JP7469131B2 - Flow path switching mechanism and positioner - Google Patents

Description

The present invention relates to a flow path switching mechanism that switches the air outflow path between a state in which the valve body is seated on the valve seat and a state in which the valve body is separated from the valve seat, and a positioner equipped with this flow path switching mechanism.

Conventionally, positioners have been widely used to control the opening and closing of air-operated control valves. As described in Patent Document 1, for example, this type of positioner includes a flow path switching mechanism that switches the operation mode between "auto" and "manual." When the operation mode is "auto," the opening of the control valve is automatically controlled according to a predetermined set value. When the operation mode is "manual," the output pressure of the positioner can be changed by changing the pressure of the control air supplied to the positioner with a manual pressure reducing valve, and the opening of the control valve can be manually operated.

This flow path switching mechanism is used when installing and adjusting the control valve, and can be operated manually without requiring a power source.
The flow path switching mechanism disclosed in Patent Document 1 switches to an "auto" mode by tightening a screw member screwed into a housing of a positioner, and switches to a "manual" mode by loosening the screw member.

JP 2010-185540 A

In conventional flow path switching mechanisms, the only way to check the current mode of the positioner in a de-energized state is to visually check whether the screw member is screwed in or loosened. This means that there is a risk that after installation and adjustment work is completed, the worker will forget to operate the flow path switching mechanism so that the positioner is in "auto" mode. If the worker forgets to switch the flow path switching mechanism so that the positioner is in auto mode, the positioner will not be able to control the opening after operation begins. Because the positioner has a complex structure, it often takes a long time to determine the reason why opening control is not possible.

The most useful situation for a flow path switching mechanism that switches between "auto" and "manual" is when checking the operation of a control valve when power is not being supplied to the positioner. For this reason, it is not possible to adopt solutions that rely on electricity, such as detecting the switching state with a sensor or recognizing the state by an electrical display.

The object of the present invention is to provide a flow path switching mechanism and positioner that allows easy identification of the "auto" and "manual" states.

In order to achieve this object, the flow path switching mechanism of the present invention includes a valve body that is accommodated in a valve body accommodating section formed in the thickness of a housing and can be moved forward and backward from the outside of the housing, and switches the outflow path of the supply air supplied from the outside of the housing between a first state in which the valve body is seated on a valve seat provided in the valve body accommodating section and a second state in which the valve body is separated from the valve seat. The valve body has an inlet that allows the supply air to flow into the valve body, an outlet that allows the supply air that has flowed into the valve body to flow out of the valve body, and an internal communication passage provided in the valve body that communicates the inlet and the outlet. An external communication passage that communicates the valve body accommodating section with the outside of the housing is formed in the thick part of the housing, and the external communication passage is closed by the outer circumferential surface of the valve body when the valve body is in the first state, but is open when the valve body is in the second state, allowing a portion of the supply air that has flowed into the valve body to pass through. The flow path switching mechanism includes a sounding body that is connected to the outside side of the housing of the external communication passage and generates sound by the air passing through the external communication passage.

In the flow path switching mechanism of the present invention, the supply air that has passed through the valve seat is guided to a passage that communicates with the nozzle passage and the back pressure passage, and a first and second O-rings are attached between the outer circumferential surface of the tip of the valve body and the inner wall surface of the valve body housing, and the outlet comprises a first outlet that opens into a passage that communicates with the nozzle passage and the back pressure passage, and a second outlet that opens into a space partitioned by the first and second O-rings in the valve body housing, and a fixed throttle is provided in the first outlet, and when the valve body is in a first state, the supply air that has flowed in from the inlet passes through the internal communication passage and only the fixed throttle to reach the passage that communicates with the nozzle passage and the back pressure passage, and when the valve body is in a second state, the supply air that has flowed in from the inlet passes through the internal communication passage and passes through the fixed throttle and the second outlet to reach the passage that communicates with the nozzle passage and the back pressure passage.

The positioner according to the present invention is a positioner comprising an electro-pneumatic converter that converts an electrical signal into a pneumatic signal using air supplied from the outside, a pilot relay that amplifies the pneumatic signal from the electro-pneumatic converter, and a housing that houses at least the electro-pneumatic converter, the housing having a passage that guides the pneumatic signal to the pilot relay, and a valve body housing portion formed in the passage houses the valve body of the flow path switching mechanism described in claim 1 or claim 2 so that it can be operated to advance and retreat from outside the housing.

According to the present invention, when the valve body of the flow path switching mechanism is in the first state, no sound is generated from the sound generating body, and when the valve body is in the second state, the sound generating body generates sound. Therefore, by configuring the positioner to be in "auto" mode when the valve body is in the first state, and configuring the positioner to be in "manual" mode when the valve body is in the second state, it is possible to provide a flow path switching mechanism and positioner that can easily distinguish between the "auto" and "manual" states.

FIG. 1 is a block diagram showing a positioner equipped with a flow path switching mechanism according to the present invention. FIG. 2 is a cross-sectional view showing the configuration of a positioner using the flow path switching mechanism according to the first embodiment. FIG. 3 is a cross-sectional view of the flow path switching mechanism in the auto mode. FIG. 4 is an enlarged cross-sectional view of a portion of FIG. FIG. 5 is a cross-sectional view of the flow path switching mechanism in the manual mode. FIG. 6 is an enlarged cross-sectional view of a portion of FIG. FIG. 7 is a cross-sectional view of a flow path switching mechanism provided in the pilot relay. FIG. 8 is a cross-sectional view of a flow path switching mechanism provided in the pilot relay. FIG. 9 is a cross-sectional view of the flow path switching mechanism according to the second embodiment. FIG. 10 is a cross-sectional view of the flow path switching mechanism according to the second embodiment.

(First embodiment)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a flow path switching mechanism and a positioner according to the present invention will be described in detail below with reference to FIGS.
The positioner 1 shown in Fig. 1 is for controlling the opening and closing of an air-operated control valve 2. The positioner 1 includes an electric/air converter (electro-pneumatic converter) 4 that converts an input signal I0 sent as an electric signal from a higher-level controller 3 into an air pressure signal (nozzle back pressure) PN, a pilot relay 6 that amplifies the nozzle back pressure PN and outputs it to a drive device 5 of the control valve 2 as an air pressure signal P0, and a flow path switching mechanism 7 that switches the operation mode of the control valve 2 between auto and manual. In Fig. 1, the reference symbol PS denotes an air supply source, and 8 denotes a pressure reducing valve. Air supplied from the air supply source PS is supplied to the pilot relay 6 through the pressure reducing valve 8.

The positioner 1 can be configured as shown in FIG. 2, for example. In FIG. 2, the positioner 1 has a housing 11 made of a pressure-resistant explosion-proof structure. Inside the housing 11, an electro-pneumatic converter 4 that converts an electric input signal I0 into an air pressure signal (nozzle back pressure PN), a feedback mechanism 12 that feeds back the actual operating amount of the control valve 2, a control unit 13, etc. are housed, and outside, a pilot relay 6 that amplifies the air pressure signal from the electro-pneumatic converter 4 and outputs it as an output air pressure P0 to the drive device 5 of the control valve 2 is arranged, and further, inside the wall thickness, a flow path switching mechanism 7 that switches the operation mode of the control valve 2 between two modes (auto mode, manual mode) described later, etc. are incorporated. The lever 12a of the feedback mechanism 12 protrudes freely swingably outside the housing 11 and is connected to the valve shaft 14 of the control valve 2.

(Explanation of electropneumatic converter)
The electro-pneumatic converter 4 is composed of a magnet unit 17 including a yoke 15 and an exciting coil 16, and a nozzle flapper mechanism 20 including a nozzle 18, a flapper 19, and the like.
The nozzle 18 is connected to an air supply source PS via a flow path switching mechanism 7 and an air supply passage 21, which will be described later, and is supplied with a supply air pressure Psup (normally 1.4 kgf/ ^cm2 ) when the flow path switching mechanism 7 is switched to the auto mode. A pilot relay 6, a pressure reducing valve 8, a supply air pressure gauge 22, etc. are provided in the air supply passage 21.

When the excitation coil 16 is excited by an electrical input signal I0 (e.g., 4 to 20 mA) and the flapper 19 is caused to swing about its fulcrum 23, the gap (nozzle gap) between the nozzle 18 and the flapper 19 changes, changing the back pressure PN of the nozzle 18. This nozzle back pressure PN is amplified by the pilot relay 6 and output to the drive unit 5 as the output air pressure PO, which drives the drive unit 5 to displace the valve shaft 14 in the vertical direction, thereby automatically adjusting the valve opening of the control valve 2. The movement of the valve shaft 14 is received by the feedback mechanism 12 and fed back to the electro-pneumatic converter 4, stabilizing the movement of the flapper 19.

(Pilot relay explanation)
The pilot relay 6 is composed of a case 40 whose interior is partitioned by two partition walls 31, 32 and two diaphragms 33, 34 into five chambers, namely, an air supply chamber 35, an output chamber 36, an atmosphere release chamber 37, a bias chamber 38 and a back pressure chamber 39, a poppet valve 41, a piston valve 42, etc. The air supply chamber 35 is connected to an air supply source PS via an air supply passage 21, and is also connected to a nozzle 18 via a flow path switching mechanism 7.

The output chamber 36 communicates with the air supply chamber 35 through communication holes 43 provided in the partitions 31 and 32, and can communicate with the atmosphere open chamber 37 through an exhaust passage 44 provided in the piston valve 42, and is also connected to the drive unit 5 through a pipe 45. The atmosphere open chamber 37 communicates with the outside of the case 40 through a vent hole 46. The supply air pressure P SUP is supplied to the bias chamber 38 through a passage 47, and the nozzle back pressure PN is supplied to the back pressure chamber 39 through a back pressure passage 48.
The back pressure passage 48 is connected to a nozzle passage 49 extending from the nozzle 18 and a control pressure passage 50 extending from the flow path switching mechanism 7 .

The poppet valve 41 passes through the communication hole 43 so as to be freely movable back and forth, and controls the opening and closing of the communication hole 43 and the exhaust passage 44 of the piston valve 42. It is biased in the closing direction by a spring (not shown), i.e., in the direction of closing the communication hole 43 and the exhaust passage 44. The piston valve 42 is held by two diaphragms 33, 34, and its lower end is slidably inserted into the through hole 32a provided in the partition wall 32 via an O-ring (not shown).

When such a pilot relay 6 is used as a positive action type in which the output increases with an increase in input, when the nozzle back pressure PN flowing into the back pressure chamber 39 through the back pressure passage 48 increases, the diaphragms 33, 34 are displaced downward. This causes the piston valve 42 to move down, which in turn causes the poppet valve 41 to move down. As a result, the lower valve body 41a of the poppet valve 41 moves away from the partitions 31, 32, opening the communication hole 43 and connecting the air supply chamber 35 to the output chamber 36. Therefore, the supply air pressure PSUP supplied to the air supply chamber 35 from the air supply passage 21 flows into the output chamber 36 through the communication hole 43, increasing the pressure in the output chamber 36. This pressure in the output chamber 36 is then supplied to the drive unit 5 through the piping 45 as the output air pressure PO.

On the other hand, when the nozzle back pressure PN decreases from this state, the piston valve 42 rises and returns due to the output air pressure PO and the pressure in the bias chamber 38 (bias pressure), and the poppet valve 41 rises and returns due to the repulsive force of a spring (not shown). At this time, the upper valve body 41b of the poppet valve 41 separates from the bottom surface of the piston valve 42 to open the exhaust passage 44, connecting the output chamber 36 and the exhaust passage 44. As a result, the pressure in the output chamber 36 is exhausted to the outside of the case 40 via the exhaust passage 44, the atmospheric open chamber 37, and the vent hole 46.

(Explanation of flow path switching mechanism)
3, the flow path switching mechanism 7 includes a valve body 56 that is screwed into a valve body accommodating portion 51 formed within the wall thickness of the housing 11 (casing) via first to fourth O-rings 52 to 55. The valve body accommodating portion 51 is formed in a passage that introduces an air pressure signal to the pilot relay 6.
The valve element 56 is accommodated in the valve element accommodating portion 51 so as to be operable to advance and retreat from outside the housing 11, and is used in either a first state in which a first O-ring 52 provided at the tip is in contact with a valve seat 57 formed by the bottom surface of the valve element accommodating portion 51, or a second state in which the first O-ring 52 is spaced apart from the valve seat 57 as shown in Fig. 5. The outflow path of the supply air supplied from outside the housing 11 is switched between the first state and the second state, as will be described in detail later.

The valve body 56 has an inlet 61 for air supplied from the outside formed in its center, a first outlet 62 and a second outlet 63, 64 for air supplied from the outside formed in its tip, and an internal communication passage 65 that connects the inlet 61 to the first outlet 62 and the second outlet 63, 64 is formed in its center. In this example, the inlet 61 is formed in the center of the valve body 56 as an opening that connects to the air supply passage 21, and the first outlet 62 is formed in the tip of the valve body 56 as an opening that connects to the control pressure passage 50 in the housing 11 that connects to the back pressure passage 48 and the nozzle passage 49. In addition, the first and second outlets 63, 64 are formed on the outer circumferential surface of the tip of the valve body 56 as openings that face the space S partitioned by the first O-ring 52 and the second O-ring 53 in the valve body accommodating portion 51.

A fixed throttle 66 is provided at the tip of the valve body 56 on the side of the outflow port 62 in the interior communication passage 65. A cylindrical filter 67 is detachably provided at the center of the valve body 56 so as to cover the body of the valve body 56 where the inflow port 61 is formed, and absorbs and removes foreign matter such as dust and oil contained in the air supplied to the inflow port 61. The back pressure passage 48 and nozzle passage 49 which communicate with the control pressure passage 50 in the housing 11 are designed so that the nozzle passage 49 has a passage width which is significantly narrower than that of the back pressure passage 48.
A male thread 72 is formed at the rear end of the valve body 56, which screws into a female thread 71 (described later) of the valve body accommodating portion 51. A diametric groove 73 is formed at the rear end surface of the valve body 56, into which a screwdriver or the like is inserted when rotating the valve body 56.

The valve body housing portion 51 has first to fourth holes 51a to 51d by being a variable diameter hole that becomes smaller toward the back. One end of a control pressure passage 50, the other end of which is connected to the back pressure passage 48 and the nozzle passage 49, opens into the bottom surface of the valve body housing portion 51. The first hole 51a at the innermost part is connected to the bottom surface of the valve body housing portion 51. A first O-ring 52 is in contact with this first hole 51a.

The second O-ring 53 contacts the second hole 51b, which is the second from the back, and one end of the external communication passage 74 is open to it. One end of the external communication passage 74 is formed near the boundary between the second hole 51b and the third hole 51c. The other end of the external communication passage 74 opens to the outer surface of the housing 11 and is connected to the sounding body 81, which will be described later. In other words, the external communication passage 74 communicates between the valve body accommodating section 51 and the outside of the housing (outside the casing).

The third hole 51c, which is the third from the back, is connected to the tip 21a of the air supply passage 21 extending from the air supply chamber 35, and a female screw 71 is formed in front of the tip 21a.
The third and fourth O-rings 54 and 55 are in contact with the fourth hole 51d located at the frontmost side.

The sound generator 81 generates sound using the air reed 82 as a sound source, and is attached to the outer surface of the housing 11 so that air is blown from the external communication passage 74 onto the air reed 82. Sound is generated by air being blown onto the air reed 82 from the external communication passage 74.

(Description of positioner operation)
〔auto mode〕
In the positioner 1 equipped with this flow path switching mechanism 7, when automatically controlling the regulator valve 2, the flow path switching mechanism 7 is switched to the auto mode. Fig. 3 shows a state in which the flow path switching mechanism 7 is switched to the auto mode. In this case, the valve body 56 is held in a first state in which the first O-ring 52 of the valve body accommodating portion 51 is seated on the valve seat 57.
When supply air is supplied to the positioner 1, the supply air flows from the air supply chamber 35 through the tip 21a of the air supply passage 21 and into the valve body accommodating portion 51. As shown by the two-dot chain line in Figure 3, the supply air passes through a filter 67, enters the inlet 61 of the valve body 56, passes through the internal communication passage 65 and the fixed throttle 66, reaches the control pressure passage 50, and is sent to the back pressure passage 48 and the nozzle passage 49.

In other words, in the auto mode, the supply air from the air supply source PS passes only through the fixed throttle 66 and is sent to the control pressure passage 50, and the nozzle back pressure PN created by the small flow rate of supply air sent to this control pressure passage 50 is supplied to the back pressure chamber 39 of the pilot relay 6 through the back pressure passage 48, and this nozzle back pressure PN is amplified by the pilot relay 6 and output as the air pressure signal PO, thereby automatically controlling the adjustment valve 2.

Some of the supply air that flows into the valve body housing 51 may leak through a small gap between the valve body 56 and the second hole 51b of the valve body housing 51 and flow out into the external communication passage 74. This leaked air passes through the external communication passage 74 and flows into the sounding body 81. At this time, the flow rate of the supply air passing through the external communication passage 74 is a flow rate that is only a slight leakage, so even if this supply air flows into the sounding body 81, no sound will be generated from the sounding body 81. In other words, when the valve body 56 is in the first state, the external communication passage 74 is essentially closed by the outer circumferential surface of the valve body 56.

[Manual mode]
On the other hand, when the control valve 2 is switched to the manual mode for maintenance, zero adjustment, or the like, the valve element 56 is rotated to move (retract) rightward in Fig. 3 to set up a second state in which the first O-ring 52 is separated from the valve seat 57 as shown in Fig. 5. In this case, the supply air that flows in from the inlet 61 passes through the internal communication passage 65, the fixed throttle 66, and the first and second outlets 62-64, as shown by the two-dot chain arrow in Fig. 5, to reach the control pressure passage 50, and is sent to the back pressure passage 48 and the nozzle passage 49.

In other words, in manual mode, the supply air from the air supply source PS passes through not only the fixed throttle 66 but also the second outlet ports 63, 64, and passes through the bypass passage 83 consisting of the gap between the tip of the valve body 56 and the inner surface of the valve body accommodating portion 51 (the first and second holes 51a, 51b) to the control pressure passage 50, increasing the flow rate of the supply air sent to the control pressure passage 50. In this example, the cross-sectional area of the bypass passage 83 is about 10 times the cross-sectional area of the fixed throttle 66. This makes it possible to manually adjust the opening of the control valve 2 by operating the pressure reducing valve 8 to change the supply air pressure P SUP.

A portion of the supply air that passes through the second outlets 53, 54 and flows into the second hole 51b enters the external communication passage 74 as shown by the two-dot chain arrow in FIG. 6, and flows through the external communication passage 74 into the sounding body 81. That is, when the valve body 56 is in the second state, the external communication passage 74 is opened, allowing a portion of the supply air that has flowed into the valve body 56 to pass through. At this time, the flow rate of the supply air flowing through the external communication passage 74 is greater than the flow rate in the auto mode. Therefore, at this time, a large amount of air is blown into the sounding body 81, causing the sounding body 81 to generate sound.

Thus, according to this embodiment, when the valve body 56 of the flow path switching mechanism 7 is in the first state and the positioner 1 is in the auto mode, no sound is generated from the sound generator 81, and when the valve body 56 is in the second state and the positioner 1 is in the manual mode, sound is generated from the sound generator 81. Therefore, it is possible to provide a flow path switching mechanism and a positioner that can easily distinguish between the "auto" and "manual" states.

(Modification of the first embodiment)
In the above-described embodiment, the flow path switching mechanism 7 is provided in the housing 11 that houses the electro-pneumatic converter 4 and the like, but as shown in Figures 7 and 8, it may be provided in the case 40 of the pilot relay 6. In Figures 7 and 8, the same reference numerals are used for members that are the same as or equivalent to those described in Figures 1 to 6, and detailed descriptions will be omitted as appropriate. Figure 7 shows the auto mode, and Figure 8 shows the manual mode.

7 and 8, a valve body accommodating portion 51 is formed within the wall thickness of the case 40 of the pilot relay 6. A valve body 56 is accommodated in this valve body accommodating portion 51. This valve body 56 is configured so as to be manually rotated from the outside of the case 40.
When the flow path switching mechanism 7 is provided in the case 40 of the pilot relay 6 in this manner, the external communication passage 74 is formed so as to penetrate the wall of the case 40 , and the sound generator 81 is attached to the outer surface of the case 40 .
Even in the case where the flow path switching mechanism 7 is provided in the pilot relay 6 in this manner, the "auto" and "manual" states can be easily distinguished.

Second Embodiment
The flow path switching mechanism according to the present invention can be configured as shown in Figures 9 and 10. In Figures 9 and 10, members that are the same as or equivalent to those described with reference to Figures 1 to 6 are given the same reference numerals and detailed descriptions thereof will be omitted as appropriate.
The valve element 56 of the flow path switching mechanism 7 shown in Fig. 9 has a cylinder 91 at its tip. A fixed throttle 66 is provided inside the cylinder 91. The cylinder 91 is formed so as to be inserted into the control pressure passage 50 in the housing 11 when the valve element 56 is in the first state. A minute gap, approximately the size of a clearance, is formed between the cylinder 91 and the wall surface of the control pressure passage 50.

In this embodiment, one end of the external communication passage 74 opens into the wall of the control pressure passage 50, facing the cylinder 91. Therefore, when the valve body 56 is in the first state, one end of the external communication passage 74 is substantially closed by the cylinder 91. The other end of the external communication passage 74 is connected to the sounding body 81.

In the flow path switching mechanism 7 according to this embodiment, in the auto mode, the valve body 56 is in the first state shown in FIG. 9, and the supply air from the air supply source PSPS passes only through the fixed throttle 66 and is sent to the control pressure passage 50. The nozzle back pressure PN created by the small flow rate of supply air sent to this control pressure passage 50 is supplied to the back pressure chamber 39 of the pilot relay 6 through the back pressure passage 48, and this nozzle back pressure PN is amplified by the pilot relay 6 and output as the air pressure signal PO, thereby automatically controlling the adjustment valve 2.

At this time, a portion of the supply air in the control pressure passage 50 leaks into the external communication passage 74 through the gap between the cylinder 91 and the wall of the control pressure passage 50, and passes through the external communication passage 74 to flow to the sounding body 81. At this time, the flow rate of the supply air passing through the external communication passage 74 is a flow rate of slight leakage, so even if this supply air flows into the sounding body 81, no sound will be generated from the sounding body 81.

On the other hand, in manual mode, the valve body 56 is in the second state as shown in FIG. 10. In this case, the supply air from the air supply source PS passes through not only the fixed throttle 66 but also the first and second outlet ports 62-64, and is sent to the control pressure passage 50 through the bypass passage 83 consisting of the gap between the tip of the valve body 56 and the inner surface of the valve body accommodating portion 51 (the first and second holes 51a, 51b), and the flow rate of the supply air sent to the control pressure passage 50 increases. This makes it possible to manually adjust the opening of the adjustment valve 2 by operating the pressure reducing valve 828 to change the supply air pressure P SUP.

In the manual mode, the cylinder 91 of the valve element 56 moves from the control pressure passage 50 into the valve element accommodating portion 51, so that one end of the external communication passage 74 is opened, allowing some of the supply air that has flowed into the valve element 56 to flow in. At this time, the flow rate of the supply air flowing through the external communication passage 74 is greater than the flow rate in the auto mode. Therefore, at this time, a large amount of air is blown into the sounding body 81, causing the sounding body 81 to generate sound.
Therefore, even if the flow path switching mechanism 7 is configured as shown in Figures 9 and 10, the "auto" and "manual" states can be easily distinguished, just as in the case of each of the above-mentioned embodiments.

1...positioner, 4...electro-pneumatic converter, 6...pilot relay, 7...flow path switching mechanism, 11...housing, 48...back pressure passage, 49...nozzle passage, 50...control pressure passage, 51...valve body housing, 52...first O-ring, 53...second O-ring, 56...valve body, 57...valve seat, 61...inlet, 62...first outlet, 63, 64...second outlet, 65...internal communication passage, 74...external communication passage, 81...sounding body, 66...fixed throttle, S...space.

Claims (3)

A flow path switching mechanism includes a valve body that is accommodated in a valve body accommodating portion formed within a wall thickness of a housing and can be moved forward and backward from outside the housing, and switches an outflow path of supply air supplied from outside the housing between a first state in which the valve body is seated on a valve seat provided in the valve body accommodating portion and a second state in which the valve body is separated from the valve seat,
The valve body is
an inlet for allowing the supply air to flow into the valve body;
an outlet port through which the supply air that has flowed into the valve body is discharged to the outside of the valve body;
an internal communication passage provided in the valve body that communicates the inlet and the outlet,
an external communication passage is formed in a thick wall portion of the housing, the external communication passage communicating between the valve body accommodating portion and the outside of the housing;
The external communication passage is
When the valve body is in a first state, the valve body is closed by an outer peripheral surface of the valve body, and when the valve body is in a second state, the valve body is opened to allow a portion of the supply air that has flowed into the valve body to pass therethrough;
a sound generating body connected to the external communication passage on an external side of the housing and configured to generate sound in response to air passing through the external communication passage; The flow path switching mechanism according to claim 1 ,
The supply air that has passed through the valve seat is guided to a passage that communicates with a nozzle passage and a back pressure passage,
a first O-ring and a second O-ring are attached between an outer circumferential surface of the tip portion of the valve body and an inner wall surface of the valve body accommodating portion,
The outlet is
a first outlet opening into a passage communicating with the nozzle passage and the back pressure passage, and a second outlet opening into a space partitioned by the first and second O-rings in the valve body accommodating portion,
The first outlet is provided with a fixed throttle,
When the valve body is in a first state, the supply air flowing in from the inlet passes through the internal communication passage and only the fixed throttle to reach a passage communicating with the nozzle passage and the back pressure passage,
a flow path switching mechanism characterized in that, when the valve body is in a second state, the supply air flowing in from the inlet passes through the internal communication passage, through the fixed orifice and the second outlet, and reaches a passage that communicates with the nozzle passage and the back pressure passage. A positioner including an electro-pneumatic converter that converts an electric signal into a pneumatic signal by utilizing air supplied from an outside source, a pilot relay that amplifies the pneumatic signal from the electro-pneumatic converter, and a housing that houses at least the electro-pneumatic converter,
The housing includes:
a passage for conducting an air pressure signal to the pilot relay;
A positioner, comprising: a valve body accommodating section formed in the passage, the valve body of the flow passage switching mechanism according to claim 1 or 2 accommodated therein so as to be operable to advance and retreat from outside the housing.

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