Patent Publication Number: US-2021164583-A1

Title: Flow control valve

Description:
TECHNICAL FIELD 
     The art disclosed in the present application relates to a flow control valve that adjusts a valve opening degree (opening area) using an electric drive device such as a motor to control the flow rate and pressure of various types of fluids such as gases and liquids. 
     BACKGROUND ART 
     A conventional flow control valve that adjusts a valve opening degree (opening area) using driving means such as a motor to control the flow rate and pressure of various types of fluids such as gases and liquids is disclosed, for example, in Patent Document 1. 
     Patent Document 1 discloses an electric valve including a valve housing in which a first opening and a second opening are formed; an annular valve seat part provided in communication with the second opening in the valve housing; a cylinder part provided in the valve housing so that its central axis is arranged on an axial line of a central axis of the valve seat part and so that one end thereof is opposite to the valve seat part with an interval; a valve member housed inside the cylinder part so as to be movable in a piston-like manner; a pressure balancing path provided to the valve housing or the valve member so as to cause a back pressure chamber on the other end side in the cylinder part formed by the space inside the cylinder part being divided by the valve member to communicate with the second opening; and a valve member moving means that moves the valve member to be seated on or unseat from the valve seat part, wherein an area in plan view of the inside of an annular tip part of the valve member is equal to an area in plan view of the back pressure chamber side of the valve member on the inside of the cylinder part. 
     CITATION LIST 
     Patent Documents 
     Patent Document 1: Japanese Patent No. 6043152. 
     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     A problem present in flow control valves using driving means such as a motor is the driving torque needed to move the valve member up and down and the backlash that occurs during movement up and down. The electric valve disclosed in Patent Document 1 has a problem in that, although it is possible to reduce the driving torque by having the area in plan view of the inside of the annular tip part of the valve member be equal to the area in plan view of the back pressure chamber side of the valve member on the inside of the cylinder part, backlash cannot be reduced. 
     The art disclosed in the present application was proposed in view of the above problem, and has an object of providing a flow control valve capable of reducing the driving torque of the motor which is driving means, and controlling backlash that occurs during upward and downward movement of the valve member. 
     Means for Solving the Problem 
     In order to achieve the above object, a flow control valve according to claim  1  is a flow control valve including a valve casing having a primary chamber that is an inlet section and a secondary chamber that is an outlet section; a valve seat provided inside the valve casing; a valve body that can be seated on the valve seat; a plunger that is continuous with the valve body; a drive unit, including at least a motor and a gear, configured to move the plunger along an axial direction of the plunger to switch between a closed state in which the valve body is seated on the valve seat and an open state in which the valve body is withdrawn from the valve seat; a pressure-receiving chamber provided between an upper surface of the valve body and the drive unit; and a conductive pathway, provided to the valve body along the axial direction of the plunger, that causes the secondary chamber and the pressure-receiving chamber to communicate, wherein the conductive pathway causes a pressure in the pressure-receiving chamber in which an upper surface of the valve body is present and a pressure in the secondary chamber in which a lower surface of the valve body is present to be approximately equal, and wherein the valve body is formed so that an area of the upper surface is slightly bigger than an area of the lower surface, whereby a force is constantly applied to the valve body in a valve opening direction. 
     The flow control valve according to claim  2  is the flow control valve according to claim  1 , wherein the valve body is composed of an upper valve body, an upper surface of which constitutes the lower surface of the pressure-receiving chamber; and a lower valve body, a lower surface of which constitutes the upper surface of the secondary chamber, the flow control valve further including a biasing member between the upper valve body and the lower valve body that biases the upper and lower valve bodies away from each other. 
     Effects of the Invention 
     In the flow control valve according to claim  1 , the pressure-receiving chamber on the upper surface side of the valve body (valve member) and the secondary side are connected with a conductive pathway (pressure balancing path) and the area of the upper surface of the valve body is made slightly bigger than the area of the lower surface of the valve body, whereby the force applied in an axial direction of the valve body is balanced in a state in which a slight force is applied upwardly (in a valve opening direction). (This is a state in which the valve body is raised toward the upper surface side). This makes it possible to reduce backlash occurring when the valve body moves up or down. Further, by reducing the difference in area between the upper surface of the valve body and the lower surface of the valve body to a required degree for reducing backlash, the difference in pressure applied to the upper surface and the lower surface of the valve body can be reduced, making it possible to reduce the driving torque needed when the valve body is to move up or down. Thus, upward and downward movement of the valve body becomes smooth, and the motor used in the drive unit can be made smaller. This makes it possible to provide a flow control valve capable of efficient flow control at a low cost. 
     In the flow control valve according to claim  2 , the valve body is divided in the axial direction into an upper valve body and a lower valve body, and a biasing member is provided therebetween to bias the two parts away from each other, so that if the secondary chamber side experiences an abnormal increase in pressure due to water hammer or the like when the flow control valve is closed and the lower valve body is seated on the valve seat, the lower valve body will rise against the biasing force of the biasing member to open the valve, whereby pressure can escape into the primary side so that damage to the secondary side can be prevented. In addition, when the valve body is seated on the valve seat by the drive unit when the valve is closed, and an excessive force (in the closing direction) is further applied to the valve body, the biasing member acts as a buffer, making it possible to prevent damage to components that may occur when excessive force is applied to the valve body (for example, damage to gears within the drive unit due to jamming of the gears, etc.). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a flow control valve according to a first embodiment of the present invention when the valve is closed; 
         FIG. 2  is a bottom view of the flow control valve; 
         FIG. 3  is a cross-sectional view of the flow control valve when the valve is open; 
         FIG. 4  is a magnified cross-sectional view describing a pressure introduction path provided to a valve body; 
         FIG. 5  is a cross-sectional view describing a pressure relief mechanism at a time of rising pressure on a secondary side; 
         FIG. 6  is a drawing showing a side view and a bottom view of a needle constituting a valve mechanism; 
         FIG. 7  is a drawing showing a top view, a side view (transparent view), and a bottom view of a needle nut constituting the valve mechanism; 
         FIG. 8  is a drawing showing a top view, a side view (transparent view), and a bottom view of a cylinder guide constituting the valve mechanism; 
         FIG. 9  is a drawing showing a top view, a side view (transparent view), and a bottom view of a cylinder constituting the valve mechanism; and 
         FIG. 10  is a drawing showing a top view, a side view (transparent view), and a bottom view of a cap constituting the valve mechanism. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First, a flow control valve  1  of an embodiment according to the present invention will be described with reference to the drawings. 
       FIG. 1  is a cross-sectional view of the flow control valve  1  in a closed state, and  FIG. 2  is a bottom view of the flow control valve  1  from below. The flow control valve  1  has a valve casing  2 . At one side of the bottom part of the valve casing  2 , a first connecting tube  3  protrudes in a lateral direction. On the lower side of the bottom part of the valve casing  2 , a second connecting tube  4  protrudes in a downward direction perpendicular to a central axis of the first connecting tube  3 . In an interior of the first connecting tube  3  there is formed a primary chamber  5  which constitutes an inlet side of a fluid. Meanwhile, in an interior of the second connecting tube  4  there is formed a secondary chamber  6  which constitutes an outlet side of the fluid. 
     The primary chamber  5  and the secondary chamber  6  are formed to gradually become narrower toward the interior. The interior of the valve casing  2  above the secondary chamber  6  is an opening of an approximately cylindrical shape and is provided with a valve chamber  8  that houses a valve mechanism  7  described below. An upper end portion of the valve chamber  8  is open, and at an upper end thereof, in other words above the valve casing  2 , a motor mechanism  10  is attached to the upper surface of the valve casing  2  by a screw or the like (not shown) via an upper lid  9 . The motor mechanism  10  is composed of a motor and drive unit not shown here, and drives a needle  17  described below to rotate. In the present embodiment, a stepper motor is employed as the motor, but the invention is not so limited, and a DC motor or a gear motor etc. may also be employed. 
     The valve chamber  8  is an opening composed of, formed continuously in order from above in the drawing, an upper opening  11  with a maximum diameter, a middle opening  12  with a diameter slightly smaller than that of the upper opening  11 , and a lower opening  13  forming a lower end and having a diameter smaller than that of the middle opening  12 , each of the openings being formed in a cylindrical shape. At a boundary between the upper opening  11  and the middle opening  12 , there is provided an upper opening edge  11   a . At a boundary between the middle opening  12  and the lower opening  13 , a valve seat  14  is provided so as to protrude toward the middle opening  12 . The valve seat  14  has an upper surface in the form of a circular arc, and is formed in an annular shape along an outer periphery of the lower opening  13 . As described below, when the flow control valve  1  is closed, a seating packing  15  is seated on the valve seat  14 . 
     Between the secondary chamber  6  and the lower opening  13  there is formed a needle support  16 . As shown in  FIG. 2  in which the flow control valve  1  is seen from below, The needle support  16  is composed of a center tube  16   a  having a through hole  16   b  at its center which a lower end of the needle  17  penetrates, and three ribs  16   c ,  16   c , and  16   c  provided at approximately equal intervals extending radially from the center tube  16   a  toward an inner peripheral surface of an upper opening of the secondary chamber  6 . Openings  16   d ,  16   d , and  16   d  between the ribs  16   c ,  16   c , and  16   c  are openings that provide communication between the valve chamber  8  (lower opening  13 ) with the secondary chamber  6 . 
     Next, a valve mechanism  7  of the flow control valve  1  according to the present invention will be described with reference to the drawings. 
     The valve mechanism  7  is composed of the needle  17  which is rotated by the motor mechanism  10 , a needle nut  18  provided with a female thread that engages a male thread of the needle  17 , a cylinder guide  19  that secures the needle nut  18  to the valve casing  2 , a cylinder  20  that is attached to a lower portion of the needle  17  and is able to slide up and down due to a sliding portion provided to a lower portion of the cylinder guide  19 , and a cap  22  that is attached to the cylinder  20  via a spring  21 . The needle nut  18 , the cylinder  20 , and the cap  22  are mounted so as to be penetrated by the needle  17 . In addition, the spring  21  is a compression spring that biases the cap  22  downward relative to the cylinder  20 . 
     Each of the components that constitute the valve mechanism  7  will be described in detail below. 
       FIG. 6  shows (A) a side view and (B) a bottom view seen from below of the needle  17 . As shown in  FIG. 6 , in the needle  17  there are formed, in order from above in a side view, each in a cylindrical shape with a different diameter, a gear section  17   a , a male thread section  17   b , a first needle recess  17   c , a second needle recess  17   d , a needle main body  17   e , a cylinder attachment section  17   f , a cap sliding section  17   g , a third needle recess  17   h , and a lower end support section  17   i . The gear section  17   a  engages with a gear (not shown) inside the motor mechanism  10 , whereby the needle  17  is controlled to rotate by the motor mechanism  10 . The male thread section  17   b  engages the female thread of the needle nut  18  as described above, whereby the needle  17  itself moves up and down by the rotation of the needle  17 . O-rings  30 ,  31  are fitted into the first needle recess  17   c  and the second needle recess  17   d  to maintain a sealed state between the needle  17  and the needle nut  18 . The cylinder attachment section  17   f  secures the cylinder  20  by being inserted therein. The cap sliding section  17   g  is inserted into the cap  22 . A stopping plate  27  is mounted in the third needle recess  17   h  to restrict downward movement of the cap  22  into which the needle  17  is inserted. 
       FIG. 7  shows (A) a top view seen from above, (B) a side view (transparent view), and (C) a bottom view seen from below of the needle nut  18 . As shown in  FIG. 7 , in the needle nut  18  there are formed, in order from above in a side view, a needle nut mounting section  18   a , a needle nut main body  18   b , a needle nut recess  18   c , and a needle nut lower tube section  18   d . The needle nut recess  18   c  is provided at a central portion of the needle nut main body  18   b . Apart from the needle nut mounting section  18   a , all of these sections are formed in a cylindrical shape. As shown in the top view of  FIG. 7  (A), the needle nut mounting section  18   a  is of a shape in which part of a cylinder is cut flat, and the needle nut  18  is mounted to the upper lid  9  by inserting the needle nut mounting section  18   a  into a mounting hole (not shown) formed in the upper lid  9  to fit the needle nut mounting section  18   a . Thus, in a state where the needle nut  18  is mounted to the upper lid  9 , rotary motion of the needle nut  18  is restricted. Further, the needle nut  18  is provided with cylindrical needle nut openings  18   e ,  18   f  with different opening diameters, which run through the needle nut  18  along its central axis in a vertical direction. Around an inner peripheral surface of the needle nut opening  18   e  is formed a female thread to engage with the male thread of the male thread section  17   b  of the needle  17 . An internal diameter of the needle nut opening  18   f  is slightly bigger than an outer diameter of the needle main body  17   e , so that when the needle  17  moves up and down, the needle main body  17   e  slides within the needle nut opening  18   f . An O-ring  28  is fitted into the needle nut recess  18   c  to maintain a sealed state between the needle nut  18  and the cylinder guide  19 . 
       FIG. 8  shows (A) a top view seen from above, (B) a side view (transparent view), and (C) a bottom view seen from below of the cylinder guide  19 . As shown in  FIG. 8 , in the cylinder guide  19  there are formed, in order from above in a side view, each in a cylindrical shape with a different diameter, a cylinder guide mounting section  19   a , a cylinder guide main body  19   b , a cylinder guide recess  19   c , a cylinder guide middle tube section  19   d , and a cylinder guide lower tube section  19   e . The cylinder guide recess  19   c  is provided at a central portion of the cylinder guide main body  19   b . Further, the cylinder guide  19  is provided with cylindrical cylinder guide openings  19   f ,  19   g ,  19   h  with different opening diameters, which run through the cylinder guide  19  along its central axis in a vertical direction. The cylinder guide opening  19   f  is formed to house the needle nut main body  18   b , and when the needle nut  18  is housed within the cylinder guide  19 , the O-ring  28  fit into the needle guide recess  18   c  maintains a sealed state between the needle nut  18  and the cylinder guide  19 , as described above. 
     An outer diameter of the cylinder guide main body  19   b  is slightly smaller than an inner diameter of the upper opening  11 , so that an O-ring  29  fit into the cylinder guide recess  19   c  maintains a sealed state between the cylinder guide  19  and an inner peripheral surface of the valve casing  2 . Further, since an edge at a lower end of the cylinder guide main body  19   b  abuts the upper opening edge  11   a , when the cylinder guide  19  is mounted in the valve casing  2 , downward movement of the cylinder guide  19  is restricted. Thus, the cylinder guide  19  is held within the upper opening  11  of the valve chamber  8  in a state of housing the needle nut  18 . An opening diameter of the cylinder guide opening  19   h  is set to be slightly bigger than an outer diameter of a cylinder main body  20   a  of the cylinder  20  to such a degree that the cylinder  20  described below is able to slide in a vertical direction. 
       FIG. 9  shows (A) a top view seen from above, (B) a side view (transparent view), and (C) a bottom view seen from below of the cylinder  20 . As shown in  FIG. 9 , in the cylinder  20  there are formed, in order from above in a side view, each in a cylindrical shape with a different diameter, a cylinder main body  20   a , a first cylinder recess  20   b , a cylinder lower section  20   c , and a second cylinder recess  20   d . The first cylinder recess  20   b  is provided at a central portion of the cylinder main body  20   a , and the second cylinder recess  20   d  is provided at a low position of the cylinder lower section  20   c.    
     Further, the cylinder  20  is provided with cylindrical cylinder openings  20   e ,  20   f  with different opening diameters, which run through the cylinder  20  along its central axis in a vertical direction. Further, in an inner peripheral surface of the cylinder opening  20   f  there are formed first cylinder grooves  20   g  that extend outwardly at an upper end portion thereof to an inner peripheral surface of the cylinder opening  20   e , and first cylinder grooves  20   h  that communicate with the first cylinder grooves  20   g  and extend downwardly along the inner peripheral surface of the cylinder opening  20   f  to a lower end surface of the cylinder  20 . In the present embodiment, as shown in  FIG. 9 , first communicating grooves  23  consisting of the first cylinder grooves  20   g  and the first cylinder grooves  20   h  are formed at three locations at approximately equal intervals in the inner surface of the cylinder opening  20   f.    
     The cylinder openings  20   e ,  20   f  are respectively formed so that the inner diameter of the cylinder opening  20   e  fits the outer diameter of the needle main body  17   e  and the inner diameter of the cylinder opening  20   f  fits the outer diameter of the cylinder attachment section  17   f  of the needle  17 , and the cylinder  20  is attached to the needle  17  in a state of having the needle  17  inserted therein. In addition, O-rings  32 ,  33  are respectively fitted into the first cylinder recess  20   b  and the second cylinder recess  20   d  to maintain a sealed state respectively between the cylinder  20  and the cylinder guide  19  and between the cylinder  20  and the cap  22 . 
       FIG. 10  shows (A) a top view seen from above, (B) a side view (transparent view), and (C) a bottom view seen from below of the cap  22 . As shown in  FIG. 10 , in the cap  22  there are formed, in order from above in a side view, a cylindrical cap main body  22   a , an upper flange  22   b  of a truncated cone shape that expands outwardly toward the bottom, a cylindrical cap recess  22   c , and a lower flange  22   d  of a truncated cone shape that narrows inwardly toward the bottom. Fitted into the cap recess  22   c  is a ring-shaped seating packing  15  formed as an elastic member that is seated on the valve seat  14  when the flow control valve  1  is closed. 
     Further, the cap  22  is provided with cylindrical cap openings  22   e ,  22   f ,  22   g ,  22   h  with different opening diameters, which run through the cap  20  along its central axis in a vertical direction. An inner diameter of the cap opening  22   e  is slightly bigger than an outer diameter of the cylinder lower section  20   c , so that the cylinder lower section  20   c  is able to slide in a vertical direction within the cap opening  22   e . An inner diameter of the cap opening  22   f  is slightly smaller than the inner diameter of the cap opening  22   e , and is provided with the spring  21  that biases the cap  22  relative to the cylinder  20 . An inner diameter of the cap opening  22   g  is slightly bigger than an outer diameter of the cap sliding section  17   g  of the needle  17 , so that the cap sliding section  17   g  of the needle  17  is able to slide in a vertical direction within the cap opening  22   g . Further, in an inner surface of the cap opening  22   g  there are formed cap grooves  22   i  that extend in a vertical direction and constitute second communicating grooves  24 . In the present embodiment, the second communicating grooves  24  (cap grooves  22   i ), like the first communicating grooves  23 , are formed at three locations at approximately equal intervals in the inner surface of the cap opening  22   g.    
     Since the cylinder  20  as described above is attached to the needle  17 , and the cap  22  is attached to the cylinder  20  via the spring  21 , the cylinder  20  and the cap  22  move up and down as one together with the needle  17 , and since the flow control valve  1  opens and closes due to the seating packing  15  mounted in the cap  22 , the cylinder  20  and the cap  22  act together as a valve body  25  of the flow control valve  1 . 
     Next, the operation and effect of the valve mechanism  7  of the flow control valve according to the present invention configured as described above will be described. As mentioned above,  FIG. 1  is a cross-sectional view of the flow control valve  1  when the valve is closed, and  FIG. 3  is a cross-sectional view of the flow control valve  1  when the valve is open. 
     When closing the flow control valve  1 , the motor mechanism  10  rotates the needle  17  as indicated by arrow ( 1 ) in  FIG. 1 . The needle  17  moves downwardly as it rotates due to the needle nut  18  secured in the valve chamber  8  as described above, which also causes the valve body  25  consisting of the cylinder  20  and the cap  22  to move downwardly as it rotates, so that, as shown in  FIG. 1 , the seating packing  15  of the valve body  25  is seated on the valve seat  14 , whereby the flow control valve  1  closes. When opening the flow control valve  1 , as shown by arrows ( 1 ) and ( 2 ) in  FIG. 3 , the needle  17  is rotated by the motor mechanism  10  in the opposite direction to when the valve closes to move upwardly, which also causes the valve body  25  consisting of the cylinder  20  and the cap  22  to move upwardly, so that, as shown in  FIG. 3 , the seating packing  15  of the valve body  25  separates from the valve seat  14 , whereby the flow control valve  1  opens. As shown by arrow ( 3 ) in  FIG. 3 , fluid flows from the primary chamber  5  into the secondary chamber  6 . By using the motor mechanism  10  to seat the seating packing  15  of the valve body  25  on the valve seat  14 , or modify the degree of opening between the seating packing  15  of the valve body  25  and the valve seat  14  when opening the valve, the flow control valve  1  can control the flow rate of fluid flowing from the primary chamber  5  to the secondary chamber  6 . In addition, since the valve body  25  is composed of the cylinder  20  and the cap  22  (including the seating packing  15 ) via the spring  21 , the spring  21  acts as a buffer in the event that the needle  17  is rotated too far when closing the flow control valve  1 , which can prevent damage to components due to excessive rotation of the needle  17 . 
       FIG. 4  is a cross-sectional view that magnifies a portion of the valve body  25  (cylinder  20  and cap  22 ) of the flow control valve  1 . As described above, the cylinder  20  is provided with first communicating grooves  23  that run in a vertical direction of the cylinder  20 , and the cap  22  is provided with second communicating grooves  24  that run in a vertical direction of the cap  22 . Therefore, a pressure-receiving chamber  26  surrounded by the upper surface of the valve body  25  (the upper surface of the cylinder  20 ) and the cylinder guide opening  19   h  of the cylinder guide  19  is in communication with the secondary chamber  6  via the first communicating grooves  23  and the second communicating grooves  24 . Because of this, as indicated by arrow ( 1 ) in  FIG. 4 , fluid flows from the secondary chamber  6  into the pressure-receiving chamber  26 , so that the pressure in the pressure-receiving chamber  26  becomes approximately equal to the pressure in the secondary chamber  6 . In other words, the pressure in the pressure-receiving chamber  26  becomes approximately equal to a secondary side pressure. 
     In the flow control valve  1  according to the present invention, as shown in  FIG. 4 , a diameter PB of the upper surface of the valve body  25  is set to be slightly bigger than a diameter PA of the lower surface of the valve body  25 . Therefore, the valve body  25  will always be in a state in which a slight force is applied upwardly (in a valve opening direction). (This is a state in which the valve body  25  is raised toward the upper surface side). Thus, it is possible to reduce backlash occurring in the motor mechanism  10  when the valve body  25  moves up or down. This allows for the valve body  25  to be moved up and down smoothly. 
     In addition, by reducing backlash in the motor mechanism  10  to a required degree by means of the difference between the area (diameter PB) of the upper surface of the valve body  25  and the area (diameter PA) of the lower surface of the valve body  25 , the difference in pressure applied to the upper surface and the lower surface of the valve body  25  can be reduced. This makes it possible to reduce the activation torque needed to activate the motor mechanism  10  when the valve body  25  is to be moved up or down. 
     In this way, the flow control valve  1  according to the present invention allows for smooth upward and downward movement of the valve body  25 , which facilitates control of the flow rate of the fluid, and allows for miniaturization of the motor in the motor mechanism  10  due to the reduced activation torque of the motor, and thus makes it possible to provide a flow control valve capable of efficient flow control at a low cost. 
     Next, a case in which the secondary side connected to the secondary chamber  6  experiences an abnormal rise in pressure due to water hammer, etc. while the flow control valve  1  is closed will be described with reference to  FIG. 5 .  FIG. 5  is a cross-sectional view describing a pressure relief mechanism at a time of rising pressure on the secondary side in the flow control valve  1  according to the present invention. 
     When an abnormal rise in pressure due to water hammer etc. occurs in the secondary side connected to the secondary chamber  6  as indicated by arrow ( 1 ) in  FIG. 5  while the flow control valve  1  is closed, then, in the valve body  25 , the cap  22  will move upward against the biasing force of the spring  21 , as indicated by arrow ( 2 ) in  FIG. 5 . This causes the seating packing  15  of the valve body  25  to separate from the valve seat  14 , allowing for the pressure of the secondary side to escape into the primary chamber  5  which is the primary side, as indicated by arrow ( 3 ) in  FIG. 5 , thus preventing damage to the components of the secondary side, etc. In other words, by constituting the valve body  25  from the cylinder  20  and the cap  22  and having the cap  22  be attached to the cylinder  20  by the spring  21 , a pressure relief mechanism for when an abnormal rise in pressure occurs on the secondary side can easily be configured. In addition, as described above, the valve body  25  according to the present embodiment also successfully prevents damage to components due to excessive rotation of the needle  17  when closing the valve. 
     Here, the primary chamber  5  is an example of a primary chamber, the secondary chamber  6  is an example of a secondary chamber, the valve casing  2  is an example of a valve casing, the valve seat  14  is an example of a valve seat, the valve body  25  is an example of a valve body, the needle  17  is an example of a plunger, the motor mechanism  10  is an example of a drive unit, the pressure-receiving chamber  26  is an example of a pressure-receiving chamber, conductive pathways consisting of the first communicating grooves  23  and the second communicating grooves  24  are examples conductive pathways, the cylinder  20  is an example of an upper valve body, the cap  22  is an example of a lower valve body, and the spring  21  is an example of a biasing member. 
     An embodiment of the present invention has been described in detail above, but this is merely an example, and it should be understood that the present invention is not to be interpreted as equivalent to or limited by the specific descriptions in the above embodiment, but that it may be practiced in aspects to which various modifications, alterations, etc. based on the knowledge of a person skilled in the art have been added, and that such aspects, so long as they do not deviate from the spirit and scope of the present invention, all fall within the scope of the present invention. 
     For example, in the above embodiment, the valve body  25  is composed of the cylinder  20  and the cap  22 , but in a case where a separate pressure relief valve or the like is provided to the secondary side and there is no need to provide a pressure relief function to the valve body  25  as described above, the valve body  25  may be of a one-piece construction. This allows for a lower number of components, which may reduce production costs. 
     Further, in the above embodiment, the needle  17  is rotated by the motor mechanism  10  to cause the valve body  25  to move up or down together with the needle  17  to control the flow rate of the fluid, but the motor mechanism  10  may instead rotate the needle nut  18  to move the needle  17  up or down. In this case, since the needle  17  does not rotate, the valve body  25  can also be moved up or down without rotating. Thus, since the valve body  25  does not rotate in the fluid, the flow of fluid from the primary chamber  5  to the secondary chamber  6  can be stabilized. In addition, since wear on the O-rings fitted into the valve body  25  and the seating packing  15  can be reduced, this also improves maintainability. 
     Further, in the above embodiment, the conductive pathways consisting of the first communicating grooves  23  and the second communicating grooves  24  are provided at three locations, but the conductive pathways are not so limited, and may be provided at one location, or at four or more locations, so long as the pressure in the pressure-receiving chamber  26  becomes approximately equal to the secondary side pressure. Further, if it is possible to provide conductive pathways inside the needle  17 , then conductive pathways may be provided inside the needle  17 . 
     Further, in the above embodiment, a needle support  16  is provided, but depending on the shape of the needle  17 , this may not be necessary. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
       1  Flow control valve 
       2  Valve casing 
       5  Primary chamber 
       6  Secondary chamber 
       7  Valve mechanism 
       8  Valve chamber 
       10  Motor mechanism 
       14  Valve seat 
       15  Seating packing 
       17  Needle 
       18  Needle nut 
       19  Cylinder guide 
       20  Cylinder 
       22  Cap 
       23  First communicating groove 
       24  Second communicating groove 
       25  Valve body 
       26  Pressure-receiving chamber