Flowmeter

Abstract

To provide a flowmeter suitable for flow measurement of cryogenic fluid and high-temperature fluid.SOLUTION: A flowmeter 1 comprises: a flow path pipe 2 including a flow path through which fluid flows; an impeller 11 rotatably supported within the flow path pipe 2; and a sensor 3 measuring flow rate of fluid flowing in the flow path by rotation of the impeller 11. The sensor 3 includes a wiring board 24 of metal base material in a sensor case 22 installed outside the flow path pipe 2. Mounted on the wiring board 24 are: a magnetic sensor package 25 detecting magnetism of the impeller 11; a heater 26 heating the wiring board 24; and a temperature control circuit 27 detecting the temperature of the wiring board 24 and controlling power source ON / OFF of the heater 26. The wiring board 24 of the metal base material maintains uniform substrate temperature. In addition, this provides heat storage effect for maintaining a temperature at which the sensor can operate at instant stop or abnormal stop and heat radiation effect for absorbing heat around the sensor to radiate the heat.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a flowmeter suitable for measuring the flow rate of a fluid over a wide temperature range from extremely low temperatures to high temperatures. [Background technology]

[0002] In recent years, there has been a demand for measuring the flow rate of cryogenic fluids in semiconductor manufacturing processes. When measuring the flow rate of a cryogenic (e.g., -120°C) fluid (e.g., a fluorine-based refrigerant), an impeller flow meter is generally used. Because impeller flow meters use semiconductor sensors such as Hall ICs as magnetic sensors, they have poor temperature characteristics at low temperatures and become unable to detect fluid temperatures below -40°C. Therefore, a flow meter is known that employs a detection method using a pickup coil as a magnetic sensor, making it possible to measure the flow rate of cryogenic fluids (see Patent Document 1 below).

[0003] However, because the pickup coil is made of copper, it acts as an antenna and is susceptible to external magnetic field noise from all directions. Furthermore, in recent years, semiconductor manufacturing plants have been required to reduce the installation area of ​​their equipment, shortening the distance between each component within the equipment. This means that motors, solenoid valves, electromagnetic switches, inverters, power lines, and other components are located near the flowmeter, creating an environment where these components are prone to malfunction due to magnetic field noise. This means that the flowmeter must be placed as far away as possible from the equipment, making it difficult to use.

[0004] On the other hand, if a semiconductor sensor such as a Hall IC is used as in the past, the detection is directional and is not easily affected by noise from external magnetic fields, but there is a problem that the detection sensitivity of the Hall element decreases, especially when using low-temperature fluid, and detection becomes impossible. Therefore, to prevent the decrease in detection sensitivity of the Hall element, a water heater equipped with a water volume sensor having a Hall element and a heater is known (see Patent Document 2 below).

[0005] However, this water heater controls the temperature based on the ambient temperature outside the water sensor, rather than measuring the temperature near the Hall element, making accurate temperature control of the Hall element impossible. Furthermore, when used with cryogenic fluids, almost all exterior surfaces must be covered with insulating material to prevent condensation and freezing. This insulation creates a discrepancy between the ambient temperature and the sensor temperature, making accurate temperature control impossible. Furthermore, semiconductor manufacturing equipment must anticipate momentary power outages and abnormal shutdowns, and so must store heat to maintain a temperature that allows operation even when the power is turned off, even if heat is lost to the cryogenic fluid. However, no such measures are implemented. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6257833 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-294020 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a flowmeter suitable for measuring the flow rates of cryogenic fluids and high-temperature fluids. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, a flow meter according to the present invention comprises a flow tube having a flow path through which a fluid flows, an impeller rotatably supported inside the flow tube, and a sensor that measures the flow rate of the fluid flowing through the flow path by the rotation of the impeller, wherein the sensor has a wiring board made of a metal base inside a sensor case installed outside the flow tube, and the wiring board is equipped with a magnetic sensor package that detects the magnetism of the impeller, a heater that heats the wiring board, and a temperature control circuit that detects the temperature of the wiring board and controls the ON / OFF of the heater, and the magnetic sensor package is attached to the wiring board by soldering.

[0009] In the flow meter according to the present invention, the magnetic sensor package may have a structure that is a magnetic sensor package with a thermal pad in which a magnetic sensor element is mounted on a thermal pad.

[0010] In the flow meter according to the present invention, the wiring board may have a structure in which the width of the portion on which the magnetic sensor package is mounted is designed to be narrower than the width of the other portions.

[0011] Furthermore, in the flowmeter according to the present invention, the flow path pipe may be configured to include an inlet pipe having an inlet and an outlet pipe having an outlet, and a capsule having an impeller with a diameter larger than the inner diameter of the flow path may be housed in the space between the inlet pipe and the outlet pipe.

[0012] Furthermore, in the flow meter according to the present invention, a structure may be adopted in which a wave washer is inserted between the capsule and the inlet pipe, and a metal seal is inserted at the joint surface between the inlet pipe and the outlet pipe. [Effects of the Invention]

[0013] The flowmeter according to the present invention uses a semiconductor sensor with a magnetic sensor package (e.g., a Hall IC) that is less susceptible to noise from external magnetic fields. Furthermore, the temperature control circuitry mounted on a metal wiring board allows for accurate temperature control of the sensor. Therefore, the metal wiring board maintains a uniform substrate temperature while providing a heat storage effect to maintain a temperature at which the sensor can operate even during momentary or abnormal power outages. In particular, semiconductor sensors with magnetic sensor packages (e.g., Hall ICs) have a guaranteed operating temperature and are unable to detect fluid temperatures below -40°C. However, by heating the metal wiring board with a heater to maintain temperatures above -40°C, it is possible to achieve flow rate measurements suitable for cryogenic fluids. Furthermore, the metal wiring board efficiently absorbs heat near the sensor and dissipates it to the outside, enabling flow rate measurements suitable for high-temperature fluids. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing the appearance of a flow meter according to the present invention; [Figure 2] FIG. 2 is a plan view showing the appearance of the flow meter. [Figure 3] 3 is a cross-sectional view of the flowmeter taken along line AA in FIG. 2. [Figure 4] FIG. 4 is an enlarged cross-sectional view of the portion C in FIG. 3 of the flow meter. [Figure 5] 3 is a cross-sectional view of the flowmeter taken along line BB in FIG. 2. [Figure 6] 3 is a schematic diagram showing an example of a wiring substrate made of a metal base material in the flowmeter. FIG. [Figure 7] FIG. 1 is an enlarged view of the vicinity of the Hall IC in the flow meter. [Figure 8] 10 is a cross-sectional view showing a state in which a waterproof connector cable is attached to the waterproof connector of the flowmeter. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] 1 and 2, the flowmeter 1 of this embodiment is an impeller-type flowmeter that measures the flow rate of a fluid by detecting an impeller that rotates in proportion to the flow velocity, and is a sensor-integrated flowmeter in which a sensor 3 that measures the flow rate of the fluid based on the rotation speed of the impeller is attached to the outside of a flow path pipe 2 having a flow path through which the fluid flows. For example, this flowmeter 1 can be connected to the horizontal piping of a temperature-controlled chiller in semiconductor manufacturing equipment and used to measure the flow rate of a fluorine-based inert liquid. The flow rate can be measured over a wide temperature range of fluids, from the extremely low temperature of -120°C to the high temperature of +150°C.

[0017] FIG. 3 is a cross-sectional view showing the internal structure of the flow path pipe 2. As shown in the figure, the flow path pipe 2 is composed of two components: an inlet pipe 4 and an outlet pipe 5, which are made of metal, such as stainless steel (e.g., SUS316), to prevent the flow path pipe 2 from becoming magnetized due to heat during welding or processing. The inlet pipe 4 has an upstream flow path 7 that communicates with an inlet 6 opening at one end, and the outlet pipe 5 has a downstream flow path 8 that communicates with an outlet 9 opening at the other end. An impeller 11 built into a capsule 10 is installed in the space between the upstream flow path 7 and the downstream flow path 8. In an impeller-type flow meter, it is preferable to make the impeller diameter larger than the flow path diameter to reduce pressure loss. Therefore, in this embodiment, a recess 12 with a diameter larger than the inner diameter D1 of the flow paths (the upstream flow path 7 and the downstream flow path 8) is provided inside the outlet pipe 5, and the capsule 10 with the built-in impeller 11 is accommodated in the recess 12.

[0018] The capsule 10 is made of a thermoplastic resin (e.g., PPS) that has excellent heat resistance. Ceramic (e.g., alumina) bearings 13 and 14 are arranged facing each other in the center of the capsule 10, and a straightening plate (e.g., PPS) 15 is integrally molded radially around the bearing 13 on the inlet pipe 4 side. The impeller 11 has four blades 17, 17, ... made of a thermoplastic resin (e.g., PPS) that are radially and spirally arranged around the outer periphery of a ceramic (e.g., alumina) rotating shaft 16. Of the four blades 17 (17A, 17B, 17C, 17D), two blades 17 (17B and 17D) that are 180 degrees apart have magnets 18 embedded therein that are made of samarium cobalt or the like that have excellent heat resistance and corrosion resistance. The impeller 11 is designed so that its outer diameter D2 is larger than the inner diameter D1 of the flow paths (upstream flow path 7 and downstream flow path 8), and is supported rotatably around the axis of a rotating shaft 16 supported by bearings 13 and 14.

[0019] In the flow pipe 2, the fluid that flows into the capsule 10 from the inlet 6 through the upstream flow path 7 is turned into a vortex by the straightening vane 15 and the spiral blades 17, and flows out of the outlet 9 through the downstream flow path 8. In this embodiment, an axial flow system is used in which the fluid is directed perpendicularly to the rotational plane of the impeller 11. This means that there are no restrictions on the mounting orientation (vertical or horizontal) of the flowmeter 1 to the piping, and axial stress is small, resulting in fewer breakdowns and a longer lifespan. Furthermore, since it is only necessary to fit the capsule 10, which is a pre-assembled unit containing the impeller 11, bearings 13 and 14, and straightening vane 15, into the recess 12, the assembly of parts is simplified and maintenance can be easily performed.

[0020] The flowmeter 1 of this embodiment employs a unitized capsule housing structure that is less likely to misalign the centers of the bearings 13, 14 supporting the impeller 11 and reduces pressure loss. This requires a seal at the interface between the inlet pipe 4 and the outlet pipe 5. While rubber packing such as an O-ring is typically used for the seal, this rubber packing hardens and becomes incapable of sealing at temperatures below -50°C. Therefore, a metal seal is employed in this embodiment. Specifically, a wave washer 19 made of metal (e.g., SUS304) is inserted between the capsule 10 and the inlet pipe 4 to prevent the capsule 10 from rattling. Furthermore, a metal seal 20 made of metal (e.g., SUS304) is inserted in a portion of the interface between the inlet pipe 4 and the outlet pipe 5. The interface between the inlet pipe 4 and the outlet pipe 5 is sealed by fastening a plurality of hexagon socket head bolts 21, 21, ... to the inlet pipe 4 from the outside.

[0021] Because typical metal seals have a lower manufacturing yield than rubber gaskets, this embodiment significantly improves yield by shaping the gasket to limit the contact area. When tightened with a hexagon socket head bolt, the product is pressed in the direction of the arrow, as shown in Figure 4, crushing the gasket. However, a typical gasket is often pressed against the entire surface, dispersing the load per area and resulting in poor sealing performance. Therefore, the metal seal 20 of this embodiment is shaped to limit the contact area by reducing the contact area a with the inlet pipe 4 and the contact area b with the outlet pipe 5. This limits the contact area, applying force only to the circled areas in the figure, enabling high sealing performance with a low tightening force.

[0022] Furthermore, because general metal seals are tightened by rotating the entire seal, the packing slides in the direction of rotation during rotation, which can cause frictional heat and adhesion on the surface, leading to problems with the surface becoming sore and impairing sealing performance. Therefore, in this embodiment, by adopting a fastening structure using hexagon socket bolts 21, force is applied only in the vertical direction, preventing frictional heat and adhesion on the surface, and preventing surface soreness. This makes it possible to achieve high sealing performance, eliminates the need for additional components to solve these problems, and enables inexpensive metal seals.

[0023] Pipe threads, such as conventional Rc threads, are sealed using sealing tape or rubber or resin sealants. However, these seals have the problem of greater thermal contraction than metals at low temperatures when connected to metal fittings, such as stainless steel, resulting in increased susceptibility to liquid leakage. Therefore, in this embodiment, the inlet pipe 4 and the outlet pipe 5 have a tube-like structure rather than pipe threads. This allows the attachment of double-ferrule Swagelok tube fittings (manufactured by Swagelok, product name) or VCR fittings (manufactured by Swagelok, product name) by welding the tube ends to the flow path pipe 2. This allows the flow path pipe 2 and the fittings to be made of the same material and have the same thermal expansion coefficient even at low temperatures, maintaining high airtightness without the risk of gaps or liquid leakage, even when using low-temperature fluids.

[0024] 5 is a cross-sectional view showing the internal structure of the sensor 3. As shown in the figure, the sensor 3 is housed in a sensor case 22 made of a thermoplastic resin (e.g., PPS) with excellent heat resistance. The sensor case 22 is installed outside the flow path pipe 2 by fastening it to the flow path pipe 2 with tapping screws 23. Inside the sensor case 22, a wiring board 24 made of a metal base material with high thermal conductivity is built in.

[0025] The metal substrate wiring board 24 includes the metal base board 24-1, metal core board 24-2, and metal post board 24-3 shown in FIG. 6. The metal base board 24-1 is formed by laminating an insulating layer on the surface of a metal plate (aluminum plate or copper plate) that serves as the base (substrate) and forming an outer layer circuit on top of that. The metal core board 24-2 is formed by laminating insulating layers on the front and back surfaces of a metal plate (aluminum plate or copper plate) that serves as the core (substrate) and forming an outer layer circuit on top of that and providing through holes. The metal post board 24-3 is formed by laminating an insulating layer on the surface of a metal plate (aluminum plate or copper plate) that serves as the base (substrate) and forming an outer layer circuit on top of that, exposing the metal plate.

[0026] A non-contact magnetic sensor package 25 for detecting the magnetic field of the impeller 11 is mounted on the metal wiring board 24, facing the impeller 11 inside the flow tube 2. The magnetic sensor package 25 in this embodiment is a Hall IC incorporating a Hall element that converts magnetic field into voltage using the Hall effect. The magnetic sensor package (Hall IC) 25 is an electronic component package consisting of a chip circuit including a Hall element, a power supply circuit, an operational amplifier, a Schmitt trigger, and a transistor. Its function is to detect the rotation speed using magnetic fields. When fluid passes through the flow tube 2, the magnet 18 rotates in conjunction with the rotation of the impeller 11. Each time the magnet 18 passes, a magnetic field is output to the outside of the flow tube 2. When the magnetic sensor element (Hall element) of the magnetic sensor package (Hall IC) 25 detects the magnetic field, a potential difference is generated. This potential difference is amplified by the operational amplifier. When the Schmitt trigger detects a value above an upper limit or below a lower limit, a transistor outputs an ON / OFF (Lo / Hi) digital signal.

[0027] Mounted on the metal wiring board 24 are a heater 26 for heating the wiring board 24, a temperature control circuit 27 for controlling the ON / OFF of the heater 26, and a temperature sensor 28 for detecting the temperature of the wiring board 24. The heater 26 is made of an electrical resistor, and when powered on and a current flows, it generates heat to heat the wiring board 24, preventing a drop in temperature of the magnetic sensor element (Hall element) of the magnetic sensor package (Hall IC) 25. The temperature sensor 28 detects the temperature of the wiring board 24 using a thermistor or the like. The temperature control circuit 27 controls the temperature of the wiring board 24 by turning on the power to the heater 26 when it detects that the temperature of the wiring board 24 is below a set temperature (lower limit) or by turning off the power to the heater 26 when it detects that the temperature is above the set temperature (upper limit). Note that although the temperature control circuit 27 and the temperature sensor 28 are separate components, a single-chip electronic component such as a temperature control circuit with a built-in temperature sensor may also be used.

[0028] In this embodiment, the magnetic sensor package (Hall IC) 25 is attached to a metal wiring board 24 by soldering. For example, as shown in FIG. 7A, a structure can be adopted in which terminals 25b connected to the magnetic sensor element (Hall element) 25a are mounted to electrodes 24a of the wiring board 24 by solder s. In this way, metal-to-metal fastening enables stable, high-precision positioning of the magnetic sensor element (Hall element) 25a over a long period of time. Furthermore, even if the device is repeatedly used in a wide temperature range from -120°C to +150°C, peeling of the electronic components due to heat cycles can be prevented because the metals have similar thermal expansion coefficients. Furthermore, the temperature of the wiring board 24 is easily transferred directly to the magnetic sensor element (Hall element) 25a via the solder s and terminals 25b, which are metals with good thermal conductivity, thereby achieving high-precision temperature control.

[0029] 7(B), a magnetic sensor package with a thermal pad may be used as another example of the magnetic sensor package (Hall IC) 25. That is, a magnetic sensor package (Hall IC) 25 having a magnetic sensor element (Hall element) 25a mounted on the surface of a thermal pad 29 made of a copper plate may be used, and the thermal pad 29 on the back side may be attached to an electrode 24a of a wiring board 24 with solder s. This provides copper, which has good thermal conductivity, between the wiring board 24 and the magnetic sensor element (Hall element) 25a, making it possible to maintain the wiring board 24 and the magnetic sensor element (Hall element) 25a at approximately the same temperature, thereby achieving highly accurate temperature control due to extremely high thermal conductivity.

[0030] As shown in FIG. 5 , the metal wiring board 24 is inserted into the sensor case 22 via a resin board holder 30. A rubber gasket 31 prevents moisture from entering from the outside, and a waterproof connector 32 for an M12 connector prevents the board from coming loose and provides waterproof protection. Internal cables 33, such as power conductors and signal conductors, are arranged inside the sensor case 22. A filler material (e.g., heat-resistant epoxy resin) 34 is adhesively fixed to cover the periphery of these internal cables 33. This prevents air convection within the interior space of the sensor case 22, preventing heat transfer from the flow path pipe 2 to the wiring board 24 even when a high-temperature fluid flows through the flow path. Conversely, condensation on the wiring board 24 can be suppressed even when a low-temperature fluid flows through the flow path. Even if the flow path pipe 2 condenses or freezes, the internal conductors will not rust, preventing poor contact of the internal cable 33. Furthermore, even if the adhesive between the filler material 34 and the sensor case 22 peels off due to thermal fluctuations, the board holder 30 stably fixes the wiring board 24 and prevents it from coming loose.

[0031] As described above, in this embodiment, the magnetic sensor package (Hall IC) 25, heater 26, temperature control circuit 27, and temperature sensor 28 are mounted on a single metal wiring board 24 and inserted into the sensor case 22 for independent temperature control outside the flow path pipe 2. This enables accurate temperature control around the magnetic sensor package (Hall IC) 25. Therefore, the metal wiring board 24 maintains a uniform substrate temperature while providing a heat storage effect for maintaining a temperature at which the sensor 3 can operate even during momentary power outages or abnormal shutdowns. In particular, the semiconductor sensor of the magnetic sensor package (Hall IC) 25 has a guaranteed operating temperature and is unable to detect fluid temperatures below -40°C. However, by heating the metal wiring board 24 with the heater 26 to maintain temperatures above -40°C, flow rate measurement suitable for cryogenic fluids can be achieved.

[0032] Furthermore, the magnetic sensor package (Hall IC) 25 is positioned close to the magnet 18 so that it can detect the magnetism of the magnet as strongly as possible, and a Hall element with as low sensitivity as possible is used to reduce the influence of external magnetic fields. Therefore, since the sensor 3 is positioned near the flow path of the flow path pipe 2, there is a problem that it is easily affected directly by the heat of the fluid. Therefore, as shown in FIG. 2, the wiring board 24 of this embodiment is designed so that the board width W1 of the portion where the magnetic sensor package (Hall IC) 25 closest to the flow path is mounted is extremely narrow compared to the board width W2 of the other portion where the heater 26, temperature control circuit 27, and temperature sensor 28 are mounted. This has the advantage of reducing the heat input that the wiring board 24 receives from the flow path side.

[0033] Furthermore, while low-temperature fluids can be heated by the heater 26, heat dissipation is advantageous in high-temperature fluids, allowing for use with even higher-temperature fluids. In this embodiment, the magnetic sensor package (Hall IC) 25 is soldered onto the metal wiring board 24, so that heat received by the magnetic sensor element (Hall element) 25a is efficiently absorbed by the metal wiring board 24, which has high thermal conductivity. Furthermore, as shown in FIG. 8, the heat absorbed by the wiring board 24 is efficiently transferred from the internal cable 33 to the external cable 35 via the pin 32a of the waterproof connector 32, and then dissipated into the outside air from the waterproof connector cable 36, which is exposed to the outside air. This heat dissipation effect allows the heat received by the magnetic sensor element (Hall element) 25a from the flow path to be efficiently dissipated to the outside of the flowmeter, enabling flow rate measurements suitable for high-temperature fluids.

[0034] In the above-described embodiment, a Hall element is used as the magnetic sensor element 25a of the magnetic sensor package 25 that detects the magnetism of the impeller 11. However, the type of magnetic sensor element 25a is not limited to this. For example, as a Hall sensor utilizing the Hall effect, a Hall element that directly outputs a Hall voltage or a linear Hall IC that amplifies the Hall voltage and outputs it linearly can be used. Furthermore, as an MR sensor utilizing the magnetoresistance (MR) effect, a GMR sensor element using the giant magnetoresistance (GMR) effect or a TMR sensor element using tunneling magnetoresistance (TMR) can also be used. Furthermore, although PPS is used as the material for the sensor case 22, foamed PPS, which has excellent heat insulating properties, may also be used. [Industrial Applicability]

[0035] In the above embodiment, an example of the use of the flowmeter of the present invention has been given in which it is used to measure the flow rate of a fluorine-based inert liquid in a temperature-controlled chiller of semiconductor manufacturing equipment, but it can also be used to measure the flow rate of hydraulic equipment, etc. [Explanation of symbols]

[0036] 1:Flow meter 2: Flow path pipe 3: Sensor 4:Inflow pipe 5:Outflow pipe 6:Inlet 7:Upstream route 8: Downstream path 9: Outlet 10: Capsule 11: Impeller 12: Recess 13: Bearing 14: Bearing 15: Rectifier plate 16: Rotation axis 17: Feather 18: Magnet 19: Wave washer 20: Metal seal 21: Hexagon socket head bolt 22: Sensor case 23:Tapping screw 24: Wiring board 24a: Electrode 25: Magnetic sensor package (Hall IC) 25a: Magnetic sensor element (Hall element) 25b: Terminal 26: Heater 27: Temperature control circuit 28: Temperature sensor 29: Thermal pad 30: Board holder 31: Rubber packing 32: Waterproof connector 32a: pin 33: Internal cable 34: Filling material 35: External cable 36: Waterproof connector cable

Claims

1. a flow path pipe having a flow path through which a fluid flows; an impeller rotatably supported inside the flow tube; a sensor for measuring the flow rate of a fluid flowing through the flow path by rotation of the impeller; the sensor has a wiring board made of a metal base material in a sensor case installed outside the flow path pipe, a magnetic sensor package for detecting the magnetism of the impeller, a heater for heating the wiring board, and a temperature control circuit for detecting the temperature of the wiring board and controlling ON / OFF of the heater; The flow meter is characterized in that the magnetic sensor package is attached to the wiring board by soldering.

2. 2. The flow meter according to claim 1, wherein the magnetic sensor package is a magnetic sensor package with a thermal pad in which a magnetic sensor element is mounted on a thermal pad.

3. 3. The flow meter according to claim 1, wherein the wiring board is designed so that the width of the portion where the magnetic sensor package is mounted is narrower than the width of the other portion.

4. 4. The flow meter according to claim 1, wherein the flow path pipe is composed of an inlet pipe having an inlet and an outlet pipe having an outlet, and a capsule having an impeller with a diameter larger than an inner diameter of the flow path is accommodated in a space between the inlet pipe and the outlet pipe.

5. 5. The flow meter according to claim 4, wherein a wave washer is inserted between the capsule and the inlet pipe, and a metal seal is inserted at a joint surface between the inlet pipe and the outlet pipe.

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