Method for determining the actual actual pre-pressure of a diaphragm pressure expansion vessel

Abstract

The invention relates to a method for determining the current actual pre-pressure pIST of a diaphragm pressure expansion vessel (1) which has an interior with a known nominal volume VN, which is separated by a diaphragm (2) into a gas chamber (3) and a liquid chamber (4), wherein the filling volume of the liquid chamber (4) is unknown, wherein the gas chamber (3) of the diaphragm pressure expansion vessel (1) is connected to a testing device (8) and the pressure in the gas chamber (3) is changed by means of the testing device (8), wherein the testing device (8) first measures the current pressure p1 in the gas chamber (3), then a gas volume Vz with a pressure pz is supplied to the gas chamber (3) by the testing device (8), thereby generating a pressure increase in the gas chamber (3) to a pressure p2. It is provided that the actual pre-pressure pIST is calculated from the values ​​p1, p2, pz, VZ and VN as follows: pIST=p2VN⋅pZ⋅VZp2−p1.

Description

[0001] The invention relates to a method for determining the current actual pre-charge pressure p IST of a diaphragm pressure expansion vessel, which has an interior space with a known nominal volume VN, which is separated by a diaphragm into a gas and a liquid space, wherein the filling volume of the liquid space is unknown, wherein the gas space of the diaphragm pressure expansion vessel is connected to a test device and the pressure in the gas space is changed by means of the test device, wherein the current pressure p 1 in the gas space is first measured by the test device, then a gas volume V z with a pressure pz is supplied to the gas space by the test device and thereby a pressure increase in the gas space (3) to a pressure p 2 is generated, and a test device for carrying out this method.

[0002] Diaphragm expansion vessels are typically used in closed heating, cooling, domestic hot water, and solar thermal systems. The volume change caused by temperature fluctuations in the liquid heat transfer fluid is absorbed or released by a diaphragm expansion vessel. For this purpose, the diaphragm expansion vessel is internally divided into volume-varying gas and liquid chambers by an elastic diaphragm.

[0003] The pressure in the gas space of a diaphragm expansion vessel when it is not filled with the heat transfer fluid (e.g., at the time of installation before connecting the fluid space to the system's piping network) is generally called the pre-charge pressure. This pre-charge pressure must be adjusted to the specific system conditions, taking into account factors such as the static system height. This pre-charge pressure is essential for the proper functioning of a diaphragm expansion vessel.

[0004] During operation, the gas in the gas space, usually nitrogen, slowly diffuses through the membrane into the heat transfer fluid. As a result, the pre-charge pressure decreases over time, and gas must be added during maintenance to ensure the proper functioning of the diaphragm expansion vessel.

[0005] To check and, if necessary, correct the pre-charge pressure of a diaphragm expansion vessel, it has previously been necessary in practice to measure the current pre-charge pressure on a diaphragm expansion vessel that is depressurized on the fluid side and correct it if necessary. This requires disconnecting the diaphragm expansion vessel from the system and emptying the fluid chamber, which is time-consuming and inconvenient. For example, if water is used as the heat transfer fluid, the water drained for the pre-charge pressure test usually has to be drained and replaced with fresh drinking water, leading to an undesirable increase in resource consumption. Furthermore, it is disadvantageous that the system water should be replaced with fresh drinking water as little as possible to avoid oxygen ingress and scale formation in the system. Therefore, at least in larger systems, complex water treatment is required. If a water-glycol mixture is used as the heat transfer fluid (e.g.,In the case of solar thermal systems, the heat transfer fluid must be collected, pumped back into the system, and the system vented. Using a water-glycol mixture results in even greater testing effort.

[0006] To avoid these disadvantages, a method for measuring the actual pre-charge pressure of a diaphragm expansion vessel with an unknown liquid-side filling and with knowledge of the nominal volume of the diaphragm expansion vessel is known from DE 10 2016 012 700 B4. In this method, the diaphragm expansion vessel is connected to two controllable valves and a pressure transmitter via a connecting line. A volume of gas is released from the diaphragm expansion vessel into the ambient air via a flow meter or a measuring nozzle using a valve until the pressure measured at the pressure transmitter has decreased from the starting pressure to the final pressure of the measurement. The actual pre-charge pressure is then calculated using the measured values ​​obtained in this way and the known atmospheric pressure. Furthermore, a device suitable for carrying out this method for measuring the actual pre-charge pressure of a diaphragm expansion vessel is known from this document.Since the pre-charge pressure inevitably drops when gas is withdrawn from the diaphragm expansion vessel, it is usually necessary to refill the gas after the measurement procedure is complete. If the actual pre-charge pressure is very low, the measurement procedure is not applicable, as an insufficient volume of gas can be withdrawn.

[0007] From DE 43 20 383 A1 and DE 40 06 905 A1, a method with the features of the preamble of claim 1 is known.

[0008] The object of the invention is to create an improved solution for determining the current actual pre-pressure of a diaphragm pressure expansion vessel, independent of the actual pressure conditions in the diaphragm pressure expansion vessel, in which the diaphragm pressure expansion vessel does not have to be separated from the associated system and emptied.

[0009] This problem is solved according to the invention in a method of the type described above by calculating the actual pre-print p IST from the values ​​p 1 , p 2 , pz , V z and VN as follows. p IST = p 2 V N ⋅ p z ⋅ V Z p 2 − p 1 .

[0010] By introducing a defined volume of gas and the resulting pressure increase in the gas chamber of the diaphragm expansion vessel, it is possible to determine the current pre-charge pressure, independent of the actual pressure conditions within the vessel. No water needs to be drained from the diaphragm expansion vessel for this purpose. Before starting the measurement, it is advisable to shut off the water supply to the vessel to maintain a constant volume ratio between the gas and water chambers for the calculation and adjustment steps.

[0011] When determining the actual pre-charge pressure, any minor temperature differences that may occur and have little influence on the volume ratio are disregarded. However, they can also be taken into account through more complex calculations and temperature measurements. After connecting the test device, the pressure p1 in the gas chamber of the diaphragm expansion vessel is measured at the start of the test. In the next step, a known gas volume VZ at a known pressure pZ is added to the gas chamber, and the resulting pressure increase to a pressure p2 is measured. The amount of gas added, VZ, at the pressure pZ is precisely defined, which can be achieved in various ways.

[0012] From the known pressure values ​​and volumes, the actual pre-pressure p IST can be determined as follows: For isothermal changes of state and a constant number of gas particles (amount of gas), Boyle's and Mariotte's law applies: p ⋅ V = konstant

[0013] So: p IST ⋅ V N = p 1 ⋅ V 1 = p 2 ⋅ V 2

[0014] After the measurement begins, a gas volume VZ at a pressure pZ is introduced into the gas space of the diaphragm expansion vessel, which, however, cannot expand due to the compressibility of water. The pressure increases, but the gas volume remains constant; therefore: V 2 = V 1

[0015] The supply of the gas volume VZ at a pressure p Z is taken into account in (1) as follows: p IST ⋅ V N = p 1 ⋅ V 1 + p Z ⋅ V Z = p 2 ⋅ V 2

[0016] From (2) and (3): p Z ⋅ V Z = V 1 ⋅ p 2 − p 1 V 1 = V 2 = p z ⋅ V Z p 2 − p 1

[0017] From (3) and (5): p IST ⋅ V N = p 2 ⋅ p z ⋅ V Z p 2 − p 1

[0018] From (6): p IST = p 2 V N ⋅ p z ⋅ V Z p 2 − p 1 p IST: current actual pre-charge pressure (to be determined) VN: nominal volume of the expansion vessel (known) p 1: pressure in the gas chamber at the start of the measurement (measured) V 1: volume of the gas chamber at the start of the measurement (unknown) p 2: pressure in the gas chamber at the end of the measurement (measured) V 2: volume of the gas chamber at the end of the measurement (unknown) VZ: volume of gas supplied (known) p Z: pressure of the supplied gas volume (known)

[0019] Several methods are possible for the defined supply of a gas volume.

[0020] According to an initial design, the pressure in the gas space is increased by the test device to a predetermined pressure p 2 and the supplied gas volume V z is measured or determined.

[0021] According to a second embodiment, a predetermined gas volume VZ is supplied to the gas space by the test device, and the increased pressure p 2 in the gas space is then measured.

[0022] To solve the problem, a test device for determining the current actual pre-pressure p IST of a diaphragm pressure expansion vessel is also provided for carrying out the aforementioned procedure with a measuring chamber with pressure sensor, wherein the measuring chamber is connected to a connecting line for connecting to the gas space of the diaphragm pressure expansion vessel and to a gas supply device, wherein an electronic measuring and evaluation unit is provided which interacts with the pressure sensor and the gas supply device and is designed to carry out the aforementioned procedure.

[0023] It is advantageously provided that the gas supply device is a compressor or a piston pump. When using a compressor, the supplied gas volume is preferably determined via the compressor characteristic curve and the back pressure in the gas chamber. If the gas volume is supplied by a piston pump, the piston chamber is optionally pressurized either at ambient pressure or at a defined pressure. The supplied gas volume is determined via the number of piston strokes or via the piston stroke position and the back pressure of the gas chamber.

[0024] Alternatively, the gas supply device is a gas cartridge connected to a solenoid valve. The supplied gas volume is determined by measuring the switching times of the solenoid valve to the gas cartridge and by measuring the pressure in the gas cartridge and the back pressure in the gas chamber.

[0025] All the aforementioned embodiments of the gas supply device can optionally be equipped with a volume flow measuring unit and / or a nozzle, which increases the accuracy of the gas quantity measurement.

[0026] The invention is explained in more detail below with reference to the drawing. This drawing shows a simplified, non-scale schematic representation of the invention. Fig. 1 a diaphragm pressure expansion vessel with a first testing device, Fig. 2 a diaphragm pressure expansion vessel with a second testing device, Fig. 3 a diaphragm pressure expansion vessel with a third testing device and Fig. 4 a diaphragm pressure expansion vessel with a fourth testing device.

[0027] A diaphragm expansion vessel is generally designated by 1 in the drawings. It has an interior space with a known nominal volume VN, which is separated by a diaphragm 2 into a gas space 3 and a liquid space 4. The liquid space 4 is connected via a lockable connection 5 (e.g., with a cap valve, not shown) to a closed pipe network, also not shown, of a heating, cooling, domestic hot water, and solar thermal system. The current fill volume of the liquid space 4 is unknown.

[0028] The diaphragm expansion vessel 1 has a gas filling valve 6 connected to the gas space 3, to which a connecting line 7 of a test device generally designated 8 is connected. The test device 8 has a measuring chamber 9 with a pressure sensor 10 and optionally a temperature sensor 11, wherein the measuring chamber 8 is connected to the connecting line 7 for connection to the gas space 3 of the diaphragm expansion vessel 1 and to a gas supply device. In the exemplary embodiment, the gas supply device is as follows: Fig. 1The gas cartridge 13 is connected to a solenoid valve 12. A pressure regulator 14 is arranged between the gas cartridge 13 and the solenoid valve 12. The solenoid valve 12 is connected to a further pressure sensor 15 and establishes the connection from the gas cartridge 13 to the measuring chamber 9 in order to supply a gas volume Vz at a pressure pz to the measuring chamber 9, and thus to the gas space 3 of the diaphragm expansion vessel 1. The pressure pz is measured by the pressure sensor 15. The supplied gas volume Vz is determined via the switching times of the solenoid valve 12 to the gas cartridge 13 and by means of the pressure in the gas cartridge 13 measured by the pressure sensor 15 and the pressure in the measuring chamber 8, and thus in the gas space 3, measured by the pressure sensor 10. The test device 8 also has an electronic measuring and evaluation unit 16, which is connected to the pressure sensors 10, 15, the temperature sensor 11, the solenoid valve 12 and the pressure regulator 14.The electronic measuring and evaluation unit 16 is connected to a battery or a power supply unit. The temperature sensor 11 allows for compensation of the introduced volume.

[0029] To determine the current actual pre-charge pressure pIST of the diaphragm expansion vessel 1, the connection port 5 of the diaphragm expansion vessel 1 is first closed off, and the connection line 7 of the test device 8 is connected to the gas chamber 2 of the diaphragm expansion vessel 1 via the gas filling valve 6. The test device 8 then uses the pressure sensor 10 to measure the current pressure p1 in the measuring chamber 8, and thus in the gas chamber 3. Subsequently, the test device 8, controlled by the electronic measuring and evaluation unit 16, supplies a gas volume Vz at a pressure pz to the measuring chamber 8, and thus to the gas chamber 3, thereby increasing the pressure in the gas chamber 3 to a pressure p2. Finally, the actual pre-charge pressure pIST is calculated from the values ​​p1, p2, pz, VZ, and VN by the electronic measuring and evaluation unit 16 in the manner described above.

[0030] In Fig. 2Figure 1 shows a diaphragm pressure expansion vessel 1 with a second test device 8, which differs only in the design of the gas supply device; the reference numerals remain unchanged for identical parts. In this embodiment, the gas supply device is formed by a piston pump 17. When the gas volume is supplied to the measuring chamber 8 by the piston pump 17, the piston chamber is selectively pressurized either at ambient pressure or at a defined pressure. The supplied gas volume Vz is determined via the number of piston strokes or via the piston stroke position and the back pressure in the measuring chamber 8 and thus in the gas space.

[0031] In Fig. 3A diaphragm pressure expansion vessel 1 is shown with a third test device 8, which differs only in the design of the gas supply device; the reference numerals remain unchanged for identical parts. In this embodiment, the gas supply device is formed by a compressor 18. When using a compressor 18, the supplied gas volume Vz is preferably determined via the compressor characteristic curve and the back pressure in the measuring chamber 8 and thus in the gas space 3.

[0032] In Fig. 4A diaphragm pressure expansion vessel 1 is shown with a fourth test device 8, which differs from the aforementioned embodiments only in that an additional volume flow sensor 19 is provided in the connecting line 7 to determine the supplied gas volume Vz, which is connected to the electronic measuring and evaluation unit 16. The gas supply device can optionally be a gas cartridge 13, a piston pump 17, or a compressor 18.

[0033] Example: A diaphragm pressure expansion vessel 1 with the following values ​​was tested according to the measurement procedure described above: VN = 33.73 l lp 1 = 1.355 bar p 2 = 1.455 bar p Z = 2.054 bar From (5) we get: V 1 = V 2 = 33.357 l From (7) we get: p IST = 1.439 bar

[0034] The value determined for p IST is greater than the pressure p 1 at the start of the measurement, since the pressure was increased by the supply of the gas volume VZ; therefore, the determined pre-pressure p IST is the one at the end of the measurement.

[0035] If the determined actual pre-charge pressure is below the target pre-charge pressure of the diaphragm expansion vessel 1, additional gas volume can then be added using the test device 8, if necessary, to adjust the target pre-charge pressure based on the determined actual pre-charge pressure p ACTUAL: P 2 soll = P VDsoll ⋅ V 1 V 1 PVDsoll: Target pre-pressure; p2soll: Pressure to be set in the gas chamber at the end of the measurement

[0036] By generating the target pressure p2 in the sealed diaphragm expansion vessel 1, the target pre-charge pressure pVD is restored. The connection port 5 of the diaphragm expansion vessel 1 can then be unlocked.

[0037] Since the nominal volume VN and the volume V2 in gas space 3 are determined, the current volume in liquid space 4 can also be determined. If this volume is too large, because in practice liquid is frequently added without determining the current pre-charge pressure, it is necessary to drain some liquid to allow it to expand.

[0038] For this purpose, a paddle wheel sensor or other water flow meter with a solenoid valve for opening and closing is electrically connected to the test device 8. The water flow meter with the solenoid valve is connected to the cap valve on the connection port 5 of the diaphragm expansion vessel 1 to allow for the controlled release of a defined quantity of fluid. The solenoid valve then closes again once the target fluid quantity has been reached. Since fluid is often added when the system pressure is too low, an adjustment of the fluid quantities may be necessary during maintenance. This is because the system pressure is maintained by adjusting the gas pressure in the gas cushion, and the diaphragm expansion vessel 1 returns to its target fill level operating range of 20–60%.

[0039] Connectivity to a maintenance assistant (app) may be provided. Vessel maintenance can be combined with other maintenance tasks. Consequently, a maintenance log can be accessed later, possibly online.

[0040] Optionally, a vessel barcode or serial number can also be included to validate the vessel volume (and, if applicable, the year of manufacture).

[0041] Integrated "machine learning" can also be provided to continuously optimize accuracy through experience (data collection / connectivity to the maintenance assistant). Reference symbol list:

[0042] 1 Membrane expansion vessel 2 Membrane 3 Gas chamber 4 Liquid chamber 5 Connection fitting 6 Gas filling valve 7 Connection line 8 Test device 9 Measuring chamber 10 Pressure sensor 11 Temperature sensor 12 Solenoid valve 13 Gas cartridge 14 Pressure regulator 15 Pressure sensor 16 Electronic measuring and evaluation unit 17 Piston pump 18 Compressor 19 Flow sensor

Claims

1. A method for determining the current actual pre-charge pressure pIST of a diaphragm pressure expansion vessel (1), which has an interior of known nominal volume VN, which is separated by a diaphragm (2) into a gas chamber (3) and a liquid chamber (4), wherein the filling volume of the liquid chamber (4) is unknown, wherein the gas chamber (3) of the diaphragm pressure expansion vessel (1) is connected to a test device (8) and the pressure in the gas chamber (3) is varied by means of the test device (8), wherein the current pressure p1 in the gas chamber (3) is first measured by the test device (8), subsequently a gas volume Vz at a pressure pz is supplied by the test device (8) to the gas chamber (3), thereby generating a pressure increase in the gas chamber (3) to a pressure p2, characterized in that the actual pre-charge pressure pIST is calculated from the values p1, p2, pz, Vz and VN as follows: P IST = p 2 V N ⋅ p z ⋅ V Z p 2 − p 1 2. The method according to claim 1, characterized in that the pressure in the gas chamber (3) is increased by the test device (8) to a predefined pressure p2 and the supplied gas volume Vz is measured or determined.

3. The method according to claim 1, characterized in that a predefined gas volume Vz is supplied by the test device (8) to the gas chamber (3), and the increased pressure p2 in the gas chamber (3) is subsequently measured.

4. A test device for determining the current actual pre-charge pressure pIST of a diaphragm pressure expansion vessel (1) for carrying out the method according to one or more of claims 1 to 3, having a measuring chamber (9) with a pressure sensor (10), wherein the measuring chamber (9) is connected to a connection line (7) for connection to the gas chamber (3) of the diaphragm pressure expansion vessel (1) and to a gas supply device, wherein an electronic measurement and evaluation unit (16) is provided which cooperates with the pressure sensor (10) and the gas supply device and is configured to carry out the method according to one or more of claims 1 to 3.

5. The test device according to claim 4, characterized in that the gas supply device is a compressor (18) or a piston pump (17).

6. The test device according to claim 4, characterized in that the gas supply device is a gas cartridge (13) connected to a solenoid valve (12).

7. The test device according to one or more of claims 4 to 6, characterized in that the electronic measurement and evaluation unit (16) is connected to a rechargeable battery or a power supply unit.

8. The test device according to one or more of claims 4 to 7, characterized in that it is configured for attachment to a diaphragm pressure expansion vessel (1).

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