Device for operating non-explosion-proof equipment in a potentially explosive atmosphere

Abstract

The invention relates to a device for operating non-explosion-proof equipment in a potentially explosive atmosphere, comprising a pressurized housing (1) designed to accommodate the non-explosion-proof equipment (2), a purge gas inlet (3) arranged upstream of the housing (1) through which a protective gas (4) can be supplied to the housing (1) under overpressure, and a purge gas outlet (7) arranged downstream of the housing (1) through which the protective gas (4) can be discharged from the housing (1). For the discharge of the protective gas (4), an outlet valve (8) with a valve seat (16) and a valve body (30) is arranged in the purge gas outlet (7). The valve body (30) is connected to the first end of a guide axis (31) which is slidably mounted in a through bore (21) in the valve seat (16) along the valve axis (15) so that the valve body (30) is axially adjustable between a closed position and an open position.By means of a spring element (34), the valve body (30) is biased against the valve seat (16) in the closed position. To achieve efficient and gentle operation with moderate equipment costs, the invention proposes that a baffle element (32) be attached to the opposite second end of the guide axis (31) and that a control housing (25) with a working chamber (28) be connected to the valve seat (16), wherein the baffle element (32) is arranged within the working chamber (28) and without contact with the control housing (25). Furthermore, the control housing (25) has a connection (27) to which a control line (9) is connected for supplying the working chamber (28) with a working fluid (29), via which the working chamber (28) and the baffle element (32) arranged therein can be pressurized with the working fluid (29) from the control line (9).

Description

field of technology

[0001] The invention relates to a device for operating non-explosion-proof equipment in a potentially explosive environment according to the preamble of claim 1. State of the art

[0002] The overpressure enclosure (Ex-p) type of ignition protection is used for operating non-explosion-proof electrical equipment in potentially explosive atmospheres. The principle of this type of ignition protection is based on supplying an ignition-protective gas to an enclosure and maintaining it under constant overpressure relative to the surroundings, so that the ingress of explosive gas mixtures into the interior of the enclosure is impossible, or sufficient dilution is always present to prevent an ignitable atmosphere.

[0003] According to standard IEC 60079-2:2014, Explosive atmospheres - Part 2: Protection of equipment by pressurized enclosure, the enclosure must be purged of explosive gases during a pre-purge phase before the electrical equipment is put into operation. The pre-purge phase is considered complete when purge gas has flowed from the enclosure through the purge gas outlet for a specific minimum duration or in a specific minimum quantity. In the subsequent operating phase, different operating modes can be used, such as the "compensation for leakage losses" mode, in which, with the purge gas outlet closed, only the purge gas loss caused by leaks is compensated for, or the "continuous purge" mode, in which a release point for explosive gases is located within the enclosure, so that continuous purging dilutes the explosive gas.

[0004] Especially during the pre-rinse phase and in the transition to the operating phase, pressure fluctuations and pressure peaks occur in pressurized housings, which, depending on the size of the housing, lead to considerable stresses on the housing and must be taken into account through additional design effort.

[0005] From DE 44 18 158 A1, a device is known whose housing has a proportional valve at the purge gas inlet and a flow meter and a shut-off valve at the purge gas outlet. During the pre-purge phase, with both the proportional and shut-off valves open, the purge gas quantity is determined by integrating the flow rate over time. During the operating phase, with the shut-off valve closed, the overpressure in the housing is regulated by means of the proportional valve. This device successfully avoids excessive pressure loads on the housing during both the pre-purge and operating phases while simultaneously reducing the required amount of purge gas.

[0006] A further development of the device described above is the subject of DE 10 2008 024 836 B3, in which a proportional valve is arranged in both the purge gas inlet and the purge gas outlet. The proportional valve in the purge gas inlet is controlled in a first control loop as a function of the differential pressure in the housing, while the proportional valve in the purge gas outlet is controlled in a second control loop as a function of the purge gas flow rate at the outlet, which is determined by means of a flow meter. Through the interaction of the two control loops, such a device can be optimally adapted to the specific requirements of the respective application.

[0007] A simplified device is known from DE 103 13 203 A1. This patent proposes applying a purge pressure during the pre-purge of the housing that is greater than the opening pressure of the outlet valve in the purge gas outlet. This ensures that the outlet valve is open when the purge pressure is reached and that air exchange occurs via the open outlet valve. A flow meter in the purge gas outlet is unnecessary with this solution.

[0008] EP 3 772 048 A1 describes a pressurized enclosure with a housing connected to a purge gas source via a purge gas inlet, an inlet valve arranged between the purge gas source and the purge gas inlet, a pressure gauge or pressure switch monitoring the internal pressure in the housing, a control device for controlling the inlet valve to maintain a set internal pressure in the housing, a flow meter between the purge gas source and the purge gas inlet measuring the purge gas flow, an evaluation device for predicting the purge gas flow with regard to exceeding a threshold value, and a purge gas outlet leading from the housing. An outlet valve can be integrated into the purge gas outlet, which is closed during normal operation and only open during the purge process to purge the housing with a required minimum quantity of purge gas before commissioning or after malfunctions.

[0009] Furthermore, DE 37 25 995 C2 describes a purge gas filter for separating solid components from a purge gas. The purge gas filter has a filter housing for receiving a filter element mounted on a filter holder, wherein the hollow cylindrical filter housing has an annular projection on its inner wall extending transversely to the flow direction of the purge gas. One end face of this projection has an annular sealing surface against which a disc-shaped filter holder is pressed by the action of a spring element. Summary of the invention

[0010] Against this background, the object of the present invention is to provide a device of the type described above with a view to efficient and at the same time gentle operation with moderate equipment costs.

[0011] This problem is solved by a device having the features of claim 1.

[0012] Advantageous further training opportunities arise from the sub-requirements.

[0013] The solution according to the invention is based on the idea that the same outlet valve is used for both the pre-rinse phase and the operating phase, wherein the opening pressure for the outlet valve during the pre-rinse phase is generated independently of the overpressure inside the housing and the opening pressure for the outlet valve during the operating phase depends on the overpressure inside the housing.

[0014] By generating the opening pressure for the outlet valve separately, it is no longer necessary to wait for the opening pressure of the outlet valve to be reached inside the housing before starting the pre-purge phase. Instead, the outlet valve can be pressurized with sufficient opening pressure immediately, thus starting the pre-purge phase earlier. Simultaneously, the high pressure generated causes the outlet valve to open fully immediately after pressurization, allowing for maximum purge gas flow. In this way, it is possible to begin the pre-purge phase at the earliest possible time and execute it with the greatest possible purge gas flow through the purge gas outlet. Each of these measures, individually and especially both together, shorten the pre-purge phase and thus enable the device to be operational more quickly.

[0015] Since the opening pressure for the outlet valve during the pre-rinse phase is not generated by the overpressure inside the housing, no pressure spikes occur that regularly arise when overcoming the opening pressure of the outlet valve. The immediate opening of the outlet valve counteracts an excessively high build-up of overpressure. Therefore, the stresses on the housing due to overpressure during the pre-rinse phase are comparatively low in a device according to the invention, allowing the pre-rinse phase to be carried out more gently. The lower pressure forces acting on the housing allow for a less complex housing design.

[0016] During operation, however, the overpressure inside the housing is responsible for opening the outlet valve when the maximum permissible overpressure is exceeded. The sensitive response of the outlet valve at the significantly lower overpressures compared to the pre-rinse phase is maintained, thus preserving the operational reliability of a device according to the invention.

[0017] Since the same inlet valve is used in both the pre-rinse and operating phases, the aforementioned advantages can be achieved with comparatively little equipment effort. The invention is therefore also characterized by exceptional cost-effectiveness in this respect.

[0018] Advantageously, the control housing is cylindrical with a longitudinal axis coaxial to the valve axis, resulting in a compact design of the exhaust valve and a force acting along the valve axis to open the exhaust valve. The latter is further enhanced by the fact that the impact surface of the impact element is orthogonal to the valve axis or guide axis.

[0019] To prevent the baffle element from hindering adjustment of the valve body in or against the force of the spring element during operation, which would result in a higher force being required to open the exhaust valve, the baffle element and the control housing preferably maintain a clear distance perpendicular to the valve axis, thereby creating a circumferential gap between the baffle element and the control housing. In an advantageous embodiment of the invention, the clear width of the gap is less than 10% of the parallel width of the working chamber and is preferably in a range between 0.5% and 3%.

[0020] In the unintended event that a brief contact between the control housing and the impact element should occur during adjustment of the valve body, the impact element is advantageously made entirely or at least on its circumference of a material with a low coefficient of friction in order to avoid transmitting any significant disruptive forces through the contact.

[0021] Furthermore, the most unimpeded movement of the valve body is achieved by providing, according to an advantageous embodiment of the invention, that the working chamber has one or more passages for venting the working chamber downstream of the impact element.

[0022] To further reduce the technical complexity of the equipment, it is advantageous to use the purge gas supplied to the device as the working fluid. For this purpose, the control line is advantageously supplied with purge gas from the purge gas inlet.

[0023] To monitor or detect the purge gas flow rate in the purge gas outlet, a flow measuring device or flow monitor is integrated into the purge gas outlet upstream of the outlet valve in a further development of the invention. This ensures that the working fluid, which only enters the purge gas outlet in the area of ​​the outlet valve, does not distort the actual purge gas volume.

[0024] The flow measuring device or flow monitor advantageously comprises a measuring orifice and a device for detecting the differential pressure at the measuring orifice, which leads to particularly accurate purge gas flow values.

[0025] Without limiting ourselves to this, the invention will below be explained in more detail with reference to an embodiment shown in the drawing, whereby further features and advantages of the invention will become apparent. Brief description of the drawings

[0026] It shows Fig. 1 a device according to the invention in schematic representation, Fig. 2 a longitudinal section through the purge gas outlet of the in Fig. 1 device shown, Fig. 3 in a sectional oblique view the in Fig. 2 purge gas outlet shown with the outlet valve closed during the operating phase, Fig. 4 in a sectional oblique view that in Fig. 3. Outlet valve shown in open position during the pre-rinse phase, Fig. 5 the course of the overpressure according to the invention p Erf and the state of the art p SdT in the housing during the pre-rinse phase and operating phase, and Fig. 6 the course of the purge gas flow through the purge gas outlet according to the invention Q Erf and the state of the art Q SdT during the pre-rinse phase and operating phase. Description of the embodiments

[0027] In Fig. Figure 1 shows a schematic representation of a device according to the invention. The device has a housing 1 in which a non-explosion-proof electrical device 2 is enclosed. In order to be able to operate the electrical device 2 in a potentially explosive atmosphere, the housing 1 is protected against the ingress of explosive gas mixtures into the interior of the housing according to the type of ignition protection known as pressurised enclosure (Ex-p).

[0028] The overpressure enclosure (Ex-p) type of ignition protection is designed to prevent the formation of an explosive atmosphere inside the enclosure 1 during operation of the device (operating phase) by maintaining overpressure and, if necessary, purging the enclosure 1 to dilute ignitable gas mixtures. Depending on the specific application and the existing explosion protection zone, pre-purging the enclosure 1 with purge gas 4 may be necessary before commissioning the device 2 in order to remove any ignitable gas mixture present in the enclosure 1 (pre-purge phase).

[0029] For pressurization, the housing 1 has a purge gas inlet 3, through which purge gas 4, for example inert gas or air, is supplied to the housing 1 under pressure from a gas storage container (not shown). An inlet valve 5 is arranged in the purge gas inlet 3, which controls the flow of purge gas 4. While not limited to this, in this case the inlet valve 5 is a digital valve, it could also be a proportional valve. Downstream of the inlet valve 4, a throttle valve 6 is connected, which limits the pressure of the purge gas 4 flowing into the housing 1.

[0030] On the opposite side of the housing 1 is a purge gas outlet 7, through which excess or harmful purge gas 4 is discharged from the housing 1 during the pre-purge and operating phases. An outlet valve 8 located in the purge gas outlet 7 controls the purge gas 4 leaving the housing 1. The outlet valve 4 is the subject of the Fig. 2, Fig. 3 to Fig. 4 and is described in more detail there.

[0031] To actuate the outlet valve 8, a control line 9 branches off in the purge gas inlet 7 between the inlet valve 5 and the throttle valve 6, and subsequently connects to the outlet valve 8. The purge gas 4 flowing through the control line 9 to the outlet valve 8 is therefore under a significantly higher pressure than the pressure present inside the housing 1. For example, the pressure in the control line is in the bar range, while the overpressure inside the housing during the pre-purge and operating phases is in the millibar range.

[0032] Furthermore, a flow meter 10 is integrated into the purge gas outlet 7 upstream of the outlet valve 4. This meter measures the instantaneous purge gas flow rate in order to determine the purge gas quantity based on the measured values. A flow monitor can also be used instead of the flow meter 10. This monitor monitors the purge gas flow rate with regard to a minimum value and sends a signal if the flow rate falls below this minimum.

[0033] To monitor the pressure inside the housing 1 relative to the ambient pressure outside the housing 1, the device also has a differential pressure measuring device 11.

[0034] The measured values ​​obtained from the flow measuring device 10 and the differential pressure measuring device 11 are fed to a measuring and control device 12, which is symbolized by the dashed lines 13. The measuring and control device 12 consists, for example, of a microcontroller that processes the received data and, based on this, outputs control signals to the inlet valve 5, which is represented by line 14.

[0035] The design and function of the exhaust valve 8 are derived from the Fig. 2, Fig. 3 to Fig. 4 more closely, whereby the Fig. 2 and Fig. 3 shows the outlet valve 8 in a closed position, as is predominantly the case, for example, in the "compensation for leakage losses" operating mode during the operating phase. In contrast, shows Fig. 4. The outlet valve 8 is in the open position during the pre-rinse phase. In the Fig. 2, Fig. 3 to Fig. 4 is the valve axis marked with reference numeral 15 and in the present embodiment coincides with the longitudinal axis of the purge gas outlet 7.

[0036] The essential component of the exhaust valve 8 is a disc-shaped valve seat 16 with an outer ring section 17, the outer circumference of which connects positively and gas-tightly to the circular inner circumference 18 of the purge gas outlet 7. The axial center of the valve seat 16 is formed by a bearing disk 19, which has a cylindrical base 20 on the upstream side of the exhaust valve 8 that runs coaxially around the valve axis 15, giving the bearing disk 19 a greater axial thickness than the ring section 17. The bearing disk 19 has a through-bore 21 coaxial with the valve axis 15, around which several axially parallel passages 22 are grouped.

[0037] Three radial struts 23, arranged at uniform circumferential intervals, extend from the ring section 17 to the bearing disk 19 to hold it in the valve axis 15. Free areas remain between the radial struts 23, the ring section 17, and the bearing disk 19, forming openings 24 for the passage of purge gas 4 when the exhaust valve 8 is open.

[0038] On the upstream side of the exhaust valve 8, there is also a hollow cylindrical control housing 25, the longitudinal axis of which runs coaxially with the valve axis 15. The outer circumference of the control housing 25 corresponds in shape and diameter to the outer circumference of the bearing disc 19, and the inner circumference of the control housing 25 corresponds in shape and diameter to the outer circumference of the base 20, so that one end of the control housing 25 can be slid or screwed onto the base 20 for connection to the valve seat 16. The opposite end of the control housing 25 forms a thick-walled, frustoconical end wall 26, the pointed end of which faces against the flow direction. The end wall 26 has an axially penetrating connection bore 27, to which the control line 9 connects.

[0039] The control housing 25, together with the bearing disk 19 and the end wall 26, forms a cylindrical working chamber 28, which can be supplied with a working fluid 29 from the control line 9 via the connection bore 27. In the present embodiment, the working fluid 29 corresponds to the purge gas 4, which is branched off in the purge gas inlet 3 upstream of the throttle valve 6 (see figure). Fig. 1) The working fluid 29 can escape from the working chamber 28 via the passages 22 leading from the working chamber 28.

[0040] In the present embodiment, the valve body 30 of the exhaust valve 8 is formed by a circular sealing disc with a planar sealing surface, although this is not the only possible configuration. The valve body can also have a spherical or conical sealing surface, or be formed by flaps or a diaphragm.

[0041] The valve body 30 is rigidly mounted with a central receiving bore on the downstream first end of a rod-shaped guide shaft 31. The guide shaft 31 extends through the through-bore 21 of the bearing disk 19, in which it is axially displaceable. The upstream second end of the guide shaft 31 thus projects axially into the working chamber 28 and carries at its second end a baffle element 32 in the form of a baffle disc, oriented orthogonally to the guide shaft 31. The baffle element 32 is therefore located within the working chamber 28 and is adapted to its geometry; that is, the outer circumference of the baffle disc 32 follows the inner circumference of the working chamber 28 while maintaining a constant annular gap 33 around the circumference. The annular gap 33 ensures that the relative movement between the baffle disc 32 and the control housing 25 does not induce any additional resistance when the valve body 30 switches between the closed and open positions.

[0042] A spring element 34, pre-tensioned under pressure, is slid onto the guide shaft 31 between the impact element 32 and the bearing disk 19. This spring element pre-tensions the valve body 30 against the valve seat 16, so that the exhaust valve 8 is held in the closed position by the spring element 34, or returned to this position, as long as no external forces act on the valve body 30. The length of the guide shaft 31 is dimensioned such that, in the closed position, the impact element 32 is located in the area of ​​the end wall 26 of the control housing 25. In the open position, however, the impact element 32 is brought close to the bearing disk 19 by compressing the spring element 34. Due to the rigid coupling of the valve body 30 and the impact element 32 by the guide shaft 31, any movement of the impact plate 32 is transmitted directly to the valve body 30 and vice versa.

[0043] The operation of a device according to the invention is described below with additional reference to the Fig. 5 and Fig. 6 explains in more detail the time course of the differential pressure p Erf between the inside of the housing and the environment, as well as the purge gas flow rate Q Erf The time t0 corresponds to the time the device is switched on, the time t1 to the beginning of the pre-rinse phase, and the time t2 to the beginning of the operating phase.

[0044] After the device is switched on at time t0, all system components are initialized before the device commences operation at time t1. This operation begins with a pre-purge of the housing 1 with air or a protective gas for a predetermined purge duration or purge volume. For this purpose, the measuring and control unit 12 sends a control signal to the inlet valve 5 to open it. Purge gas 4, which is pressurized with purge gas 4 from a purge gas reservoir, enters the housing 1 at reduced pressure via the throttle valve 6 through the purge gas inlet 3. Simultaneously, purge gas 4, at a comparatively higher pressure, is diverted as working fluid 29 upstream of the throttle valve 6 and fed via the control line 9 to the outlet valve 8, where it flows into the working chamber 28 of the control housing 25 at a high pressure of, for example, 2 bar.

[0045] In the working chamber 28, the working fluid 29 impacts the impact element 32 head-on and presses it against the force of the spring element 34 and under its compression in the direction of the bearing disk 19. The axial movement is transmitted via the guide axis 31 to the valve body 30, which, upon reaching the open position, maximally releases the openings 24 so that purge gas 4 can be discharged from the interior of the housing 1 through the purge gas outlet 7.

[0046] Due to the continuous supply of purge gas 4 via the purge gas inlet 3, the minimum pressure p required for pre-purge builds up in the housing 1 from time t1. v The differential measuring device 11 registers the pressure and reports it to the measuring and control device 12. From this point on, the pre-rinse phase begins, during which the outlet valve 8 is in the Fig. The working position shown in Figure 4 is as follows. The working fluid 29 flowing into the working chamber 28 holds the valve body 30 in the open position by continuously flowing over the baffle element 32, whereby the baffle element 32 is surrounded by flow in the region of the annular gap 33. On the outflow side of the baffle element 32, the working fluid escapes from the working chamber 28 via the passages 22 and mixes with the purge gas 4 from inside the housing.

[0047] The purge gas flow exiting the housing 1 through the purge gas outlet 7 during the pre-purge phase is detected by the flow meter 10, and the corresponding measured values ​​are transmitted to the measuring and control unit 12. This unit monitors that, on the one hand, the required minimum pressure is not undershot during the pre-purge phase and, on the other hand, that sufficient purge of the housing 1 is ensured. The latter is achieved by monitoring a minimum purge duration while maintaining a minimum overpressure inside the housing or by integrating the purge gas flow rate at the purge gas outlet 8 over the time until the required purge gas volume is reached.

[0048] To end the pre-purge phase, the measuring and control device 12 gives a control signal to close the inlet valve 5, so that only the amount of purge gas 4 required to maintain the minimum overpressure in the housing 1 during the operating phase is supplied.

[0049] Closing the inlet valve 5 causes a pressure drop in the control line 9, resulting in the cessation of the flow of working fluid 29 to the impact element 32 and thus the actuating force exerted by the working fluid 29 on the impact element 32. Consequently, the restoring force of the spring element 34 predominates, pressing the valve body 30 against the valve seat 16 and closing the outlet valve 8.

[0050] The operating phase begins with the closing of the outlet valve 8, which is in the Fig. 5 and Fig. 6 corresponds to time t2. The outlet valve 8 is in the closed position as shown in the illustration. Fig.3. Only when the maximum overpressure inside the housing is exceeded, which is significantly lower compared to the pre-rinse phase, is the opening pressure of the outlet valve 8 reached. The pressure acting on the valve body 30 causes the outlet valve 8 to open briefly in order to reduce the overpressure.

Claims

[1] Device for operating non-explosion-proof equipment in a potentially explosive atmosphere - with a pressurised enclosure (1) designed to hold a non-explosion-proof device (2), - with a purge gas inlet (3) arranged upstream of the housing (1), through which a protective gas (4) can be supplied to the housing (1) under overpressure, - with a purge gas outlet (7) arranged downstream of the housing (1), through which the protective gas (4) can be drained from the housing (1), wherein - in the purge gas outlet (7) for the discharge of the protective gas (4) an outlet valve (8) is arranged with a valve seat (16) and a valve body (30), wherein the valve body (30) is connected to the first end of a guide axis (31) which is slidably mounted in a through bore (21) in the valve seat (16) along the valve axis (15), so that - the valve body (30) is axially adjustable between a closed position and an open position, wherein - the valve body (30) is pre-tensioned in the closed position by a spring element (34) against the valve seat (16), characterized by , that - a shock element (32) is attached to the opposite second end of the guide axis (31) and - a control housing (25) with a working chamber (28) is connected to the valve seat (16), wherein - the impact element (32) is arranged inside the working chamber (28) and without contact with the control housing (25), and wherein - the control housing (25) has a connection (27) to which a control line (9) is connected for supplying the working chamber (28) with a working fluid (29), - via which the working chamber (28) and the impact element (32) arranged therein can be pressurized with the working fluid (29) from the control line (9). [2] Device according to claim 1, characterized by , that the control housing (25) is cylindrical and the longitudinal axis of the control housing (25) is aligned in the adjustment direction of the valve body (30). [3] Device according to claim 2, characterized by , that the control housing (25) is circular cylindrical in shape. [4] Device according to claim 2 or 3, characterized by , that the longitudinal axis of the control housing (25) is aligned coaxially to the valve axis (15) in the adjustment direction of the valve body (30). [5] Device according to any one of claims 1 to 4, characterized by , that the impact element (32) has an impact surface running orthogonally to the longitudinal axis of the guide axis (31). [6] Device according to claim 5, characterized by , that the impact surface of the impact element (32) has a circular circumference. [7] Device according to any one of claims 1 to 6, characterized by, that the impact element (32) is formed entirely or at least around its circumference from a material with a low coefficient of friction. [8] Device according to any one of claims 1 to 7, characterized by , that the control housing (25) and the circumference of the impact element (32) are arranged at a clear distance from each other to form a circumferential gap (33). [9] Device according to claim 8, characterized by , that the width of the gap (33) is less than 10% of the straight clear width of the working chamber (28). [10] Device according to claim 9, characterized by , that the width of the gap (33) lies in a range between 0.5% and 3% of the straight clear width of the working chamber (28). [11] Device according to any one of claims 1 to 10, characterized by , that the control housing (25) has one or more passages (22) through which the working fluid (29) can escape from the working chamber (28) into the purge gas outlet (7) and / or the environment. [12] Device according to any one of claims 1 to 11, characterized by , that the valve body (30) has a disc-shaped, conical or spherical shape or is formed by a diaphragm or flaps. [13] Device according to any one of claims 1 to 12, characterized by , that the control line (9) is fluidically connected to the line for the supply of protective gas (4) into the purge gas inlet (3) and the working fluid (28) is formed from the protective gas (4). [14] Device according to any one of claims 1 to 13, characterized by , that a flow measuring device (10) or a flow monitor is arranged in the purge gas outlet (7) upstream of the outlet valve (8).

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