The invention relates to a leakage indication device for monitoring the pressure of a monitoring space. In particular, the invention is directed at the pressure monitoring of double-walled containers, pipes or the like. Single- walled containers with an internal covering can, however, also be correspondingly monitored using the leakage indication device. A leakage indication liquid may be partially located in the monitoring space. Various leakage indication devices are known from the prior art. These are used, in particular, when water-endangering liquids are stored or conveyed.

The leakage indication devices have to be constructed in a safety-directed manner. Each leakage detected has to be indicated optically and acousti- cally. Moreover, the leakage indication devices have to be checkable with respect to their functioning. The entire system also has to be checkable with respect to functioning.

Some of the known leakage indication devices have the drawback that to test the leakage indication device or to test the entire system, the lines running between the leakage indication device and the monitoring space have to be separated from the leakage indication device, which is labour- intensive. However, leakage indication devices, in which a separation of the lines between the leakage indication device and the monitoring space is unnecessary, are also known from the prior art. Three-way valves are generally used for this on the leakage indication devices. The drawback in these known leakage indication devices is, however, that there is a danger of the monitoring space not being monitored by the leakage indication device when a three-way valve is incorrectly set. This can have serious consequences.

The invention is therefore based on the object of providing a leakage indi- cation device, which allows extremely simple and rapid checking of the leakage indication device and the entire system. Furthermore, incorrect settings of the leakage indication device, in particular of the multi-way valve of the leakage indication device, are to be prevented for the operation of the leakage indication device.

The core of the invention is that at least one multi-way valve faulty position detecting means is provided, by means of which the at least one non- leakage indication operating position of the at least one multi-way valve of the leakage indication device is detectable. For example, the leakage indi- cation operating position of the multi-way valve can be indicated or the leakage indication operating position of the multi-way valve can be checked by means of the at least one multi-way valve faulty position detecting means. The multi-way valve is preferably manually adjustable. It is advantageous if the leakage indication device can only be put into operation when the multi-way valve is in its leakage indication operating position.

Two fluid connections are advantageously provided, the multi-way valves preferably being pivotable independently of one another.

The leakage indication device may also comprise a pump, which is then configured as an excess pressure and/or negative pressure pump. The pump is drivable by means of a motor, preferably an electric motor. A configura- tion without a pump is alternatively possible. The pressure element is preferably configured as a pressure switch, pressure sensor or the like. The pressure switch is then preferably configured as a mechanical pressure switch. It is advantageous if the pressure switch has a pressure-sensitive membrane, which acts on at least two micro switches. One micro switch switches the pump, while the other micro switch switches the alarm mechanism on and off depending on a set pressure value. The pressure switch may, however, also be an electronic pressure switch.

The leakage indication operating position is taken here to mean the position in which the pressure of the monitoring space can be properly monitored. The pump, if present, preferably has a flow connection here to the monitoring space, while the pressure element preferably has a pressure connection or a pressure-transmitting connection to the monitoring space. In the pressure connection, the pressure prevailing in the monitoring space can be detected by the pressure element.

The at least one non-leakage indication operating position is, on the other hand, taken to mean a position which is not the leakage indication operating position. A position of this type may be set, for example, in order to check the tightness of the leakage indication device. In this position, the pump, if present, does not have a flow connection to the monitoring space and/or the pressure connection between the pressure element and the moni- toring space is interrupted. A plurality of non-leakage indication operating positions are preferably possible.

The pump, if present, preferably has an electrical connection to the pressure element via a corresponding line. A wireless connection is alterna- tively possible. The leakage indication device preferably has a corresponding electromechanical or electronic controller for this.

Preferably, the leakage indication device has a leakage indication device housing and a movable closure flap, the closure flap preferably being movably mounted on the leakage indication device housing. The closure flap is preferably pivotably or foldably arranged on the leakage indication device housing. However, it may also be, for example, displaceably mounted on the leakage indication device housing. The closure flap may alternatively also be configured as a separate part. It can then preferably be connected or latched to the leakage indication device, in particular to the multi-way valve.

It is advantageous if at least the pump, if present, and the pressure element are accommodated in the leakage indication device housing. The at least one fluid connection is preferably located outside the leakage indication device housing. The at least one fluid connection may alternatively, however, also be located inside the leakage indication device housing. The controller may also be accommodated in the leakage indication device hous- ing.

Preferably, the closure flap, in its closed position, covers the at least one fluid connection, at least partially. The at least one fluid connection can be protected by such a configuration. It can thus be protected, for example, from soiling, mechanical effects or the like.

Preferably, the closure flap, in its closed position, can be secured to the leakage indication device housing, securing elements preferably being provided for this on the closure flap and on the leakage indication device hous- ing, which securing elements can only be mutually secured to one another in the closed position. The securing prevents, for example, a non-permitted actuation of the closure flap. This is particularly advantageous if the closure flap covers the at least one fluid connection, so the latter, in the closed position of the closure flap, is then protected from non-permitted actuation. A corresponding securing can be achieved, for example, by sealing.

It is advantageous if the closure flap in the at least one non-leakage indication operating position of the multi-way valve cannot be secured on the leakage indication device housing or on the multi-way valve. The user then discovers again that the multi-way valve is in a non-leakage indication operating position.

Preferably, the at least one multi-way valve faulty position detecting means indicates the at least one leakage indication non-operating position in that it is impossible to close the closure flap. The at least one leakage indication non-operating position is indicated in that the closure flap cannot be completely closed. The closure flap can only be completely closed when the multi-way valve is in its leakage indication operating position. The user of the leakage indication device thus recognises that a non-leakage indication operating position of the multi-way valve is present. In particular, the closure flap does not align with the leakage indication device housing when the multi-way valve is in its non-leakage indication operating position. The leakage indication device thus has no aligned external contour. A complete closure also includes an attachment of the separate closure flap on the multi-way valve.

Preferably, the multi-way valve has an actuating head with at least one element and the closure flap has at least one counter-element associated with the element, the element and the counter-element mechanically preventing a complete closure of the closure flap when the multi-way valve is in its at least one non-leakage indication operating position. The actuating head allows a simple, manual actuation or adjustment of the multi-way valve. It is advantageous if the actuating head is locked in the leakage indication operating position by the closure flap. The closure flap in its closed posi- tion preferably covers at least the actuating head of the multi-way valve.

Preferably, the element is formed by a closure-preventing stop and the counter-element has a closure-enabling recess, the closure -preventing stop engaging in the closure-enabling recess and the closure flap being com- pletely closable when the multi-way valve is in its leakage indication operating position. A complete closure of the closure flap is mechanically prevented when the multi-way valve is in its at least one non-leakage indication operating position. Preferably, the at least one multi-way valve faulty position detecting means indicates the at least one non-leakage indication operating position of the multi-way valve by at least one optical aid. This configuration allows a particularly simple and effective indication of the at least one non-leakage indication operating position of the multi-way valve. For example, the multi-way valve may be provided with a corresponding marking, which indicates the at least one non-leakage indication operating position. The marking is preferably printed on. It may alternatively be formed, for example, by an indentation, elevation or the like. Preferably, the at least one multi-way valve faulty position detecting means indicates the at least one non-leakage indication operating position of the multi-way valve by colour, preferably by red. This embodiment allows an indication without a reading of symbols, text or the like being necessary. It is advantageous if the at least one non-leakage indication operating posi- tion is indicated by the colour red, as this colour is in general understood to be a warning colour. The leakage indication operating position is, on the other hand, advantageously indicated by the colour green. A colour identification of this type is not absolutely necessary. Preferably, the at least one multi-way valve faulty position detecting means is configured as an electrical switching contact. The set position of the multi-way valve can easily be checked by the electrical switching contact. It is advantageous if a corresponding optical indication is then connected to the switching contact.

Preferably, the at least one multi-way valve faulty position detecting means is configured as a test sensor. A simple checking of the position of the multi-way valve is also possible owing to this configuration. A corresponding optical indication is helpful again here.

Preferably, it is possible to emit an alarm by means of the alarm mechanism in the leakage indication operating position. The emitting of an alarm may be an optical and/or an acoustic emitting of an alarm. A further detection of the at least one non-leakage indication operating position is possible, for example, by means of an electrical indication and/or a mechanically actuated element, such as a slide or the like.

A preferred embodiment of the invention will be described by way of ex- ample below with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic view of a leakage indication total system with a leakage indication device according to the invention and a monitoring space, shows a perspective partial view of the leakage indication device shown in Fig. 1 , in which the multi-way valves are in the leakage indication operating position, shows a simplified sectional view, which shows a multi-way valve in the leakage indication operating position, shows a perspective partial view of the leakage indication device shown in Fig. 1 , which shows the multi-way valves in a first non-leakage indication operating position, shows a simplified sectional view, which shows a multi-way valve in the first non-leakage indication operating position, shows a perspective partial view of the leakage indication device shown in Fig. 1 , which shows the multi-way valves in a second non-leakage indication operating position, shows a simplified sectional view, which shows a multi-way valve in the second non-leakage indication operating position, shows a perspective partial view of the leakage indication device shown in Fig. 1 , which shows the multi-way valves in a third non-leakage indication operating position, shows a simplified sectional view, which shows a multi-way valve in the third non-leakage indication operating position, Fig. 10 shows a plan view of the fluid connection of the leakage indication device shown in Fig. 1, the multi-way valve of which is in the leakage indication operating position, Fig. 1 1 shows a plan view of the fluid connection of the leakage indication device shown in Fig. 1, the multi-way valve of which is in the first non-leakage indication operating position,

Fig. 12 shows a plan view of the fluid connection of the leakage indi- cation device shown in Fig. 1, the multi-way valve of which is in the second non-leakage indication operating position, and

Fig. 13 shows a plan view of the fluid connection of the leakage indi- cation device shown in Fig. 1, the multi-way valve of which is in the third non-leakage indication operating position.

A leakage indication total system shown as a whole in Fig. 1 comprises a leakage indication device 1 , a double-walled storage container 2 with a substantially closed monitoring or intermediate space 3 and a connecting line system 4, which connects the leakage indication device 1 to a monitoring space 3. The gas pressure in the monitoring space 3 can be monitored by the leakage indication device 1. A leakage in the storage container 2 can thus be determined easily and rapidly.

The storage container 2 has an inner storage space 5, in which a liquid (not shown) to be stored can be kept. It has an internal wall 6, which spatially delimits the storage space 5 outwardly. The internal wall 6 is surrounded by an outer wall 7, which preferably has a substantially constant spacing from the internal wall 6. The monitoring space 3, in which a gas, such as air, is located, is present between the internal wall 6 and the external wall 7. The gas has a pressure. The storage container 2 may have any desired form. The leakage indication device 1 has a leakage indication device housing 8, which is preferably configured in the manner of a case. A closure flap 9, which can be pivoted between a closed position and an open position, is articulated to the leakage indication device housing 8. A pump 10, which can be driven by an electric motor (not shown), is preferably arranged in the leakage indication device housing 8. A dirt filter 1 1 is arranged in the leakage indication device housing 8 upstream of the pump 10. The dirt filter 1 1 is located in a suction line connection piece 12, which is connected on the suction side of the pump 10 and projects from the leakage indication device housing 8 at the bottom.

A first three-way valve 13 is arranged on the suction line connection piece 12 at the end outside the leakage indication device housing 8. According to Fig. 1, a suction line 14 is connected to the first three-way valve 13 upstream of the suction line connection piece 12, said suction line having a flow connection to the monitoring space 3. The suction line connection piece 12 is preferably configured as a one-piece component with the three-way valve 13.

Provided adjacent to the first three-way valve 13 in the suction line 14 is a first water separator 15, which is only necessary at deep points. A second water separator 16 is arranged in the suction line 14 adjacent to the storage container 2. A liquid barrier 17 is located in the suction line 14 between the first and second water separator 15, 16. The liquid barrier 17 protects the leakage indication device 1 from liquid and is used as the functional element to emit an alarm in the event of a liquid leakage. The liquid also guided in the suction line 14 may, for example, be accumulated condensate or ground water that has penetrated into the monitoring space 3 or, in the case of leakage, liquid from the storage container 2.

A pressure line connection piece 18, which projects from the leakage indication device housing 8 at the bottom next to the suction line connection piece 12, is connected to the pressure side of the pump 10.

An exhaust line 19 is connected, according to Fig. 1, to the pressure line connection piece 18, and in turn has a flow connection to a venting valve 20. The venting valve 20 is arranged on the storage container 2 and has a flow connection to the storage space 5 in order to allow venting thereof.

A pressure switch 21, which has a pressure-sensitive membrane 22 and a pressure element, is furthermore accommodated in the leakage indication device housing 8. Switching contacts 23 or 24 or switches can be switched by means of the membrane 22. The first switching contact 23 closes the electric connection between a current source (not shown) and the pump 10 or the motor associated with the pump 10. The second switching contact 24, on the other hand, closes the electric connection between the current source and an alarm mechanism (not shown). An alarm can be emitted by means of the alarm mechanism. The alarm mechanism may advantageously emit an optical and an acoustic alarm. A pressure sensor (not shown) may also be provided instead of a pressure switch 21.

A measuring line connection piece 25, which projects from the leakage indication device housing 8 at the bottom next to the pressure line connec- tion piece 18, is connected to the pressure switch 21. A second three-way valve 26 is arranged on the measuring line connection piece 25 at the end outside the leakage indication device housing 8. According to Fig. 1, a measuring line 27, which has a pressure connection to the monitoring space 3, is connected to the second three-way valve 26.

The connection line system 4 is formed by the suction line 14, the exhaust line 19 and the measuring line 27.

The three-way valves 13, 26 in each case have two outlets and one inlet.

The suction line 14 can be connected to the inlet 13a of the first three-way valve 13. The pump 10 has a flow connection to the first outlet 13b of the first three-way valve 13. The inlet 13a and the first outlet 13b oppose one another. The first three-way valve 13 also has a second outlet 13c.

The second three-way valve 26 is identically constructed. The measuring line 27 can be connected to the inlet 26a of the second three-way valve 26. The pressure switch 21 has a pressure connection to a first outlet 26b of the second three-way valve 26. The inlet 26a and the first outlet 26b oppose one another. Furthermore, the second three-way valve 26 has a second outlet 26c.

An outlet or two outlets of the three-way valves 13, 26 can be blocked in each case by valve bodies (not shown) of the three-way valves 13, 26. The two outlets may, however, also be unblocked. The valve bodies are arranged in valve housings 44 of the three-way valves 13, 26.

Each three-way valve 13, 26 has an actuating head 28, which is substantially plate-like. The actuating heads 28 are in each case pivotable about a pivot axis 29 in order to actuate the valve bodies in the valve housings. It is advantageous if the actuating heads 28 are oriented forward or backward and thus face or face away from a user.

The pivot axis 29 substantially extends perpendicular to the suction line connection piece 12 or to the measuring line connection piece 25.

Each actuating head 28 has an indication part 30 with an indication tip or indication nose 31 and a base part 32, which is, for example, configured in the shape of a part circle. In the region of the indication part 30, the actuat- ing head 28 linearly converges to form the indication tip 31. The position that has just been set of the three-way valve 13, 26 or the associated valve body can be seen from the indication tip 31. The actuating heads 28 are symmetrical with respect to a plane of symmetry, which goes through the indication tip 31.

Opposing the indication tip 31, a blocking web 33, which runs in an arcu- ately curved manner about the pivot axis 29, is provided on the base part 32. The blocking web 33 extends over an angular range of about 45° to 135°, more preferably from about 60° to 120°, most preferably from about 80° to 100°. The blocking web 33 advantageously has bevels 34 at the end. The blocking web 33 projects outwardly in the direction of the pivot axis 29. It preferably extends adjacent to the external edge of the base part 32. The blocking web 33 forms a first closure -preventing stop. The closure flap 9 is pivotably mounted by bearing arrangements (not shown) on the leakage indication device housing 8. The bearing arrangements predetermine a pivot axis 36 for the closure flap 9, about which pivot axis the closure flap 9 can be pivoted. The pivot axis 36 extends perpendicular to the pivot axis 29. It runs horizontally. To pivot the closure flap 9 between its open position and its closed position, an angular range has to be passed over, which preferably extends between 45° and 135°, more preferably between 60° und 120° and most preferably between 80° and 100°. The closure flap 9 is arranged on the leakage indication device housing 8 at the bottom. It may also be arranged at a different point on the leakage indication device housing 8. The fluid connections then also have to be placed accordingly at a different point.

At least one securing body pair 35 with securing bodies, which preferably have securing openings 35a and are advantageously configured in the man- ner of lugs, are provided on the closure flap 9 and on the leakage indication device housing 8. A securing body on the leakage indication device housing 8 is associated with each of the securing bodies provided on the closure flap 9. A plurality of securing body pairs 35 are preferably provided. The securing bodies on the closure flap 9 and the securing bodies on the leak- age indication device housing 8 are thus arranged in pairs and each have a continuous securing opening 35a. In the open position of the closure flap 9 or before the completely closed position thereof, the securing openings 35a of the securing bodies of the closure flap 9 are not congruent with the securing openings 35a of the securing bodies of the leakage indication device housing 8.

If the closure flap 9 is in its completely closed position, the securing openings 35a of the closure flap 9 are congruent with the securing openings 35a of the leakage indication device housing 8. The securing openings 35a of adjacent securing bodies are then aligned with one another. The closure flap 9 can thus be secured by the securing body pairs 35 on the leakage indication device housing 8, in that, for example, a seal is guided through the securing openings 35a of at least one securing body pair 35. The user thus recognises that the three-way valves 13, 26 are located in their leakage indication operating position. If at least one of the multi-way valves 13, 26 is located in a non-leakage indication operating position, the closure flap 9 cannot be completely closed. This results in the fact that the securing openings 35a on the closure flap 9 cannot be made congruent with the securing openings 35a on the leakage indication device housing 8. Consequently, no sealing can be carried out either. It is thus indicated to the user that at least one of the three- way valves 13, 26 is in its non-leakage indication operating position. Two stop bodies 37 are provided on the closure flap 9 on the inside. The stop bodies 37 are identical. A stop body 37 is associated with each actuating head 28 here.

The stop bodies 37 form second closure -preventing stops. The stop bodies 37 in each case have a closure -preventing stop face 38 and a closure- enabling recess 39 adjacent thereto. The stop bodies 37, in the region of their closure-enabling recess 39, have a reduced height compared to the closure-enabling stop face 38. The stop bodies 37 are non-movably attached to a base 40 or to a side wall 41 of the closure flap 9. They may be injected in one piece with the closure flap 9.

The functioning of the leakage indication total system will be described in more detail below. This is based on the leakage indication operating position of the two three-way valves 13, 26 with reference to Fig. 2, 3 and 10. In this position, the monitoring space 3 has a flow connection to the pump 10. The pressure switch 21 has a flow connection or pressure connection here to the monitoring space 3. The valve bodies of the three-way valves 13, 26 are in a corresponding position. The actuating heads 28 are likewise correspondingly oriented. This position of an actuating head 28 is shown in Fig. 10. In the leakage indication operating position, gas is sucked out of the monitoring space 3 via the suction line 4 into the pump 10. In the process, the fluid flows through the second water separator 16, the liquid barrier 17, the first water separator 15 and the first three-way valve 13. The gas then arrives in the suction line connection piece 12 and passes through the dirt filter 1 1, before it arrives in the pump 10. The gas then leaves the pump 10 again and flows via the pressure line connection piece 18 into the exhaust line 19. In the process, it flows through a third water separator 42, which is located in the exhaust line 19. The gas then flows to the venting valve 20.

The monitoring space 3 also has a pressure or flow connection via the measuring line 27 and the second three-way valve 26 with the pressure switch 21. A fourth water separator 43 is located in the measuring line 27.

The pressure switch 21 is connected via the measuring line 27 to the monitoring space 3. If the pressure in the monitoring space 3 rises, the first switching contact 23 is actuated to control the pump 10 by means of a plunger plate. The pump 10 is activated until the switch-off pressure in the monitoring space 3 has been reached again. The negative pressure decreases again when the lack of tightness is too great. A red lamp and also the acoustic alarm are triggered by means of the second switching contact 24 on reaching the alarm switch-on value. The pump 10 is constantly in operation here. The switching values to switch the pump 10 and the alarm mechanism on and off are preferably stored in an electrical or electronic circuit.

As can be seen from Fig. 3, in the leakage indication operating position, the indication tip 31 is directed in the direction of the lower side of the leakage indication device housing 8, in other words to the first outlet 13b or to the first outlet 26b. The blocking web 33 is thus arranged opposing the lower side of the leakage indication device housing.

The closure flap 9 can be completely closed in this position of the actuating head 28, in other words, it can completely conceal at least the actuating heads 28. It preferably then forms an extension of the front side or rear side of the leakage indication device housing 8. The blocking webs 33 namely engage, preferably positively, in the closure-enabling recesses 39. It is thus indicated to the user that the three-way valves 13, 26 are in their leakage indication operating position. This is also indicated by the described position of the actuating heads 28.

Referring to Fig. 4, 5 and 1 1, the three-way valves 13, 26 can be pivoted into a first non-leakage indication operating position. The actuating heads 28, compared with the leakage indication operating position according to Fig. 1 1 , have been pivoted by 90° in the clockwise direction, so the indication tips 31 are directed to the second outlets 13c, 26c of the three-way valves 13, 26, which form measuring connections. The blocking webs 33 are, on the other hand, oriented opposing with respect to the measuring connections 13c, 26c.

The pump 10 and the pressure switch 21 in each case have a flow or pressure connection to the monitoring space 3. Furthermore, the measuring connections 13c, 26c are open, so that a measuring apparatus can in each case be connected to them in order to measure the pressure ratios of the entire system.

The closure flap 9 cannot be completely closed here, as the blocking webs 33 rest on the closure -preventing stop faces 38 and do not engage in the closure-enabling recesses 39. The user thus recognises immediately that the three-way valves 13, 26 are not in their leakage indication operating position. Referring to Fig. 6, 7 and 12, the actuating heads 28 can be pivoted from the leakage indication operating position by 180° into a second non- leakage indication operating position.

The blocking webs 33 are now arranged adjacent to the lower side of the leakage indication device housing 8.

In this position, the pump 10 and the pressure switch 21 are separated from the monitoring space 3. The pump 10 has a flow connection to the measuring connection 13c of the first three-way valve 13, while the pressure switch 21 has a pressure connection to the measuring connection 26c of the second three-way valve 26. The tightness of the leakage indication device 1 can thus be checked.

The indication tips 31 are directed to the inlets 13a, 26a of the three-way valves 13, 26.

The blocking webs 33 rest on the closure -preventing stop faces 38 and do not engage in the closure-enabling recesses 39, so the closure flap 9 cannot be completely closed. The user thus learns again that the three-way valves 13, 26 are not in their leakage indication operating position.

Referring to Fig. 8, 9 and 13, the three-way valves 13, 26, proceeding from the leakage indication operating position, are furthermore pivotable into a third non-leakage indication operating position. The actuating heads 28 have to be pivoted for this purpose from the leakage indication operating position by 270° in the clockwise direction.

The blocking webs 33 face the measuring connections 13c. The pump 10 and the pressure switch 21 are separated from the monitoring space 3. For this purpose, the suction line 14 or the exhaust line 19 has a flow connection to the measuring connection 13c of the first three-way valve 13, while the measuring line 27 has a flow connection to the measuring connection 26c of the second three-way valve 26. The tightness of the monitoring space 3 can be checked here.

The blocking webs 33 rest on the closure -preventing stop faces 38, so the closure flaps 9 cannot be completely closed. The user is thus shown that the three-way valves 13, 26 are not in their leakage indication operating position.

The two three-way valves 13, 26 can, however, also be pivoted into positions which are not identical.

Thus, for example, the first three-way valve 13 may be located in its leak- age indication operating position, while the second three-way valve 26 may be located in its third non-leakage indication operating position. The blocking web 33 of the second three-way valve 26 thus rests on the closure- preventing stop face 38, so the closure flap 9 cannot be completely closed and it is indicated to the user that at least one of the three-way valves 13, 26 is not in its leakage indication operating position. A non-leakage indication operating position of the second three-way valve 26 can separate the pressure switch 21 with respect to the monitoring space 3, which can lead to a pressure change in the monitoring space 3 and in the measuring line 27 not being reliably detected here by the pressure switch 21. An emission of an alarm safeguarded in each case on reaching the alarm pressure value in the monitoring space 3 is therefore not ensured, which contravenes the specification principle of leakage indication devices to DIN EN 13160 Class I, "Safety-directed structure". Conversely, the second three-way valve 26 may be in its leakage indication operating position, while the first three-way valve 13 is in its second non- leakage indication operating position. The closure valve 9 cannot be completely closed here either. A pressure change in the monitoring space 3 is detected here by the pressure switch 21 and the pump 10 is activated.

However, the required switch-off pressure in the monitoring space 3 is not built up. The pump 10 thus runs in continuous operation. The pressure level in the monitoring space 3 can rapidly drop below the safety level.

An electrical switching contact (not shown) is preferably shown on the clo- sure flap 9. In the closed state of the closure flap 9 or in the incomplete state of the closure flap 9, a corresponding signal can be emitted. It is also possible to attach a switching contact at a suitable point in order to detect the correct operating position of the actuating head 28. It is expedient if test sensors are arranged on the three-way valves 13, 26 or if their positions are monitored by test sensors. Corresponding signals can then also be emitted here.

The described preferred embodiment of the invention is based on the nega- tive pressure principle. However, the invention can equally also be used in a pressure configuration. In the pressure configuration, the suction line 14 is configured as a pressure line. An exhaust line 19 is not then provided.