A gaseous pressure measuring isolator for a tank storage and handling facility

Abstract

The present application relates to a kind of tank type storage and transport equipment gas phase pressure measurement isolator, including tank body, top cover, tank body is cooperated with top cover and forms sealed chamber, and sealed chamber is filled with isolation liquid;Partition is provided in sealed chamber, and partition divides sealed chamber into gas inlet area and pressure measurement area, and the gap is left in the bottom of partition and the bottom of sealed chamber, so that gas inlet area is communicated with pressure measurement area, and the top of partition is higher than the liquid level of isolation liquid;Gas inlet is provided on the tank body corresponding to gas inlet area;Pressure measurement port is provided on the tank body corresponding to pressure measurement area;Perforated adsorption block is provided above the isolation liquid in gas inlet area, and the adsorbent is contained in perforated adsorption block;By being provided with partition in sealed chamber, it is divided into gas inlet area and pressure measurement area, and perforated adsorption block is set in gas inlet area, and corrosive component is actively absorbed and neutralized by adsorbent, so that the gas reaching isolation liquid has basically removed corrosiveness, reduce the probability of isolation liquid being contaminated, prolong the service life of isolation liquid and the maintenance cycle of pressure sensor.

Description

Technical Field

[0001] This invention relates to the field of pressure testing technology, and in particular to a gas phase pressure measurement isolator for tank storage and transportation equipment. Background Technology

[0002] Tank storage and transportation equipment (including tank trucks, tank containers, and storage tanks) is widely used in the chemical and hazardous materials transportation fields. Measuring the gas phase pressure of the medium inside the tank is a crucial aspect of safety management. Currently, pressure sensors are typically installed directly at the flange opening or gas phase valve opening on the top of the tank. The pressure-sensing device is in direct contact with the gas inside the tank, enabling real-time monitoring of the gas phase pressure.

[0003] However, when highly corrosive gaseous media (such as hydrogen chloride, ammonia, acid mist, etc.) are stored in the container, these corrosive gases can directly corrode the pressure sensor's sensing element, leading to sensor damage and failure, and resulting in high maintenance costs. To address this problem, existing technologies propose using an isolating liquid to isolate the pressure sensor from the corrosive gases. This involves using an isolating liquid filled in a sealed container to conduct gas pressure and prevent direct contact between the corrosive gases and the sensor. However, in this solution, the corrosive gases remain in direct contact with the isolating liquid, continuously contaminating and corroding it, causing the isolating liquid to deteriorate and fail, and thus failing to fundamentally protect the long-term stable operation of the pressure sensor. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a gas phase pressure measurement isolator for tank storage and transportation equipment. By setting a porous adsorption block in the air inlet area, the probability of the isolating liquid being contaminated by corrosive gases is reduced, the service life of the isolating liquid is extended, and the pressure sensor is protected to work stably for a long time.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: a gas phase pressure measurement isolator for tank-type storage and transportation equipment, comprising a tank body with a top opening and a top cover disposed at the top opening, the tank body and the top cover forming a sealed chamber, the sealed chamber being filled with an isolating liquid; a partition is disposed in the sealed chamber, the partition dividing the sealed chamber into an air inlet zone and a pressure measuring zone, a gap being left between the bottom of the partition and the bottom of the sealed chamber to allow communication between the air inlet zone and the pressure measuring zone, the top of the partition being higher than the liquid level of the isolating liquid; an air inlet is disposed on the tank body corresponding to the air inlet zone, the air inlet being higher than the isolating liquid; a pressure measuring port is disposed on the tank body corresponding to the pressure measuring zone, a pressure sensor being connected to the pressure measuring port; a porous adsorption block is disposed above the isolating liquid in the air inlet zone, the porous adsorption block containing an adsorbent for absorbing and neutralizing corrosive gases;

[0006] The volume of the air intake zone accounts for more than 70% of the total volume of the sealed chamber; the pressure measuring port is immersed in the isolation liquid and is set close to the liquid surface of the isolation liquid; after the gas to be measured enters the air intake zone through the air intake port, it passes through the porous adsorption block from top to bottom and acts on the isolation liquid, and the pressure is transmitted to the pressure measuring zone through the gap at the bottom of the partition.

[0007] More specifically, a baffle is provided in the air intake area, and the baffle is used to position the porous adsorption block.

[0008] More specifically, an intake valve and a check valve are provided on the air inlet, and a pressure measuring valve is provided at the pressure measuring port, the pressure measuring valve being used to connect the pressure sensor.

[0009] More specifically, a filling block is provided in the pressure measuring area near the top cover. The embedding depth of the filling block is flush with the bottom of the porous adsorption block or extends above the pressure measuring port without obstructing the pressure measuring port.

[0010] More specifically, a sealing gasket is provided between the top cover and the tank body, and the filling block is formed by the sealing gasket protruding towards the pressure measuring area.

[0011] More specifically, an observation window is provided on the tank corresponding to the air intake area, and the observation window is used to observe the state of the porous adsorption block and the isolation liquid.

[0012] More specifically, a heater is provided at the air inlet to prevent crystallization blockage.

[0013] More specifically, the adsorbent is an acidic adsorbent or an alkaline adsorbent, and a pH indicator is added to the adsorbent.

[0014] More specifically, an air vent is provided at the bottom of the sealed chamber, and an air vent valve is provided on the air vent.

[0015] More specifically, the top opening of the tank is inclined, with the top near the pressure measuring port being the lowest point and the top near the air inlet being the highest point.

[0016] The beneficial effects of this invention are: by setting a partition in the sealed chamber to divide it into an air intake zone and a pressure measurement zone, and setting a porous adsorption block in the air intake zone, the gas to be measured containing corrosive components first passes through the porous adsorption block after entering the air intake zone. The corrosive components are actively absorbed and neutralized by the adsorbent, so that the gas reaching the isolation liquid has been basically de-corrosive, reducing the probability of the isolation liquid being contaminated, extending the service life of the isolation liquid and the maintenance cycle of the pressure sensor. When negative pressure occurs inside the tank storage and transportation equipment, the porous adsorption block acts as a buffer and limiter for the isolation liquid, preventing the isolation liquid from entering the pipeline before the check valve is fully closed, thus effectively protecting the safety of the pipeline system. Attached Figure Description

[0017] Figure 1 This is a three-dimensional structural schematic diagram of the gas phase pressure measurement isolator for the tank-type storage and transportation equipment of the present invention; Figure 2 This is a cross-sectional structural schematic diagram of the gas phase pressure measurement isolator of the tank-type storage and transportation equipment of the present invention; Figure 3 This is a schematic diagram of the structure of the sealing gasket and filling block of the present invention; Figure 4 This is a schematic diagram of the porous adsorption block of the present invention; Figure 5 This is a cross-sectional structural schematic diagram (top tilted) of the gas phase pressure measurement isolator of the tank-type storage and transportation equipment of the present invention.

[0018] In the diagram: 10, Tank body; 20, Top cover; 30, Sealed chamber; 31, Air inlet area; 311, Air inlet; 312, Observation window; 32, Pressure measuring area; 321, Pressure measuring port; 40, Baffle; 41, Gap; 50, Porous adsorption block; 60, Sealing gasket; 61, Filler block; 70, Baffle; 80, Exhaust port; 100, Pressure sensor; 200, Air inlet valve; 300, Check valve; 400, Pressure measuring valve; 500, Heater; 600, Exhaust valve. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The direction of movement is also relative and is not limited to an absolute direction of movement. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, the technical features involved in the different embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] This application provides a gas phase pressure measurement isolator for tank storage and transportation equipment. The isolator is installed between the gas phase pressure detection port and the pressure sensor of the tank storage and transportation equipment, and plays the role of isolating corrosive media and transmitting gas phase pressure.

[0023] like Figure 1 and Figure 2The isolator shown includes a tank 10 with a top opening and a top cover 20 disposed at the top opening. The tank 10 and the top cover 20 cooperate to form a sealed chamber 30, which is filled with an isolating fluid. A partition 40 is provided inside the sealed chamber 30, dividing the sealed chamber 30 into an air inlet zone 31 and a pressure measuring zone 32. A gap 41 is left between the bottom of the partition 40 and the bottom of the sealed chamber 30, allowing the air inlet zone 31 and the pressure measuring zone 32 to communicate with each other. The isolating fluid can flow between the air inlet zone 31 and the pressure measuring zone 32. The gas phase pressure in the inlet zone 31 is transmitted to the pressure measuring zone 32 by free flow between the two zones. The top of the baffle 40 is higher than the liquid level of the isolation liquid, and the top is sealed and pressed tightly with the top cover 20, so that the gas phase spaces of the inlet zone 31 and the pressure measuring zone 32 are isolated from each other at the top. The gas being measured cannot flow directly from the top to the pressure measuring zone 32, but can only be transmitted through the isolation liquid, ensuring the accuracy of pressure transmission. The upper side of the tank 10 corresponding to the inlet zone 31 is provided with an air inlet 311, which is higher than the liquid level of the isolation liquid. A pressure measuring port 321 is provided on the side of the tank 10 corresponding to the pressure zone 32, and a pressure sensor 100 is connected to the pressure measuring port 321. A porous adsorption block 50 is provided above the liquid surface of the isolation liquid in the air inlet zone 31. The porous adsorption block 50 contains an adsorbent for absorbing and neutralizing corrosive gases. The gas to be tested can only be pressured by the isolation liquid after neutralization and adsorption. After the gas to be tested enters the air inlet zone 31 through the air inlet 311, it passes through the porous adsorption block 50 from top to bottom. The corrosive components in the gas to be tested are actively absorbed by the adsorbent. The gas, having passed through the porous adsorption block 50, has been largely de-corrosive. It then acts downwards on the isolation liquid and transmits pressure to the pressure measuring area 32 via the bottom gap 41 of the partition 40. Finally, the pressure sensor 100 senses and outputs a measurement signal. This application actively intercepts and neutralizes corrosive gases through the porous adsorption block 50, reducing direct contact between corrosive gases and the isolation liquid, slowing down the contamination rate of the isolation liquid, and extending the service life of the isolation liquid. This protects the pressure sensor 100 for long-term stable operation and reduces maintenance costs.

[0024] A baffle 70 is provided in the air inlet zone 31. The porous adsorption block 50 is installed and fixed on the baffle 70. The baffle 70 positions and supports the porous adsorption block 50 to prevent it from shifting when the gas flows or the surface of the isolation liquid fluctuates. This ensures that the porous adsorption block 50 is always stably positioned above the surface of the isolation liquid in the air inlet zone 31, so that the gas to be measured must pass through the porous adsorption block 50 to come into contact with the isolation liquid.

[0025] The volume of the air inlet zone 31 accounts for more than 70% of the total volume of the sealed chamber 30, ensuring that the air inlet zone 31 has sufficient space to accommodate the porous adsorption block 50 and provides ample gas phase buffer space, allowing the gas being measured to fully contact the porous adsorption block 50 and improve the absorption efficiency of corrosive gases. It also provides a buffer margin for normal fluctuations in the level of the isolation liquid, preventing excessive fluctuations in the liquid level of the air inlet zone 31 from affecting the stability of the pressure measurement. Furthermore, this proportion also ensures that the pressure measurement zone has sufficient space to ensure that the isolation liquid is always filled to the pressure measuring port, guaranteeing the accuracy of the pressure measurement. According to Pascal's law, in a closed fluid, the pressure applied to the fluid is transmitted equally to all parts of the fluid and the container walls. In the structure of this application, the gas to be measured acts on the surface of the isolation liquid in the air inlet area, and the pressure is transmitted to the pressure measuring area through the gap at the bottom of the partition. When the volume of the air inlet area (corresponding to the gas-liquid contact area) is larger than the volume of the pressure measuring area, it is equivalent to the reverse application of Pascal's principle, where the force applied on a small-area piston is output as a proportionally amplified force through a large-area piston. Increasing the effective pressure-bearing area of ​​the air inlet area means that for the same gas pressure, the total pressure acting on the isolation liquid is greater, thus making the pressure change in the pressure measuring area smoother and more stable. This effectively reduces the pressure change amplitude and response speed requirements that the pressure measuring element needs to sense. In other words, the larger the volume ratio of the air inlet area, the lower the accuracy and sensitivity requirements of the pressure sensor on the pressure measuring side. A conventional pressure sensor with lower cost and longer lifespan can be used to meet the measurement requirements.

[0026] An intake valve 200 and a check valve 300 are connected in series on the air inlet 311. A pressure measuring valve 400 is provided between the pressure measuring port 321 and the pressure sensor 100. The intake valve 200 is used to control the opening and closing of the intake channel, and the check valve 300 allows gas to flow unidirectionally from the outside into the isolator. When the tank storage and transportation equipment is under negative pressure, the check valve 300 automatically closes, cutting off the gas channel between the external pipeline and the isolator, and preventing the isolating liquid from flowing back into the external pipeline under negative pressure. At the same time, the porous adsorption block 50 in the air inlet zone 31 plays a buffering and blocking role for the isolating liquid when the check valve 300 is not fully closed, and works in conjunction with the check valve 300 to further improve the reliability of backflow prevention under negative pressure. The pressure measuring valve 400 is used to control the opening and closing of the pressure measuring channel, which facilitates the isolation operation of the pressure measuring port 321 during maintenance.

[0027] A filling block 61 is provided near the top of the pressure measuring area 32. The embedding depth of the filling block 61 is flush with the bottom end of the porous adsorption block 50, or extends above the pressure measuring port 321 without obstructing the pressure measuring port 321. The filling block 61 replaces the original gas phase space at the top of the pressure measuring area 32 with solid filling, ensuring that the pressure measuring area 32 is filled with isolation liquid without any air bubbles remaining, preventing the formation of a gas phase space above the isolation liquid in the pressure measuring area, eliminating the interference of the air bubble compression effect on pressure transmission, and ensuring the accuracy and stability of pressure transmission.

[0028] In one embodiment of the present invention, the pressure measuring port is immersed in the isolation liquid and positioned close to the surface of the isolation liquid to reduce the interference of the hydrostatic pressure of the isolation liquid column on the pressure measuring result.

[0029] like Figure 3 The top cover 20 and the tank body 10 are sealed by a sealing gasket 60. The filling block 61 is formed by the sealing gasket 60 protruding towards the pressure measuring area 32. When the top cover 20 is installed, the filling block 61 is embedded in the upper space of the pressure measuring area 32. The filling block 61 and the sealing gasket 60 are integrally formed. The fit between the filling block 61 and the tank wall of the pressure measuring area 32 provides a circumferential positioning reference for the sealing gasket 60, which facilitates accurate installation. At the same time, the top of the partition plate 40 presses the sealing gasket 60 tightly, further ensuring the isolation and sealing between the air inlet area 31 and the pressure measuring area 32 in the top gas phase space.

[0030] The side of the tank 10 corresponding to the air intake zone 31 is provided with an observation window 312. Through the observation window 312, maintenance personnel can directly observe the appearance of the porous adsorption block 50 and the color and level of the isolation fluid. They can determine whether the porous adsorption block 50 needs to be replaced or the isolation fluid needs to be replenished without disassembling the isolator, thereby reducing maintenance costs and facilitating daily management.

[0031] For gaseous media that are prone to crystallization, at low ambient temperatures, condensable components in the gas may crystallize near the inlet 311, blocking the inlet 311 channel and causing pressure measurement failure. A heater 500 is provided at the inlet 311. By activating the heater 500 to heat the inlet 311 and adjacent pipeline areas, crystal formation can be effectively prevented or existing crystals can be melted, ensuring that the inlet 311 remains unobstructed. This method is suitable for measurement conditions that are prone to crystallization or at low temperatures.

[0032] like Figure 4The adsorbent in the porous adsorption block 50 can be flexibly selected according to the properties of the corrosive gas in the measured medium. For acidic corrosive gases (such as HCl, SO2, HF, etc.), an alkaline adsorbent is selected; for alkaline corrosive gases (such as NH3, etc.), an acidic adsorbent is selected, thereby achieving targeted and efficient neutralization and absorption and improving the adsorption effect. A pH indicator is added to the adsorbent. When the adsorbent approaches saturation, the color of the pH indicator changes significantly. The usage status of the adsorbent can be intuitively judged through the observation window 312, avoiding corrosion and contamination of the isolation liquid due to untimely replacement, and realizing online status monitoring.

[0033] The bottom of the sealed chamber 30 is provided with a drain port 80, and a drain valve 600 is provided on the drain port 80. When it is necessary to replace the isolation fluid, the drain valve 600 can be opened to completely drain the isolation fluid in the sealed chamber 30, and then new isolation fluid can be injected. The operation is simple.

[0034] like Figure 5 The top opening of the tank 10 shown is inclined, with the top near the pressure measuring port 321 being the lowest point and the top near the air inlet 311 being the highest point. This inclined design allows for a larger volume on the air inlet 31 side, ensuring that the air inlet 31 has ample space to accommodate the porous adsorption block 50 and provide sufficient gas phase buffer space. At the same time, it can prevent the gas in the air inlet 31 from directly short-circuiting to the pressure measuring area 32 along the top, improving the stability of the pressure transmission path. The low point design on the pressure measuring area 32 side helps to ensure that the isolation liquid in the pressure measuring area 32 is always filled to the pressure measuring port 321, ensuring pressure measurement accuracy.

[0035] The specific workflow for this application is as follows: Normal pressure measurement conditions: The gas to be measured, containing corrosive components in the gas phase space of tank storage and transportation equipment (e.g., tank container), enters the isolator of this application through an external pipeline, passes through the inlet valve 200 and check valve 300 in sequence, and then enters the inlet zone 31 of the isolator through the inlet port 311. The gas to be measured entering the inlet zone 31 passes through the porous adsorption block 50 from top to bottom. When the corrosive gas components pass through the porous adsorption block 50, they undergo a neutralization reaction with the adsorbent and are adsorbed and fixed. After that, the gas to be measured entering the lower gas phase space of the inlet zone 31 has been basically de-corrosive. The gas to be measured continuously applies pressure to the isolation liquid in the inlet zone 31. The gas pressure is transmitted through the isolation liquid to the pressure measuring zone 32 through the bottom gap 41 of the partition 40. From the pressure measuring port 321, it acts on the pressure sensor 100 through the pressure measuring valve 400. The pressure sensor 100 converts the gas pressure into an electrical signal output to realize the measurement of the gas phase pressure.

[0036] Negative pressure protection mode: When negative pressure occurs inside the tank storage and transportation equipment (e.g., tank container), the check valve 300 of the isolator of this application automatically closes, cutting off the passage between the external pipeline and the isolator, and preventing the isolating liquid from entering the external pipeline; during the automatic closing action of the check valve 300, the porous adsorption block 50 in the air inlet zone 31 can play a buffering and limiting role for the isolating liquid because it is on the path connecting the isolating liquid to the check valve. The two work together to prevent the isolating liquid from entering the pipeline when the check valve 300 is not completely closed, effectively protecting the safety of the pipeline system.

[0037] Routine maintenance: Operators should periodically observe the color change of the porous adsorption block 50 through the observation window 312. When the pH indicator changes color beyond the usable range, it indicates that the adsorbent is approaching saturation. At this time, open the top cover 20, remove the old porous adsorption block 50, install a new porous adsorption block 50, and then replace the top cover 20. When the color of the isolation liquid is abnormal or the liquid level is insufficient, open the vent valve 600 on the vent 80 to drain the isolation liquid, and then add new isolation liquid to the specified level. In conditions prone to crystallization, start the heater 500 to prevent crystallization blockage at the air inlet 311 and ensure continuous and stable gas phase pressure measurement.

[0038] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A gas phase pressure measurement isolator for tank-type storage and transportation equipment, comprising a tank body (10) with a top opening and a top cover (20) disposed at the top opening, wherein the tank body (10) and the top cover (20) cooperate to form a sealed chamber (30), characterized in that, The sealed chamber (30) is filled with an isolation liquid; a partition (40) is provided in the sealed chamber (30), which divides the sealed chamber (30) into an air inlet zone (31) and a pressure measuring zone (32). A gap (41) is left between the bottom of the partition (40) and the bottom of the sealed chamber (30) so that the air inlet zone (31) and the pressure measuring zone (32) can communicate. The top of the partition (40) is higher than the liquid level of the isolation liquid; an air inlet (311) is provided on the tank (10) corresponding to the air inlet zone (31), which is higher than the isolation liquid; a pressure measuring port (321) is provided on the tank (10) corresponding to the pressure measuring zone (32), which is used to connect a pressure sensor (100); a porous adsorption block (50) is provided above the isolation liquid in the air inlet zone (31), which contains an adsorbent for absorbing and neutralizing corrosive gases. The volume of the air intake zone (31) accounts for more than 70% of the total volume of the sealed chamber (30); the pressure measuring port (321) is immersed in the isolation liquid and is set close to the liquid surface of the isolation liquid; after the gas to be measured enters the air intake zone (31) through the air inlet (311), it passes through the porous adsorption block (50) from top to bottom and acts on the isolation liquid, and the pressure is transmitted to the pressure measuring zone (32) through the bottom gap (41) of the partition (40).

2. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 1, characterized in that, A baffle (70) is provided in the air intake area (31), and the baffle (70) is used to position the porous adsorption block (50).

3. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 1, characterized in that, An intake valve (200) and a check valve (300) are provided on the air inlet (311), and a pressure measuring valve (400) is provided at the pressure measuring port (321). The pressure measuring valve (400) is used to connect the pressure sensor (100).

4. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 1, characterized in that, A filling block (61) is provided in the pressure measuring area (32) near the top cover (20). The embedding depth of the filling block (61) is flush with the bottom of the porous adsorption block (50) or extends above the pressure measuring port (321) without obscuring the pressure measuring port (321).

5. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 4, characterized in that, A sealing gasket (60) is provided between the top cover (20) and the tank body (10), and the filling block (61) is formed by the sealing gasket (60) protruding towards the pressure measuring area (32).

6. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 1, characterized in that, An observation window (312) is provided on the tank (10) corresponding to the air inlet area (31). The observation window (312) is used to observe the state of the porous adsorption block (50) and the isolation liquid.

7. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 1, characterized in that, A heater (500) is provided at the air inlet (311) to prevent crystallization blockage.

8. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 1, characterized in that, The adsorbent is an acidic or alkaline adsorbent, and a pH indicator is added to the adsorbent.

9. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 1, characterized in that, An air vent (80) is provided at the bottom of the sealed chamber (30), and an air vent valve (600) is provided on the air vent (80).

10. The gas phase pressure measurement isolator for tank storage and transportation equipment according to claim 1, characterized in that, The top opening of the tank (10) is inclined, with the top near the pressure measuring port (321) being the lowest point and the top near the air inlet (311) being the highest point.

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