Shutdown device for a recirculation loop in a fuel cell stack - Patents.com

Abstract

The present invention relates to a shutoff device for a recirculation loop (40) in a fuel cell stack, which comprises a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54). In order to eliminate the need for several valves, a recirculation loop shutoff valve (20) is provided which is switched by an upstream hydrogen switching valve (22) and which integrates a purge valve (44) which is also designed as a pressure relief valve (44).

Description

[Technical field]

[0001] The present invention relates to an interruption device for a recirculation loop in a fuel cell stack, comprising a hydrogen inlet, a recirculation gas inlet and a purge line. [Background technology]

[0002] Fuel cells convert the chemical energy of a fuel into electricity through reaction with oxygen (usually from the air). The most commonly used fuel is hydrogen. Therefore, in the following, "hydrogen" will always be used to refer to the fuel, but this explicitly includes other gaseous fuels such as butane, propane, methane, methanol, or other hydrocarbons.

[0003] Low-temperature fuel cells are known that have an ion-conducting polymer electrolyte that separates the anode from the cathode. Hydrogen is supplied to the anode compartment and oxygen to the cathode compartment. The hydrogen ions move through the electrolyte while the electrons move through an electrical circuit and a consumer outside the cell. Such PEM fuel cells are also called polymer electrolyte fuel cells (PEFC), proton exchange membrane fuel cells (PEMFC) or solid polymer fuel cells (SPFC). Fuel cells normally only generate a voltage of about 1 V, so to achieve a higher overall voltage, several cells are usually connected to form a so-called stack.

[0004] During operation, hydrogen fuel cells are supplied with more than the stoichiometric amount of hydrogen, which means that they do not consume all of the hydrogen in the anode compartment, otherwise liquid water and inert gases would accumulate. In order not to waste the excess hydrogen, it is recirculated, i.e. fed to a recirculation system. For this purpose, there is the possibility of actively circulating the hydrogen using mechanical pumps or blowers. This is known, for example, from WO 2012 / 104191 (or the corresponding US 2013 / 0344406 A1).

[0005] The device comprises a shutoff device for the recirculation loop, a hydrogen inlet, a recirculation gas inlet and a purge or flushing line. This device forms the preamble of claim 1.

[0006] It is also possible to circulate hydrogen passively by providing a jet pump with a nozzle for fresh hydrogen, which delivers the recirculated hydrogen with a higher fresh hydrogen pressure. Such a hydrogen supply with passive recirculation is known from US 2020 / 0144642 A1.

[0007] In some operating situations, it is necessary or desirable to prevent return of the recirculation loop. This is accomplished via a shutoff valve for the recirculation loop.

[0008] Furthermore, over the course of operation, the recirculated gas accumulates nitrogen and other undesirable gases, which must be vented from time to time depending on the operating strategy. This is done via a purge or exhaust valve. When purging or exhausting the undesirable gases, it is advantageous to prevent recirculation.

[0009] Additionally, a pressure relief valve is required for safe operation, which will automatically open at a certain pressure, thus protecting all components from damage or, in the most extreme cases, from exploding.

[0010] Therefore, three valves are required to allow safe operation, an expense that cannot be considered negligible. Summary of the Invention [Problem to be solved by the invention]

[0011] It is therefore an object of the present invention to reduce the cost of valves for fuel cells having recirculation loops. [Means for solving the problem]

[0012] According to the invention, this object is achieved by a blocking device having the features of claim 1. Preferred embodiments of the invention are set out in the dependent claims and in the following description, which may each represent an aspect of the invention individually or in combination.

[0013] According to the present invention, a shut-off device for a recirculation loop in a fuel cell stack is provided with a hydrogen inlet, a recirculation gas inlet and a purge line, is provided with a recirculation loop shut-off valve that is switched by an upstream hydrogen switching valve, and has an integrated purge valve that is also designed as a pressure relief valve.

[0014] According to the present invention, therefore, three valve functions are combined in a single valve or component: a shutoff valve for the recirculation loop, a purge valve and a pressure relief valve. This can save both the cost and the effort associated with several valves, and can greatly simplify the control effort, since only one actuator is needed for all three functions. The shutoff valve according to the present invention is suitable for fuel cells with both active and passive recirculation. The inventors have also recognized that there is a special relationship between purging and shutting off the recirculation.

[0015] In a preferred embodiment, the upstream hydrogen switching valve is essentially a conventional control valve that opens or closes an orifice, whereas the recirculation loop shutoff valve is a sliding valve whose valve piston can partially or completely close a somewhat larger line during its movement, and at the same time mechanically actuate the purge valve. A single actuator is then sufficient to shut off and open the recirculation and purge lines. The sliding piston preferably moves transversely to the lines to be opened and closed.

[0016] The purge valve is preferably actuated, i.e. opened, via a mechanical connection, preferably a tappet. This tappet is preferably integrated directly into the valve slide of the recirculation loop shutoff valve. If the recirculation loop shutoff valve is closed, the mechanical connection automatically opens the purge valve by direct coupling. One design variant of the tappet is that the purge valve opens when the recirculation loop shutoff valve is completely closed. The opening time varies due to different tappet lengths. A fixed tappet length means that there is a fixed opening time. As shown in the following figure, the purge can start when the recirculation loop is 100% closed. Other design variants or tappet lengths can also be used, for example, the purge can start when the recirculation loop is 50% closed or 10% closed.

[0017] The hydrogen switching valve and the purge valve are preferably seat valves and therefore completely sealed. The purge valve also preferably performs the pressure relief valve function and is therefore recommended to be designed as a spring-loaded check ball valve, the spring being adjusted to the maximum permissible operating pressure.

[0018] According to the invention, the recirculation loop shutoff valve is controlled by the high hydrogen pressure in the reservoir (currently up to 900 bar), and the hydrogen supply pressure actuates the valve slide of the actual recirculation loop shutoff valve. This can be the maximum reservoir pressure, but also another lower pressure specified by the operator if desired. In some embodiments, a medium hydrogen pressure range is used, for example up to 25 bar. The shutoff valve, which often has a significantly larger diameter, especially in the case of passive recirculation, is not moved by its own electric actuator, i.e. by an auxiliary force, but is, so to speak, triggered and opened by another force, according to the invention. Here, we use energy that is already available as pressure energy in the stored fresh hydrogen or in the medium pressure range, and that is available on site. After all, the relatively high pressure (force per area) of the hydrogen reservoir exerts a relatively high force when it hits the piston (or its area), which makes the large piston move safely and reliably. In addition, the actual recirculation loop shutoff valve also moves the purge valve, which also does not need its own control.

[0019] In this case, to use the hydrogen pressure, a hydrogen selector valve is connected upstream of the recirculation loop isolation valve and the purge valve. The hydrogen selector valve can then be relatively small and moved by a small actuator. This upstream valve then switches the higher hydrogen pressure to the recirculation loop isolation valve. Because the hydrogen supply pressure is significantly higher than the pressure in the stack's recirculation loop, the actual valve slide of the recirculation loop isolation valve moves to the "recirculation loop closed" valve position due to the pressure difference. The recirculation loop isolation valve then completely closes the recirculation loop, but at the same time supplies fresh hydrogen to the stack, so that operation can still continue.

[0020] The strokes and cross sections of the three valves can be freely selected over a wide range. It is preferable that the valve stroke of the recirculation loop shutoff valve is independent of the valve stroke or armature stroke of the hydrogen switching valve and the purge valve. This means that, so to speak, it only provides the driving force for the movement of the recirculation loop shutoff valve, so that a small valve stroke is sufficient to allow the high hydrogen reservoir pressure to act on the recirculation loop shutoff valve, which can then be moved with a much larger stroke.

[0021] The switched cross section of the recirculation loop shutoff valve is also independent of the cross section of the hydrogen switching valve. Even a small diameter switching valve may allow high hydrogen pressure to reach and move a large diameter recirculation loop shutoff valve. The cross section or diameter of the recirculation loop shutoff valve can be freely selected and depends, for example, on the prevailing pressure conditions between the hydrogen supply pressure and the recirculation loop pressure in / on the stack.

[0022] The hydrogen selector valve may be controlled in a known manner, for example pneumatically, hydraulically or mechanically, preferably the control may be electrical or electromagnetic, for example via a solenoid valve having an armature within a plunger coil.

[0023] The piston of the valve moved by the actuator can be actively pushed in both one and the other direction, for example moved in one direction by the flow of current and in the other direction by the opposite current. In a preferred embodiment, the hydrogen switching valve and / or the recirculation loop shutoff valve and / or the purge valve each have a restoring mechanism, preferably each with an integrated restoring spring. This restoring component then causes the movement in the opposite direction. The restoring element or spring preferably moves one, two or all three valves to a so-called fail-safe position. This means, for example, that the restoring spring of the hydrogen switching valve pushes the hydrogen switching valve to a closed position, so that in the event of a power failure or another fault in the control system, the hydrogen switching valve is closed, leaving the downstream recirculation loop shutoff valve open, thereby keeping the normal recirculation loop open. This also means, for example, that the restoring spring of the recirculation loop shutoff valve pushes the recirculation loop shutoff valve to the open position so that in the event of a power outage or another fault in the control system, the recirculation loop shutoff valve stays open, i.e. the normal recirculation loop remains open. This is accomplished via two springs. The fail-safe positions of the purge valve and pressure relief valve are closed to maintain normal operation under slight overpressure.

[0024] In an embodiment with two valves connected in series, one valve, here the hydrogen switching valve, is controlled and the other valve, here the recirculation loop shutoff valve, is pushed into a closed position by the high pressure gas flow, but it is expedient to provide a mechanism that allows the second valve to slide back to its initial position after a certain period of time. This can be a small hole that releases pressure after the first valve closes, allowing the second valve, the recirculation loop shutoff valve, to return to its normal position after a certain period of time. In a preferred embodiment, the valve slide of the recirculation loop shutoff valve has a certain amount of leakage, i.e. it does not seal completely against the housing, so that the introduced gas escapes and the valve slide returns automatically, for example via its restoring spring. Without this leakage, pressure equalization would not take place. This can be done by increasing the radial guide play and / or by holes and / or by relief grooves.

[0025] If the fuel cell is intended to drive a vehicle, the hydrogen must be transported with the vehicle and stored in some type of tank. For this purpose, it is stored either in liquid form or under pressure. Since extremely low temperatures (up to a few Kelvin) are required for liquid storage, storage under pressure (up to about 900 bar) is currently established. This requires valves that are also designed for this high pressure range. In this case, powerful regulating elements or actuators are often required to perform the movements against these pressures. Therefore, in a preferred embodiment of the invention, a hydrogen switching valve is used with pressure compensation for the valve piston (or armature in the case of a solenoid valve), which greatly reduces the regulating forces. This therefore means that lighter and more fragile actuators can be used. Therefore, in this embodiment of the invention, one or more overflow holes are provided in the housing and / or in the actuator, which allow the high-pressure hydrogen to reach the other side of the valve piston, whereby lower regulating forces are required. It is also possible to provide the piston or the armature with one or more longitudinal grooves. Pressure compensation at the armature end stops is particularly useful.

[0026] To ensure that the shut-off function for very high hydrogen pressures can be performed completely, the hydrogen switching valve and / or the purge valve can each be assigned a sealing valve seat. For example, a seat valve can be provided at the front stop of the actuator. The seat can be a ball seat or a flat valve seating surface. Sealing elements such as one or more O-rings, overmolded seats or overmolded valve slides can also be provided.

[0027] The inventors have realized that recirculation should not or need not occur during purging. Therefore, both functions can be controlled simultaneously with the single valve proposed herein, i.e., when recirculation is stopped, purging can be started. Then, when purging is finished, recirculation can be started again. Purging without recirculation has the advantage that gas with high nitrogen content is discharged first. There is no mixing with fresh hydrogen, which increases the overall efficiency.

[0028] In one embodiment, a stroke monitoring device is assigned to the purge valve. This monitoring device detects the triggering of the valve, for example by monitoring the valve stroke, the valve piston, or when using a ball of the ball stroke. This results in a functional monitoring of the purge (when the switching valve is activated) and a monitoring of the pressure relief valve function (when the switching valve is switched off). Thanks to the integrated multifunctionality, the switching function of the recirculation cutoff can also be checked in this way. The piston or ball stroke monitoring sensor system can be implemented, for example, by measuring a Hall sensor, a reed contact, or a contact resistance. The opening of the purge valve can also be monitored indirectly, for example, by measuring the pressure using a pressure sensor in the outlet or by monitoring the hydrogen in the outlet. The valve opening is then indicated by an increase in pressure or an increase in hydrogen content.

[0029] In a preferred embodiment, the recirculation loop shutoff valve provides pneumatic end position damping for one or both end positions in both stroke directions.

[0030] The shutoff device according to the invention can be made of any suitable material. The material must be able to withstand the mechanical loads and temperatures prevailing at the location. Metal or plastic is therefore recommended as the main material for the piston, housing and lines. An elastic material is recommended for the seals.

[0031] In the following, the present invention is described by way of example using preferred exemplary embodiments and with reference to the accompanying drawings, in which the features presented below can represent aspects of the invention both individually and in combination. [Brief description of the drawings]

[0032] [Figure 1] 1 shows a shutoff device according to the present invention on a hydrogen injection device in a fuel cell stack. [Diagram 2] 2 shows the interruption device of FIG. 1 in four different switching situations; [Diagram 3] 2 shows the interruption device of FIG. 1 in four different switching situations; [Figure 4] 2 shows the interruption device of FIG. 1 in four different switching situations; [Diagram 5] 2 shows the interruption device of FIG. 1 in four different switching situations; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] FIG. 1 shows a cut-off device according to the invention on a hydrogen injection device in a fuel cell stack with passive recirculation. The hydrogen injection device contains a hydrogen inlet 10, a recirculation gas inlet 12, and a jet pump 14 with a nozzle 16 and a nozzle needle 18. The jet pump 14 injects fresh hydrogen from the hydrogen inlet 10 through the nozzle 16. This hydrogen is under high pressure and therefore at high velocity, and conveys the recirculation gas from the recirculation gas inlet 12 and the recirculation loop 40 in the direction of the gas outlet 38 to the anode compartment of the stack, so that the passive recirculation continues. The gases mix in the suction chamber before the nozzle 16 and pass through a mixing tube and a diffuser to the gas outlet 38. The hydrogen control valve 32 is moved back and forth by a linear actuator with an electromagnet, thereby controlling the amount of fresh hydrogen supplied. A pressure sensor 36 measures the gas pressure in the anode compartment, thereby providing a measure of the amount of hydrogen required.

[0034] Located below the hydrogen injection device, but now integrated in the same housing, are the essential components of the shutoff device according to the invention for the recirculation loop 40, namely, the hydrogen switching valve 22 with the valve piston or slide 26, the recirculation loop shutoff valve 20 with the valve piston or slide 24, and the purge valve 44.

[0035] The hydrogen switching valve 22 is equipped with a linear actuator 28, e.g. an electromagnet, which is able to move the valve slide 26 back and forth via an armature 30. The valve slide 26 of the hydrogen switching valve 22 is pressed to the right by a restoring spring 34 against a right stop and closes, by means of its valve seat 48, the opening from the hydrogen inlet 10 to the circulation loop shut-off valve 20 (normally in the closed position). The hydrogen switching valve 22 is provided with two overflow holes next to the valve slide 26 to ensure pressure compensation.

[0036] To the right of the opening is the recirculation loop shutoff valve 20, whose valve slide 24 is pushed to the left by a restoring spring 42. In this left stop position, the line from the recirculation loop 40 to the stack is released and reaches the open position for normal operation (normally the open position). In FIG. 1, the valve slide 24 of the recirculation loop shutoff valve 20 is not shown in one of its two end positions, but in an intermediate position in which it closes the recirculation loop 40 between the recirculation gas inlet 12 and the stack. In the case of the valve slide 24 of the recirculation loop shutoff valve 20, two end position dampers are provided in the end stops, which preferably function pneumatically. Below the hole for the valve slide 24 of the recirculation loop shutoff valve 20 there are two longitudinal grooves 46, which allow the gas to flow slowly through the valve slide 24 and serve as an overflow hole. A tappet 60 is attached to the valve slide 24 and extends to the right in the direction of the purge valve 44 .

[0037] The purge valve 44 is located at the far right. It has a valve ball 46 that is pressed against a valve seat 52 by a spring 56. The purge valve 44 is arranged in a purge line 54 that leads from the recirculation loop 40 to an outlet 58 to the outside. At the same time, it is located directly in the vicinity of the recirculation loop shutoff valve 20, so that the tappet 60 can mechanically transmit the movement of the valve slide 24 to the ball 46. When the recirculation loop shutoff valve 20 closes, the valve slide 24 moves to the right to close the line of the recirculation loop 40 and, if it is far enough away, transmits this movement to the ball 46 via its tappet 60. This causes the tappet 60 to lift the ball 46 from its valve seat 52, thereby opening the purge valve 44. In this embodiment, the ball 46 of the purge valve 44 also has a surface that indicates the pressure in the line 40 (and thus in the stack) via the line 54, so that the purge valve 44 also acts as a pressure relief valve. If the pressure within the stack, loop 40 or line 54 increases beyond a preset level, the pressure will lift the ball 46 off its seat 52, allowing the excess pressure to escape to the outside via the outlet 58.

[0038] A stroke monitoring device 62 is positioned near the ball 46 to detect the position of the ball 46 and report it to the control system.

[0039] 2-5 show the interruption device of FIG. 1 in four different switching situations to explain the operation mode.

[0040] 2 shows the fail-safe positions of the three valves, namely the hydrogen switching valve 22, the recirculation loop shut-off valve 20 and the purge valve 44, i.e. their rest positions when all are de-energized. Since the linear actuator 28 is not actuated, the restoring spring 34 presses the valve slide 26 of the hydrogen switching valve 22 to the right end position, where the valve slide 26 closes the opening to the circulation loop shut-off valve 20. The hydrogen switching valve 22 is therefore closed. High pressure hydrogen gas cannot then reach the recirculation loop shut-off valve 20 from the hydrogen inlet 10.

[0041] The second restoring spring 42 urges the valve slide 24 of the recirculation shut-off valve 20 to its left end position, so that the valve slide 24 keeps the recirculation circuit 40 open. The recirculation loop shut-off valve 20 is therefore open, so that the recirculation gas can reach the hydrogen injection device and thus the stack from the recirculation gas inlet 12 upwards.

[0042] The purge valve 44 is closed (fail-safe). A spring 56 presses the ball 46 against the valve seat 52.

[0043] 3 shows three valves in different positions: hydrogen switch valve 22, recirculation loop isolation valve 20, and purge valve 44. Here, the linear actuator 28 is energized, pulling the valve slide 26 of the hydrogen switch valve 22 slightly to the left, so that the valve slide 26 opens the opening to the recirculation loop isolation valve 20. Thus, the hydrogen switch valve 22 is open, so that high pressure hydrogen gas can reach the recirculation loop isolation valve 20 from the hydrogen inlet 10.

[0044] This high pressure gas (or hydrogen supply pressure) pushes the valve slide 24 of the recirculation shut-off valve 20 to the right against the action of the spring 42, so that the valve slide 24 closes the recirculation loop 40. The recirculation loop shut-off valve 20 is therefore closed. Recirculated gas can no longer reach the hydrogen injection device and thus the stack from the recirculated gas inlet 12 upwards.

[0045] The purge valve 44 is still closed. The spring 56 presses the ball 46 against the valve seat 52.

[0046] 4 shows the three valves in further positions, namely, the hydrogen selector valve 22, the recirculation loop isolation valve 20, and the purge valve 44. Now, the linear actuator 28 is further energized, pulling the valve slide 26 of the hydrogen selector valve 22 slightly to the left against the action of the spring 34, so that the valve slide 26 leaves the opening to the recirculation loop isolation valve 20 open. Thus, the hydrogen selector valve 22 is open, so that high pressure hydrogen gas can reach the recirculation loop isolation valve 20 from the hydrogen inlet 10.

[0047] This high pressure gas (or hydrogen supply pressure) pushes the valve slide 24 of the recirculation loop isolation valve 20 further to the right against the action of the spring 42, so that the valve slide 24 holds the recirculation loop 40 closed. The recirculation loop isolation valve 20 is therefore closed. Recirculated gas can no longer reach the hydrogen injection device and thus the stack from the recirculated gas inlet 12 upwards.

[0048] At the same time, the valve slide 24 is pushed to the right sufficiently to open the purge valve 44 via its tappet 60. The purge valve 44 is open. Since the hydrogen on-off valve 22 is open, this pressure holds the valve 44 open. The leakage caused by the groove is compensated for by the supply of fresh hydrogen. The recirculation loop shut-off valve 20 and the purge valve 44 are open. Now, when the hydrogen switching valve 22 closes, the pressure in front of the valve slide is reduced by outflow via the groove or radial play. Depending on the size of the groove or radial play, the recirculation loop shut-off valve 20 opens more quickly or more slowly. The purge valve 44 closes at the same time as the valve slide moves.

[0049] FIG. 5 shows how the purge valve 44 acts as a pressure relief valve 44 .

[0050] As shown in FIG. 2, the hydrogen selector valve 22 is de-energized and closed.

[0051] No hydrogen supply pressure is applied to the left of valve slide 24 of recirculation loop isolation valve 20, so it is open as in FIG.

[0052] Excess pressure in the recirculation loop 40 reaches the purge valve 44 via a purge line 54, where the purge valve 44 acts as a pressure relief valve 44 and opens to release the excess pressure. [Explanation of symbols]

[0053] 10 Hydrogen inlet 12 Recirculation gas inlet 14 Jet pump 16 Nozzles 18 Nozzle needle 20 Recirculation Loop Shutoff Valve 22 Hydrogen switching valve 24 Recirculation Loop Shutoff Valve Slide 26 Hydrogen switching valve slide 28 Linear Actuator 30 Armature 32 Hydrogen control valve 34 Hydrogen switching valve return spring 36 Pressure Sensor 38 Gas outlet to stack 40 Recirculation loop from stack 42 Recirculation loop shutoff valve return spring 44 Purge valve / pressure relief valve 46 Purge valve ball 48 Hydrogen switching valve seat 52 Purge valve seat 54 Purge Line 56 Purge valve spring 58 Exit 60 Tappet 62 Stroke Monitoring Device

Claims

1. A shut-off device for a recirculation loop (40) in a fuel cell stack, comprising a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54), comprising a recirculation loop shut-off valve (20) which is switched by an upstream hydrogen switching valve (22) and which has an integrated purge valve (44) which is also designed as a pressure relief valve (44); Shut-off device, characterized in that the recirculation loop shut-off valve (20) is designed as a slide valve which mechanically operates the purge valve (44).

2. A shut-off device for a recirculation loop (40) in a fuel cell stack, comprising a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54), comprising a recirculation loop shut-off valve (20) which is switched by an upstream hydrogen switching valve (22) and which has an integrated purge valve (44) which is also designed as a pressure relief valve (44); A shutoff device, characterized in that the valve slide (24) of the recirculation loop shutoff valve (20) has a certain amount of leakage.

3. A shut-off device for a recirculation loop (40) in a fuel cell stack, comprising a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54), comprising a recirculation loop shut-off valve (20) which is switched by an upstream hydrogen switching valve (22) and which has an integrated purge valve (44) also designed as a pressure relief valve (44), A shut-off device, characterized in that said purge valve (44) is actuated by a mechanical connection, preferably a tappet (60).

4. A shut-off device for a recirculation loop (40) in a fuel cell stack, comprising a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54), comprising a recirculation loop shut-off valve (20) which is switched by an upstream hydrogen switching valve (22) and which has an integrated purge valve (44) which is also designed as a pressure relief valve (44), 2. A shut-off device, characterized in that the hydrogen switching valve (22) and the purge valve (44) are seat valves, and the purge valve (44) is preferably a check ball valve.

5. A shut-off device for a recirculation loop (40) in a fuel cell stack, comprising a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54), comprising a recirculation loop shut-off valve (20) which is switched by an upstream hydrogen switching valve (22) and which has an integrated purge valve (44) which is also designed as a pressure relief valve (44), A shut-off device, characterized in that a stroke monitoring device (62) is assigned to said purge valve (44).

6. A shut-off device for a recirculation loop (40) in a fuel cell stack, comprising a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54), comprising a recirculation loop shut-off valve (20) which is switched by an upstream hydrogen switching valve (22) and which has an integrated purge valve (44) which is also designed as a pressure relief valve (44), Shut-off device, characterized in that the recirculation loop shut-off valve (20) has pneumatic end position braking for one or both end positions.

7. The shutoff device according to any one of claims 1 to 6, characterized in that the hydrogen switching valve (22) is electrically controlled.

8. 7. The shutoff device according to any one of claims 1 to 6, characterized in that the hydrogen switching valve (22) and / or the recirculation loop isolation valve (20) and / or the purge valve (44) each have a restoring mechanism, preferably each have an integrated restoring spring (34, 42, 56).

9. Shut-off device according to any one of claims 1 to 6, characterized in that it is made substantially from metal or plastic.

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