EP0478100B1 - Shut-off device for a gas duct - Google Patents

Abstract

The invention relates to a shut-off member, in particular in the form of a pivotable shut-off flap and for large gas ducts, which contains a plate-like shut-off element capable of being pressed against a housing sealing seat. To be able to guarantee reliable and secure shutting-off of large gas ducts, the shut-off member forms, together with an additional cover, a chamber which is closed off gastightly with respect to the two spaces of the gas duct and the pressure of which is monitored and differs from the pressures prevailing in the two gas-duct spaces. <IMAGE>

Description

The invention relates to a shut-off device for a gas line, in particular with a large cross section, according to the preamble of claim 1. Such a device is already known from document DE-A-3 813 663.

Shutoff devices of the type mentioned are known in practice in various embodiments. For the shut-off of gas and flue gas pipes, d. H. Pipelines and ducts, for example, plug-in disc valves based on the principle of a blind flange shut-off are known.

Since the capacities of existing and to be built plants are getting bigger, the associated gas pipes have to be designed with bigger and bigger dimensions. In the course of these increases in performance, shut-off devices were also approved by the responsible safety authorities, which in the gas flow direction had two butterfly valves arranged one behind the other, i.e. H. contain two shut-off levels one behind the other. The space formed between the butterfly valves must be acted upon with a barrier medium, the pressure above the form, d. H. the pressure of the first butterfly valve - in the gas flow direction.

In these gas lines to be shut off, it should also be borne in mind that they often contain corrosive gases, e.g. B. smoke gases of a coal-fired boiler system in the area of flue gas desulfurization systems. If the acid dew point of these gases is not reached due to operational reasons, highly concentrated ones form very quickly Acids, which are deposited in particular on the cold flap sides of a closed butterfly valve and cause corrosion damage there (e.g. so-called pitting). Damage of this type can be indicated in the previously described double flaps by a drop in the barrier medium pressure, so that appropriate measures can be taken to remedy this damage before the life of operating and maintenance personnel is acutely endangered. However, it is understandable that these shut-off devices with a plurality of butterfly valves or shut-off levels arranged one behind the other not only require a relatively large amount of space, but are also relatively expensive.

The invention is therefore based on the object to provide a shut-off device of the type required in the preamble of claim 1, which is characterized by its space-saving and relatively simple construction with reliable compliance with the necessary safety regulations.

This object is achieved according to the invention by training according to the characterizing part of claim 1.

Advantageous refinements and developments of the invention are the subject of the dependent claims.

In the embodiment according to the invention, the shut-off element, in particular the pivotable shut-off valve, contains an additional cover which is arranged at a sufficiently large distance from the plate-shaped shut-off body in such a way that this cover together with the shut-off body form a closed space (hollow body) and thus one opposite the two spaces of the Gas line sealed gas-tight Chamber forms. This ensures that a pressure prevails or is maintained within this closed chamber which deviates from the pressures which are present in the two spaces of the gas line (in front of and behind the butterfly valve). For this purpose, a pressure monitoring device is connected to the closed chamber.

If, when using this shut-off device according to the invention in a shut-off device for gas lines, the pressure inside the gas-tightly sealed chamber of the shut-off device (shut-off flap) changes compared to a set target pressure, then damage to the additional cover or the plate-shaped shut-off body is indicated. A gas transfer or exit to or from the gas spaces of the associated gas line is not possible due to the construction according to the invention. This monitoring for the full functionality of the shut-off device is guaranteed both when the shut-off position and when the shut-off passage (shut-off flap) is open.

This results in an important functional difference compared to a shut-off device for gas lines known from US 4,077,432, which has a so-called Venetian blind arrangement with respect to the shut-off devices. This is a shut-off device with several shut-off flaps lying close together in one level in the shut-off position, each of which can be rotated about its central axis into the open position in such a way that the flat sides of the shut-off flaps lie approximately parallel to the axis of the gas line, i.e. in the direction of flow and only represent a relatively small flow obstacle. It is typical of such louvre flaps that the seal between two immediately adjacent louvre flaps is caused by the direct mutual contact of the Louver dampers must be guaranteed and there are only fixed sealing seats in the area of the pipe casing or the housing of this shut-off device, against which the blind dampers can rest. This has the consequence that the usual introduction of sealing air into a circumferential sealing air duct formed on the inside of the gas line between the louvre flaps and the fixed sealing seat is possible without any problems since the sealing air duct is easily accessible from the outside. In contrast, the supply of sealing air in the area of the seal between the immediately adjacent louvre flaps is not so easy. In order to overcome this difficulty, US 4,077,432 provides for the introduction of sealing air through the axes of rotation of the individual louvre flaps designed as hollow shafts, for this to flow through the hollow louvre flaps and for the narrow end faces to exit through the passageways into the sealing air ducts, also in the area between the immediate ones a sealing air duct is formed in each case against mutually sealing louver flaps.

This known device only solves the problem of sealing air supply. There are no indications of the possibility of detecting leaks in the shutoff surface of the shutoff devices. The embodiment according to the invention differs from this in particular in that it sets a very specific pressure in the closed chamber of the shut-off element and monitors whether this pressure changes, ie whether the chamber has a leak, which is always an indication of damage to the walls of this chamber represents.

In the known embodiment, however, leakages regularly occur in the area of the sealing air ducts, since dust deposits must always be expected in the area of the seals or sealing surfaces. In this respect, even in the case of pressure monitoring of the sealing air supply (not provided in US 4,077,432), it would be difficult to give a reliable statement about damage to the shut-off bodies.
In particular, minor, ie incipient, damage can go undetected. However, this case remains safely controllable in the embodiment according to the invention, especially since the shut-off body can be monitored without interruption even when the shut-off body is open, that is to say when no sealing air is supplied.

The pressure monitoring device can advantageously be arranged on the outside of the gas line housing and in the line connection between the gas-tight chamber and an external pressure source for a shut-off medium, preferably a gaseous locking medium, the pressure monitoring device expediently via a flexible pressure medium line with the gas-tightly sealed chamber in the shut-off element connected is.

In principle, an underpressure or an overpressure of a predeterminable size can be introduced and maintained there in a suitably adapted manner via the monitoring device.

Since no barrier medium can escape from the gas-tight chamber when the shut-off element is undamaged, the use of only a relatively small pressure source, for example the use of a simple small bladder accumulator, is sufficient.

With this design according to the invention, even with relatively large dimensions of the associated gas lines, only one shut-off level (in comparison to the known shut-off devices with two shut-off levels or shut-off devices located one behind the other) needs to be provided for each shut-off device, which on the one hand takes up little space and on the other hand makes it relatively simple overall construction, especially with regard to the entire associated shut-off device, leads.

Fig.1

eine Perspektivansicht (mit teilweise herausgebrochenen Gehäuseteilen) eines ersten Ausführungsbeispieles einer Absperreinrichtung mit zwei nebeneinander angeordneten schwenkbaren Absperrklappen als Absperrorgane;

Fig.2

eine Perspektivansicht (mit teilweise herausgebrochenen Gehäuseteilen) eines zweiten Ausführungsbeispieles einer Absperreinrichtung in Form einer Gasweiche mit einer schwenkbaren Absperrklappe als Absperrorgan;

Fig.3 bis 7

perspektivische Teilansichten (in teilweiser Schnittdarstellung) durch den Bereich eines Klappenumfangsrandes und den Bereich des zugehörigen Dichtsitzes, jeweils für verschiedene Ausführungsvarianten.

The invention is explained in more detail below on the basis of a few exemplary embodiments illustrated in the drawings. In these drawings:

Fig. 1

a perspective view (with partially broken housing parts) of a first embodiment of a shut-off device with two pivotable butterfly valves arranged side by side as shut-off devices;

Fig. 2

a perspective view (with partially broken housing parts) of a second embodiment of a shut-off device in the form of a gas switch with a swiveling butterfly valve as a shut-off device;

Fig. 3 to 7

perspective partial views (in a partial sectional view) through the area of a flap peripheral edge and the area of the associated sealing seat, each for different design variants.

1 and 2, two main uses of the shut-off device according to the invention are explained, this shut-off device being designed in the form of the particularly preferred pivotable shut-off valve and used in gas lines of relatively large dimensions.

If one first considers the exemplary embodiment according to FIG. 1, two pivotable butterfly valves 1 and 2 — viewed in the gas flow direction — are arranged next to one another in the housing 3 of an associated shut-off device in a gas line, the first butterfly valve 1 and the second butterfly valve 2 being of the same type can be executed and driven and can thus shut off or release half of the cross section of the housing 3. The clear cross section of the housing 3 can correspond to an associated gas line, which is not illustrated in detail here. 1 shows the left, first butterfly valve 1 in its fully open position and the right, second butterfly valve in its completely closed position.

In their shut-off position, the butterfly valves 1, 2 lie sealingly against a housing 3 (on the inner walls) which is fixedly arranged within the housing 3 with a central web 35 and extends around the entire inner peripheral side of the housing 3 and with the entire peripheral edge region of each butterfly valve 1, 2 is in sealing engagement when the associated butterfly valve is closed. In this way, the spaces of the gas line located on different or opposite sides of the butterfly valves 1, 2 are separated from one another.

If one considers only the opened first butterfly valve 1 of the two similarly designed and actuatable butterfly valves, it can be seen that this or each butterfly valve is closed in the direction of arrows 6a by means of a valve actuating shaft 6 which can be rotated by a drive device 5, and - on the closed second butterfly valve 2 - can be opened according to arrows 6b. For this purpose, the flap actuation shaft 6 has a plurality of actuation arms 7 which are firmly connected to it and which engage on articulated connecting rods 11 on one side of the butterfly valve 2 or 1.

A suitable gear 8, which is part of the drive device 5, can be assigned to one end of each flap actuation shaft 6.

The embodiment according to FIG. 1 shows that a shut-off device for gas lines of relatively large dimensions can be designed with single-leaf as well as with multi-leaf swing flaps (in the latter case then side by side), each wing of such a swing flap being formed by a swiveling shut-off flap.

Another particularly advantageous application of the shut-off device according to the invention is the use in the form of a pivotable shut-off valve in a gas switch, as illustrated in FIG. In this case, however, only a single pivotable butterfly valve is used, which can be designed in the same way as the first butterfly valve according to Figure 1, so that it is also provided with the reference number 1.

In the case of FIG. 2, the butterfly valve 1 is used to forward an incoming gas stream symbolized by arrow 19 either via a first branch connection 17 in the direction of arrow 21 or - as set in FIG. 2 - via a second branch connection 18 in the direction of arrow 20 . The butterfly valve 1 can in turn be pressed tightly against the sealing seat 4 in the region of the second branch connection 18 or against the sealing seat 4 in the region of the first branch connection 17 by the flap actuating shaft 6 via actuating arms 7 and actuating link rods 11. The rotary movement of the flap actuation shaft 6 in one direction or the other can in turn be carried out by the drive device 5 with the gear 8, the ends of the actuation shaft 6 being supported in shaft bearings 9 with bearing housings 10.

If one now also considers, for example in FIG. 3, the cut partial perspective view (detail) through the peripheral edge region of a butterfly valve, e.g. B. 1, the cooperating sealing seat 4 and the sealing elements arranged between them (which will be explained in more detail later), then you can first of all recognize that each of the shut-off valves forming a shut-off valve 1, 2 has a closed cavity or a closed chamber 13. This chamber 13 results from the fact that each pivotable butterfly valve 1, 2 contains as a main part a plate-shaped shut-off body 14 and a preferably also plate-shaped additional cover 15, both of which are at a sufficiently large distance from one another and essentially parallel to one another to form a substantially flat, plate-shaped and sufficiently dimensionally stable component are firmly connected. The plate-shaped shut-off body 14 and the additional cover 15 together form the chamber 13, which is sealed gas-tight with respect to the spaces of the gas line (in front of and behind each shut-off flap) the pressures prevailing in the two spaces in front of and behind each butterfly valve 1, 2 of the gas line deviate. In order to maintain the above-mentioned pressure in the gas-tight chamber 13 in the manner required in each case, the chamber 13 is connected to a pressure monitoring device indicated at 16 in FIGS. 1 and 2.

The pressure monitoring device 16 is preferably arranged on the outside of the associated housing 3 (in FIG. 1) or 12 (in FIG. 2). It is also located in a line connection between the chamber 13 and a suitable, known (therefore not illustrated in more detail) pressure source for a barrier medium, the connection to the pressure source being indicated by a line section 22 that can be shut off, while the connection between the pressure monitoring device 16 and the gas-tight chamber 13 of each butterfly valve 1, 2 is essentially formed by a flexible pressure medium line 23 (see FIG. 1), so that the pivoting movement of the associated butterfly valve is not impaired by the connecting line to the pressure monitoring device 16.

It should be pointed out again in this context that it is important, with the line 22 blocked, that the pressure (negative pressure or positive pressure) within the gas-tight chamber 13 is maintained in each butterfly valve 1, 2 in a size which is significantly different from that in FIG pressures prevailing in the two rooms of the gas line, so that immediately in the event of leaks in the shut-off body 14 or in the cover 15 this can be indicated by a corresponding pressure change on the pressure monitoring device 16 in order to be able to immediately take measures to remedy the damage.

Assuming that when the butterfly valve is closed - in each case when viewed in the direction of flow of the gases - there is a pressure of P₁ in front of each butterfly valve 1 or 2, a pressure of P₃ behind each butterfly valve and a pressure P₂ within the gas-tight chamber 13 of the butterfly valve, then the following pressure conditions can occur during operation:
P₁ <P₂> P₃,
P₁> P₂ <P₃,
P₁>P₂> P₃,
P₁ <P₂ <P₃.

In addition, when the butterfly valve is open, a pressure P 1 and gas-tight within the gas line closed chamber 13 of the butterfly valve a pressure P₂ prevail or be maintained, these pressures P₁ and P₂ must always deviate from one another.

3 to 7, some training options for the flap peripheral edge on the one hand and for the housing sealing seat and also for sealing elements arranged therebetween are explained below. In all of FIGS. 3 to 7, only one peripheral edge section is shown on the example of the closed butterfly valve 1 and the associated longitudinal section of the housing sealing seat 4 on an enlarged scale; the overall arrangement can be easily imagined if one considers the application examples of the butterfly valve 1, 2 in FIGS. 1 and 2 in a corresponding manner.

Reference is first made again to the exemplary embodiment according to FIG. 3 already mentioned above. It can be seen here that the butterfly valve 1, which can be pivoted in the direction of the arrow 24 (corresponding to the arrows 6a and 6b in FIG. 1), has a peripheral wall 25 which closes the gas-tight chamber 13 towards the peripheral edge of the valve and which has the plate-shaped shut-off body 14 and the likewise plate-shaped cover 15 connects to each other in the area of their peripheral edges, d. H. this peripheral wall 25 can be welded gas-tight to the peripheral edges of the shut-off body 14 and the cover 15.

In this exemplary embodiment (FIG. 3), the peripheral wall 25 - viewed in cross section - merely provides the inner leg of a cross-sectionally U-shaped circumferential groove, the outer leg of which forms an outer circumferential wall 27. As can be seen in FIG. 3, the circumferential trough 26 with its walls 25 and 27 protrudes from the plane of the additional cover 15 against the sealing seat 4, the side of the circumferential trough 26 pointing towards the sealing seat 4 being open. On the free edges of the inner peripheral wall 25 and the outer wall 27 facing the sealing seat 4, in this exemplary embodiment, rubber-elastic sealing strips are attached by means of clamping strips 29, which ensure sufficient sealing of the peripheral groove 26 forming the outer peripheral edge of the butterfly valve 1 with respect to the housing sealing seat 4 wear. The walls of this circumferential channel 26 simultaneously delimit a barrier medium cavity 30 which is open towards the housing sealing seat 4 and which will be discussed again below.

As can also be seen in FIG. 3, the housing sealing seat 4 contains a hollow body 31 or the sealing seat 4 is essentially formed by this hollow body 31, which is arranged on the corresponding inner wall region of the housing (arrangement roughly corresponding to FIGS. 1 and 2 ). The interior of this hollow body 31 can be acted upon by at least one pipe connection piece 32 with a pressurized barrier medium, which can be brought in from a separate pressure source for the barrier medium or from the pressure source connected to the gas-tight chamber 13. The side 31a of the hollow body 31 which is opposite the peripheral wall region of the butterfly valve 1, in this case the peripheral groove 26, and which can also be referred to as a sealing seat surface, has either - over the length of the hollow body - as shown in Figure 3 - a number of appropriately distributed through openings 33 or one or more sufficiently large slots, which - as can be seen in Figure 3 - are each designed and arranged so that they are from the open side of the circumferential groove 26th delimiting sealing strips 28 are included, so that when the shut-off valve 1 lies sealingly against the sealing seat 4 in its shut-off position, an open connection between the interior of the hollow body 31 and the barrier medium subspace 30 of the circumferential groove 26 is established via the through openings 33. If, therefore, in the shut-off position of the butterfly valve 1, the interior of the hollow body 31 is acted upon with a suitable barrier medium (preferably a gaseous barrier medium), then the flap peripheral edge region is also subjected to this barrier medium through the partial space 30 of the peripheral groove 26. In this way, an extremely reliable seal between the peripheral edge of the butterfly valve 1 and the housing sealing seat 4 is guaranteed.

4 shows an embodiment variant of the exemplary embodiment just explained with reference to FIG. Since this embodiment variant differs in the main only in the type of sealing elements and the circumferential groove adapted therein compared to FIG. 3, the same reference numerals can be chosen for the similar components, which means that these parts need not be explained again.

In the case of FIG. 4, the U-shaped circumferential groove 26 ′, which essentially forms the outer peripheral edge region of the butterfly valve 1, is only slightly wider than the circumferential groove 26 in FIG. 3. To the against the housing sealing seat 4 facing outer edges of the inner circumferential wall 25 and outer circumferential wall 27 of the circumferential groove 26 'are provided in this embodiment as circumferential sealing elements two spring steel strips 34 bent approximately in cross section, which are fastened and clamped on the inner sides of the circumferential walls 25 and 27 In the shut-off position of the butterfly valve 1, place it tightly against the housing sealing seat 4 under elastic deformation.

FIG. 5 illustrates a further embodiment variant of the embodiment described with reference to FIG. 3, so that here again all parts of the same type can be provided with the same reference symbols. The main difference of this embodiment variant compared to Fig. 3 and Fig. 4 can be seen in the fact that the seals 28 'on the barrier medium subspace 30 are designed in the form of keder seals.

3, 4 and 5 in the exemplary embodiments according to the previously explained FIGS. 3, 4 and 5, a circumferential channel essentially forming the flap peripheral edge region with the barrier medium subspace 30 delimited by it - viewed in cross section - is oriented approximately at right angles to the gas-tight chamber 13 of the butterfly valve 1 and is open , there is also the possibility, in the manner illustrated in FIG. 6, of forming a circumferential channel 36 with a U-shaped cross section in an outward (toward the outer peripheral edge) extension of the gas-tight chamber 13 provided between the shut-off body 14 and the cover 15. If one considers the U cross-section of this circumferential groove 36, then the transverse web of this U forms the circumferential wall 37 which closes the chamber 13 to the flap circumferential edge, while in a roughly straight extension of the cover 15 to the outside a circumferential wall part 38 as a longer U-leg and approximately in a straight line Extension of the shut-off body 14, a peripheral wall part 39 are formed as a shorter U-leg. Each of these two peripheral wall parts 38, 39 carries on its free edge pointing towards the housing sealing seat a flat, circumferential, rubber-elastic sealing lip 40, which is assigned a cover strip 41 on one side (in each case on the upper side in FIG. 6).

In this exemplary embodiment according to FIG. 6, the housing sealing seat 4 also contains a hollow body 42, which is connected to an external barrier medium pressure source via a pipe connection piece 43. This hollow body 42 is delimited - apart from the outer housing wall - by a narrow circumferential wall 42a and a broad circumferential wall 42b, the clear distance between these two circumferential walls 42a, 42b being the clear distance between corresponds to the peripheral wall parts 38 and 39 of the peripheral groove 36. In the shut-off position of the butterfly valve 1 shown in FIG. 6, the inward-facing free edge of the narrow circumferential wall 42a is also opposite the outward-pointing free edge of the sealing lip 40 on the longer circumferential wall part 38, while the inward-pointing free edge of the wider circumferential wall 42b of the hollow body 42 of the outwardly facing free edge of the sealing lip 40 bears against the shorter peripheral wall part 39 of the butterfly valve 1; The cover strips 41 each abut a side surface of the associated peripheral wall 42a or 42b of the hollow body 42. In this way, the butterfly valve 1 can only be opened in the direction of arrow 44 and pivoted into the shut-off position (FIG. 6) in the opposite direction to arrow 44.

In this case too (FIG. 6), a barrier medium subspace 30 is again formed within the circumferential groove 36, which is open to the outside, that is to say in the direction of the hollow body 42, and is in open communication with the inside of this hollow body 42 when the Butterfly valve 1 is in its shut-off position.

Finally, an exemplary embodiment will be explained with reference to FIG. 7, in which the sealing elements between the sealing seat hollow body and the flap peripheral region are not provided on the latter, but on the sealing seat hollow body.

In FIG. 7 it is again assumed that the shut-off device is the shut-off valve 1, the gas-tight chamber 13 of which is essentially made up of the plate-shaped shut-off body 14 and the plate-shaped one additional cover 15 is formed. In this case, however, the gas-tight chamber 13 towards the flap peripheral edge is formed by the web 45 of a circumferential steel profile 46, which is illustrated in FIG. 7 as a double-T profile, but also by another suitable steel profile, such as, for. B. U-profile can be formed.

Also in the example according to FIG. 7, the housing sealing seat 4 contains a hollow body 47, which in turn can be connected by a pipe connection piece 43 to an external barrier medium pressure source in order to be able to introduce barrier medium under pressure into the interior of the hollow body 47 in the manner explained. According to this example, the hollow body 47 can have an approximately U-shaped cross section and run in a channel shape over the inner peripheral region of the associated housing, its open channel side pointing towards the side facing it in the peripheral edge region of the butterfly valve 1, in particular its shutoff body 14. The hollow body 47 has two walls 47a and 47b directed against the butterfly valve 1, each of which carries a suitable circumferential sealing element 48 on its free edges, which comes into sealing engagement with the opposite side of the butterfly valve 1 when the butterfly valve 1 is in its shut-off position located. In this example in FIG. 7, it is again assumed that the two circumferential sealing elements 48 are formed by spring steel strips which are bent and clamped approximately in a U-shaped cross section, approximately the same as in the example in FIG.

Claims (12)

1. Shut-off device for a gas conduit, in particular of a large cross section, with a gas conduit housing which can be fitted into the gas conduit and with at least one shut-off member, in particular a pivotable shut-off flap (1, 2), the shut-off member comprising a plate-shaped shut-off body (14), which bears in a sealing manner against a sealing seat (4), which is firmly connected to the gas conduit housing, in the shut-off position and thus separates from one another the spaces of the gas conduit which are on different sides of the shut-off member, and the sealing seat (4) extending around the entire periphery of the plate-shaped shut-off body (14) in the edge area of the latter, characterised in that the shut-off member (1, 2) comprises an additional cover (15) which forms with the shut-off body (14) a chamber (13) which is closed off in a gastight manner from the two spaces of the gas conduit, the pressure (P₂) of which differs from the pressures (P₁ and P₃) in the two spaces of the gas conduit and which is connected to a pressure monitoring device (16).
2. Shut-off device according to claim 1, characterised in that the pressure monitoring device (16) is arranged on the outside of the gas conduit housing (3, 12) and in the connecting line (22, 23), which can be shut off, between the gastight chamber (13) and an external pressure source for a barrier medium, preferably a gaseous barrier medium.
3. Shut-off device according to claim 2, characterised in that the pressure monitoring device (16) is connected to the gastight chamber (13) in the shut-off member (1, 2) via a flexible pressure medium line (23).
4. Shut-off device according to claim 1, characterised in that the pivotable shut-off flap (1) forming the shut-off member comprises a peripheral wall (25, 37, 45) which closes off the gastight chamber (13) from the peripheral edge of the flap and connects together the plate-shaped shut-off body (14) and the cover (15), which is also plate-shaped, in the area of their peripheral edges.
5. Shut-off device according to claim 4, in which the peripheral edge area of the shut-off flap (1, 2) can be pressed in a sealing manner against the sealing seat (4), characterised in that this housing sealing seat (4) comprises a hollow body (31, 42, 47), which can be acted upon by a barrier medium under pressure and whose side which is opposite the shut-off flap (1) can be closed by a side of the peripheral area (26, 26′, 36) of the flap, with circulating sealing elements (28, 28′, 34, 40, 48) being arranged in between.
6. Shut-off device according to claim 5, characterised in that the peripheral wall (45) of the shut-off flap (1) is formed by a circulating steel section (46), in particular a channel section or an I-section, the sealing seat hollow body (47) being open on its side which is opposite the peripheral edge area of the shut-off flap (1) and bearing two sealing elements (48), which extend over the length of the sealing seat (4), contact a side face (14) of the flap so as to form a seal and define this side of the hollow body.
7. Shut-off device according to claim 5, characterised in that the shut-off flap (1) bears two sealing elements (28, 28′, 34, 40), which circulate at a spacing from one another, in its peripheral edge area (26, 26′, 36), which elements define with the peripheral wall (25, 25′, 37) of the flap a barrier medium subspace (30), which is open towards the housing sealing seat (4) and can be connected to the interior of the sealing seat hollow body (31, 42), and are pressed in a sealing manner against the opposite, at least partly open side of this hollow body when the shut-off flap is in the closed state.
8. Shut-off device according to claim 5, characterised in that the peripheral edge area is essentially formed by a peripheral channel of an approximately U-shaped cross section, one wall of which forms the peripheral wall closing off the chamber (13) from the peripheral edge of the flap and which defines the barrier medium subspace (30).
9. Shut-off device according to one of claims 5 to 8, characterised in that the circulating sealing elements provided between one side of the hollow body (31) and the peripheral wall area of the shut-off flap (1) are formed by elastomeric sealing strips (28, 28′).
10. Shut-off device according to one of claims 5 to 8, characterised in that the circulating sealing elements provided between one side of the hollow body (31, 47) and the peripheral wall area of the shut-off flap (1) comprise bent, clamped spring steel strips (34, 48) of an approximately U-shaped cross section.
11. Shut-off device according to one of claims 5 to 8, characterised in that the circulating sealing elements provided between one side of the hollow body (31) and the peripheral wall area of the shut-off flap (1) are formed by elastomeric sealing lips (40) with associated cover strips (41).
12. Shut-off device according to one of claims 1 to 11, characterised in that at least two shut-off flaps (1, 2) are provided which are arranged next to one in a common plane in the shut-off position, the sealing seats for the facing edges of the shut-off flaps (1, 2) in each case being arranged on a central crosspiece (35), which extends transversely through the gas conduit, of the gas conduit housing.

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