dust and dirt from the tunnel walls and soffit and from electrical power and signal cables suspended therefrom, by the force of the air curtain. The dislodged contaminants may then more easily be picked up by the filtration system in the tunnel cleaning train, which power blasts air and vacuums the tunnel walls and floor but does not treat the soffit.

It will be understood, of course, that the ventilation car V does not have to be a short wheel base rolling stock coupled between two carriages or between a tractor unit and an adjacent carriage. The ventilation car rolling stock may be of carriage length, and all of the previously described air curtain air pressure fans and ducts together with all of the previously described ventilation air fans -14 -and ducts may be incorporated into one small portion of the carriage, isolated from the passenger-carrying areas. Such a combined carriage and ventilation car according to the invention would have to include ducting to permit the intake of air from around the front and rear of the ventilation car section as illustrated in Figures 16 and 17, in which the ventilation car section of a complete passenger carriage 100' is given the reference V'.

The ducting in the ventilation car section V' differs from that of the car V of Figures 1 to 13 principally in that both the ventilation air and the air curtain air is drawn in through different grilles depending on the direction of motion of the train. The intake air grille/filter box assemblies for air curtain air and for ventilation air are given the same references 3 and 4 respectively as in Figures 1 to 13 except that they carry primes "" to distinguish them from the respective grilles of Figures 1 to 13. For clarity in Figures 16 and 17 the lead lines from the reference numerals 3' and 4' end at the arrows indicating the intake air, but essentially those references indicate the air grille/filter box assemblies through which that intake air passes, just as in Figures ito 13. In addition, the grilles 4' are given the additional suffix A or P meaning "Active" or "Passive". When the carriage is travelling from left to right as viewed in Figures 16 and 17, as indicated by the arrow 68, the trailing air grille/filter box assemblies 4' for ventilation air are open and active, and are given the suffix A. The leading air grille/filter box assemblies 4' for ventilation air are closed and passive. The opening and closing of the air grilles can be achieved automatically by means of flap dampers such as the dampers 106 shown in Figures 16 and 18. Those dampers 106 when in line with their associated air ducts allow the ventilation air to travel through the relevant air filters indicated 107 and 108 in Figure 18, and when positioned across the duct direct the air towards supply air grilles 105. The filters can therefore be left in position when the train changes direction at a terminus, without the need to move them from one end to the other of the car V as in the embodiment of Figures 1 to 13. The air supply grilles 105 are also shown in Figures 16 and 17, carrying the suffix A or P as previously explained for the grilles 4'. -15-

A central corridor 8' is shown through the ventilation car section V', and is provided with two doors 6' which will be described in greater detail later.

The implementation of the device in carV as in Figures Ito 13 does not affect the passenger carrying capacity of the train, but lengthens the train by approximately 3.1 m. If car section V' of Figures 16 to 19 were to be the same length as car V of Figures 1 to 13 the overall train length would remain unaltered, but the maximum observed passenger capacity would fall by approximately 20 persons. By marginally increasing the length of the ventilation car section V' above that of ventilation car V, the maximum observed passenger capacity would fall by approximately a further 16 persons. The physical space thus released thus permits the inclusion of "either/or" flap dampers 106, and after the air curtain and ventilation air intake grilles 3' and 4' respectively, brush type air pre-filters 107, and short bag air filters 108 are accommodated allowing greater passenger comfort by increasing air quality, and less maintenance as the filter bags hold much greater mass of particulate matter, and negate the requirement for ventilation air filter relocation at the termini.

The ventilation car portion V' and shortened passenger compartments 100' are based on a standard trailer carriage 100. The integrity of the structural chassis 109 of the carriage would be maintained, and would include open mesh service and emergency egress flooring areas 110 to allow the through passage of ventilation air. The ventilation car V' has a greater ventilation air capacity than that of car V, which is achieved by the inclusion of an extra fanset, located under the corridor, as can be seen by comparig Figures 8 and 19.

A preferred design of ventilation car is illustrated in Figures 20 to 27. As with Figures 16 to 19, the ventilation car is a small section of a complete carriage, with a carriage-length rolling stock wheelbase. In Figures 20 to 27 the ventilation car section is given the reference V".

The ventilation air fans 50 to 59 of the previously described embodiments have been described as reversible axial vane fans. Such fans have good volume flow rate characteristics for their physical size, but have very limited air pressure capabilities, which is one reason for indicating two fans (twice the pressure) in series in the previously described embodiments. This is an important factor when considering the individual ductwork constraints required to pass the ventilation air ducts through and in between the radial ductwork of the air curtain system.

In order to solve this challenge, the ventilation car V" of Figures 20 to 27 uses centrifugal ventilation fans 113 without scroll casings. Such fans are known as plenum' or plug' fans. Although shown in the drawings as backward-curved centrifugal fans, they may alternatively be forward-curved. In place of the scroll casings of conventional centrifugal ventilation fans, the plenum fans 113 have, between adjacent fans, baffle plates 117 as shown in Figure 25.

The plenun fans 113 are mounted back to back on structural supporting steelwork 67", with air intakes facing each other. A section of straight circular ductwork 114 is connected between the intakes of each back-to-back pair of plenum fans 113, each of which has a single iris type shut-off damper in order to provide protection against back-flow in the event of a fan motor failure. As previously, suffixes A' and P' are applied to identify Active and Passive fans (and grilles), and only one of each back-to-back pair will be opwerating at any one time, depending on the direction of movement of the train. Thus for train movement in the direction of the arrow 68, the active fans 113A will be operative and the passive fans 11 3P Will be stationary. The active and passive roles will be reversed when the train direction changes. The air curtain system for unit V" is as previously described for V and V'. The ventilation system for unit V' is as previously described for V', but with the following variations. -17-

In addition to the two safety corridor doors 6" there is a pair of flap' air-sealing doors 111 across the centre of the corridor 8", such that a higher air pressure in the corridor space between an end door 6" and a flap door 111 will cause the nearer flap door 111 to close against its frame, to which it is air sealed.

The ventilation car V" utilises these central air seal doors 111 as a further air barrier thus allowing the corridor 8" to be used as two short ducts, which by-pass the air curtain radial ductwork systems. In contrast to the ventilation car V', in the car V" the ventilation unit casing around the air fans is air sealed.

The intake air grilles 4"A, brush filters 107, bag filters 108, and flap plate dampers 106 exist as described for unit V', but the ductwork terminates after the flap dampers 106 which have flared ends. The filtered ventilation air then passes either through the restricted gaps between the radial air curtain ductwork sections, or through air transfer grilles 112 located in the intake corridor wall, so that a proportion of the ventilation air takes the path of least resistance through the corridor (which thus acts as a duct).

Having either passed through duct spaces between the air curtain fans, or through the intake corridor section 8", the ventilation air re-enters the duct area around the corridoe 8" via a second air transfer grille 112. The ventilation air passes through the scroll of the stationary, or passive, plenum fan 113P, through the linking duct 114 with its iris damper, and enters the intake of the active plenum fan 11 3A. A similar air route is provided on the supply side, with ventilation air passing either through the second air curtain ductwork spaces or through the supply half of the corridor 8" via the transfer grilles 112. The higher air pressure maintains the air seal at the flap door 111. The ventilation air paths then again combine in the duct area surrounding the corridor 8" after the corridor air has passed through the final air transfer grilles 112. The air then passes around the flared ends of the ductwork for the ventialtion air intake, to be directed by flap dampers 106 to -18-leave the unit V" at 450 through grilles 105A, in order to ventilate the tunnel/carriage air space.

The corridor 8" is protected by fire shut-off dampers 115, installed at the rear of the air transfer grilles 112, to protect escaping passengers in case of fire in the fan and duct areas. It is not envisaged that the fans in the car V" will be operational whilst passengers are making emergency egress. Access into the corridor will therefore be made only after the operation of a safety button 116 (shown one at each end of the corridor 8") and/or after the operation of high temperature sensors initiates fan shut-down. -19-

Claims (9)

1. CLAIMS1. An underground railway tunnel ventilation apparatus comprising train rolling stock having the cross-sectional outline of a train carriage and, carried by that rolling stock, an air curtain generator which in normal mode of operaton draws in air from both ends of the rolling stock and ejects it as a continuous air curtain extending in use from the outer periphery of the rolling stock to the internal surfaces of a single track tunnel along which the rolling stock is designed to move.
2. 2. A ventilation apparatus according to claim 1, wherein the rolling stock is an integral part of a train carriage.
3. 3. A ventilation apparatus according to claim 1, wherein the rolling stock is a self-contained unit mounted on its own short wheelbase railway chassis and designed to be towed between two adjacent train carriages or between a tractor unit and a train carriage.
4. 4. A ventilation apparatus according to any preceding claim, wherein the air curtain generator comprises a plurality of air fans and associated ductwork.
5. 5. A ventilation apparatus according to claim 4, wherein the ductwork includes air filters for the air curtain airstream.
6. 6. A ventilation apparatus according to any preceding claim, wherein the air curtain generator draws in air from opposite ends of the rolling stock and ejects it as twin air curtains extending to the tunnel internal surface.
7. 7. A ventilation apparatus according to any preceding claim, further comprising means for generating a flow of ventilation air axially through the rolling stock.

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8. 8. A ventilation apparatus according to claim 7, wherein the means for generating the flow of ventilation air comprises a plurality of reversible axial flow fans and associated ductwork leading from a grille array at one end of the rolling stock to a grille array at the other end of the rolling stock.
9. 9. A ventilation apparatus according to claim 8, wherein the ductwork includes air filters for the ventilation air.