Valve

Abstract

To provide a valve capable of accurately controlling secondary pressure.SOLUTION: Between a valve housing 10 and a valve body 51, an annular concave groove 541, which is provided between a secondary pressure chamber S2 and a back pressure chamber S3, and an annular elastic member 40, which is arranged in the annular concave groove 541 and seals the gap between the valve housing 10 and the valve element 51, are arranged, where an axial dimension L1 of the annular concave groove 541 is longer than an axial dimension L2 of the elastic member 40.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to valves, for example, valves for regulating the flow rate of a fluid. [Background technology]

[0002] BACKGROUND ART Valves are known in various fields that are provided in a flow path through which a fluid flows and are used to control the flow rate according to the opening degree of the valve.

[0003] For example, the valve in Patent Document 1 is a solenoid valve mainly composed of a valve housing, a valve seat, a valve element, a spring, and a solenoid. The valve element is arranged within the valve housing so as to be movable in the axial direction. Between the valve housing and the valve element are provided a control fluid supply chamber communicating with the primary pressure side of the flow path, a valve chest from which fluid communicating with the secondary pressure side of the flow path is discharged, and a back pressure chamber for the valve element on the axial opposite side of the valve chest from the control fluid supply chamber. The control fluid supply chamber and the back pressure chamber are in communication with each other via a through hole provided in the valve housing.

[0004] The valve seat is located between the control fluid supply chamber and the valve chamber. The valve disc is pressed away from the valve seat by a spring. The valve disc can move toward the valve seat in response to the electromagnetic force of the solenoid. The valve in Patent Document 1 maintains an open state in which the valve disc is away from the valve seat until it is de-energized or the electromagnetic force exceeds the biasing force of the spring. When the electromagnetic force exceeds the biasing force of the spring, the valve disc abuts against the valve seat and enters a closed state. The through-hole also balances the pressures in the control fluid supply chamber and the back pressure chamber, allowing forces acting on both axial sides of the valve disc to be offset. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7423169 (page 7, Figure 2) Summary of the Invention [Problem to be solved by the invention]

[0006] In the valve of Patent Document 1, the electromagnetic force changes depending on the amount of current flow, and thereby the opening between the valve disc and the valve seat is adjusted to control the flow rate of the fluid, thereby making it possible to adjust the secondary pressure in the valve chamber. However, with a valve such as that of Patent Document 1, there was a risk that fluid would leak from the radial gap between the valve disc and the valve housing, between the valve chamber and the space on the back side, making it impossible to accurately control the secondary pressure in the valve chamber.

[0007] The present invention has been made in view of these problems, and has as its object to provide a valve that can accurately control secondary pressure. [Means for solving the problem]

[0008] In order to solve the above problems, the valve of the present invention comprises: a valve housing having a valve seat; a valve element disposed within the valve housing and operable by a solenoid; a spring that biases the valve body in a direction opposite to the driving direction of the solenoid, a primary pressure chamber and a secondary pressure chamber arranged on both axial sides of the valve body and the valve seat, and a back pressure chamber arranged on the opposite side of the secondary pressure chamber from the former primary pressure chamber and communicating with the primary pressure chamber, A valve that controls the flow rate of a fluid passing through the primary pressure chamber and the secondary pressure chamber by opening and closing, an annular groove is provided in at least one of the valve housing and the valve body, the annular groove being between the secondary pressure chamber and the back pressure chamber; and an annular elastic member is disposed in the annular groove and seals the gap between the valve housing and the valve body, The axial dimension of the annular groove is longer than the axial dimension of the elastic member. With this, the gap between the secondary pressure chamber and the back pressure chamber between the valve housing and the valve body is sealed by the elastic member, allowing accurate control of the pressure in the secondary pressure chamber, and because the elastic member is allowed to move axially within the annular groove, the elastic member moves axially relative to the slippery side of the housing and valve body, reducing frictional resistance when the valve body is driven.

[0009] The elastic member may be an O-ring. This makes it easier to maintain the contact surface between the O-ring housing and the valve body perpendicular to the axial direction.

[0010] The surface opposite to the annular groove may be flat. This allows the elastic member to slide smoothly on the flat surface.

[0011] The flat surface may be longer than the stroke length of the valve body. This allows the elastic member to abut against the flat surface within the stroke range of the valve body, thereby maintaining a sealed state.

[0012] The annular groove may be provided in the valve body. With this, the elastic member is held on the valve body side where the annular groove is provided, which makes it easier to reduce frictional resistance between the housing and the elastic member.

[0013] The annular groove may be provided in the valve housing. With this, the elastic member is held on the valve housing side where the annular groove is provided, making it easier to reduce frictional resistance between the valve body and the elastic member. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a valve according to a first embodiment of the present invention. [Figure 2] FIG. 3 is an enlarged cross-sectional view of a main part showing the valve in a closed state. [Figure 3] FIG. 3 is an enlarged cross-sectional view of a main part showing the valve in an open state. [Figure 4] FIG. 1(a) is a schematic diagram showing a state in which the O-ring slides relative to the housing, and FIG. 1(b) is a schematic diagram showing a state in which the O-ring slides relative to the valve body. [Figure 5] 1(a) is a schematic diagram showing the state in which the O-ring is tilted relative to the valve body, and FIG. 1(b) is a schematic diagram showing the state in which the O-ring has returned to its normal state relative to the valve body. [Figure 6] FIG. 10 is a cross-sectional view of a valve according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A valve according to the present invention will be described below with reference to the following examples. [Example]

[0016] A valve according to a first embodiment will be described with reference to Figures 1 to 5. The valve in this embodiment is adopted as an expansion valve constituting a refrigeration cycle, and will be described as performing an opening and closing operation to adjust the flow rate of a refrigerant flowing down a flow path.

[0017] As shown in FIG. 1, the expansion valve 1 is mainly composed of a valve housing 10 as a housing, a valve element 51, and a solenoid 80.

[0018] The valve housing 10 is formed in a generally cylindrical shape from a metal or resin material. The valve housing 10 is provided with a primary pressure chamber S1, a secondary pressure chamber S2, and a back pressure chamber S3. The primary pressure chamber S1 is provided at the left end of the valve housing 10 and is connected to the primary pressure side of the refrigeration cycle. The secondary pressure chamber S2 is provided within the valve housing 10 and is connected to the secondary pressure side of the refrigeration cycle via a through-hole 10c. The back pressure chamber S3 is provided at the right end of the valve housing 10 and is connected to the internal space of the solenoid 80. In other words, the back pressure chamber S3 is formed by the valve housing 10 and the solenoid 80.

[0019] The valve housing 10 is provided with a through hole 10a that axially connects the primary pressure chamber S1 and the secondary pressure chamber S2, a through hole 10b that axially connects the secondary pressure chamber S2 and the back pressure chamber S3, a through hole 10c that extends radially from the secondary pressure chamber S2, and a communication hole 10d that axially connects the primary pressure chamber S1 and the back pressure chamber S3 at a position radially offset from the through holes 10a and 10b.

[0020] A cylindrical valve seat member 30 having a flange portion 30a at its left end is press-fitted and fixed from the left side into the inner peripheral surface that defines the through hole 10a. A tapered surface that expands in diameter toward the left is formed on the inner diameter side of the flange portion 30a (see FIG. 2). This tapered surface serves as a valve seat 31 with which a valve portion 53, described later, comes into contact and separates.

[0021] The valve element 51 is made of a metal or resin material. The valve element 51 is composed of a rod portion 52 which is a columnar body with a constant cross section, a valve portion 53 provided at the left end of the rod portion 52, and a large-diameter portion 54 which is provided on the rod portion 52 to the right of the valve portion 53 and has a larger diameter than the rod portion 52 and is in sliding contact with the inner circumferential surface 10e of the through-hole 10b. The right end of the rod portion 52 is inserted into and fixed to a movable iron core 84 of a solenoid 80. The valve element 51 and the valve seat 31 form a valve 70 which controls the flow rate and the opening and closing of the flow path as the valve element 51 moves relative to the valve housing 10.

[0022] The solenoid 80 is mainly composed of a casing 81 having an opening 81a that opens to the left in the axial direction, a substantially cylindrical center post 82 that is inserted into the opening 81a of the casing 81 from the left in the axial direction and is positioned between the inner diameter side of the casing 81 and the inner diameter side of the valve housing 10, a movable iron core 84 into which the right axial end of the rod portion 52 is inserted and fixed, a coil spring 85 that is disposed between the center post 82 and the movable iron core 84 and biases the movable iron core 84 to the right in the axial direction, which is the direction in which the valve 70 closes, and an excitation coil 86 that is wound around the outside of the center post 82 via a bobbin.

[0023] The center post 82 is formed from a rigid body that is a magnetic material such as iron or silicon steel, and includes a cylindrical portion 82b that extends axially and has an insertion hole 82c through which the rod portion 52 of the valve body 51 is inserted, and an annular flange portion 82d that extends radially outward from the outer peripheral surface of the left axial end of the cylindrical portion 82b.

[0024] Next, the sliding portion between the valve body 51 and the valve housing 10 will be described with reference to FIG.

[0025] As shown in FIG. 2, the sliding portion between the valve body 51 and the valve housing 10 is made up of the large diameter portion 54 of the valve body 51 and the inner circumferential surface 10e that forms the through hole 10b of the valve housing 10.

[0026] An annular groove 541 that opens in the radially outward direction is formed in the large diameter portion 54. In other words, the annular groove 541 is provided between the secondary pressure chamber S2 and the back pressure chamber S3.

[0027] An inner peripheral surface 10e that defines the through hole 10b of the valve housing 10 is a flat surface that is flat in the axial and circumferential directions.

[0028] An O-ring 40 serving as an elastic member is disposed in the annular groove 541. The O-ring 40 is compressed between a bottom surface 541a of the annular groove 541 and an inner circumferential surface 10e of the through-hole 10b. This seals the gap between the secondary pressure chamber S2 and the back pressure chamber S3, preventing fluid from moving between the secondary pressure chamber S2 and the back pressure chamber S3, and enabling accurate control of the pressure in the secondary pressure chamber S2.

[0029] The axial dimension L1 of the annular groove 541 is longer than the axial dimension L2 of the O-ring 40 compressed between the bottom surface 541a of the annular groove 541 and the inner circumferential surface 10e of the through hole 10b (L1>L2). Note that, although the axial dimension L1 of the annular groove 541 in this embodiment is approximately twice the axial dimension L2 of the O-ring 40, the ratio can be freely changed as long as the axial dimension L1 is longer than the axial dimension L2.

[0030] Furthermore, the crushing allowance of the O-ring 40 relative to the bottom surface 541a of the annular groove 541 is larger than the crushing allowance relative to the inner circumferential surface 10e of the through-hole 10b.

[0031] Next, the operation of the valve element 51, that is, the opening and closing operation of the valve 70 will be described with reference to FIGS.

[0032] First, we will explain the state when the expansion valve 1 is not energized. As shown in Figures 1 and 2, when the expansion valve 1 is not energized, the movable iron core 84 is pressed axially rightward by the biasing force of the coil spring 85, the valve portion 53 abuts against the valve seat 31, and the valve 70 is closed.

[0033] At this time, the valve element 51 is acted upon by a biasing force (Fsp1) of the coil spring 85 to the right in the axial direction, a force (FP1) due to the pressure of the fluid on the valve element 51, and a force (FP2) due to the pressure of the fluid on the valve element 51 to the left in the axial direction. In other words, with the rightward direction being positive, a force Frod = Fsp1 + FP1 - FP2 acts on the valve element 51.

[0034] The force (FP1) when the valve 70 is closed is the force due to the pressure of the fluid in the primary pressure chamber S1 acting on the effective pressure-receiving surface A of the valve portion 53 and the pressure of the fluid in the secondary pressure chamber S2 acting on the effective pressure-receiving surface B of the large diameter portion 54.

[0035] On the other hand, force (FP2) is a force due to the pressure of the fluid in the secondary pressure chamber S2 acting on the effective pressure-receiving surface A of the valve portion 53 and the pressure of the fluid in the back pressure chamber S3 acting on the effective pressure-receiving surface B of the large diameter portion 54.

[0036] In this embodiment, the effective pressure-receiving surface A of the valve portion 53 and the effective pressure-receiving surface B of the large-diameter portion 54 are formed to have the same area. Furthermore, the primary pressure chamber S1 and the back pressure chamber S3 are in communication with each other through the communication hole 10d and are at the same pressure. Therefore, the effects of the pressures of the fluids in the primary pressure chamber S1, the secondary pressure chamber S2, and the back pressure chamber S3 acting on both sides of the valve body 51 in the movement direction are canceled out.

[0037] Next, we will explain the outline of the energized state of the expansion valve 1. As shown in Figures 1 and 3, when the expansion valve 1 is energized, that is, during normal control, or so-called duty control, and the electromagnetic force (Fsol) generated by applying current to the solenoid 80 exceeds the force Frod (Fsol > Frod), the movable core 84 is attracted toward the center post 82, that is, to the left in the axial direction, and the valve element 51 fixed to the movable core 84 moves axially leftward together with it, causing the valve portion 53 of the valve element 51 to separate from the valve seat 31 in the valve housing 10, and the valve 70 is opened.

[0038] At this time, an electromagnetic force (Fsol) acts on the valve element 51 in the axial left direction, and a force Frod acts on the valve element 51 in the axial right direction (that is, the force Frod-Fsol acts on the valve element 51, with the rightward direction being positive).

[0039] Next, the state of the O-ring 40 when the valve element 51 moves will be described. Note that, here, an example will be described in which the valve element 51 moves to the left from the position in the valve closed state. Also, an example will be given in which the O-ring 40 abuts against the left side surface 541b of the annular groove 541 when the valve element 51 is in the valve closed state.

[0040] 4(a), it is assumed that the coefficient of friction of the inner circumferential surface 10e of the through hole 10b of the valve housing 10 is lower than the coefficient of friction of the bottom surface 541a of the annular groove 541 of the valve body 51. In FIG.

[0041] 4(a), when the valve disc 51 moves to the left from the position in the valve closed state (see the white arrow), the O-ring 40 slides (see the black arrow) along the inner circumferential surface 10e of the valve housing 10, whose outer diameter side has a relatively low coefficient of friction, and moves to the left together with the valve disc 51. In other words, the position of the O-ring 40 relative to the valve housing 10 changes, without changing the position of the O-ring 40 relative to the valve disc 51.

[0042] 4(b), it is assumed that the coefficient of friction of the inner circumferential surface 10e of the through hole 10b of the valve housing 10 is higher than the coefficient of friction of the bottom surface 541a of the annular groove 541 of the valve body 51. In FIG.

[0043] 4(b), when the valve element 51 moves to the left from the closed position (see the white arrow), the O-ring 40 slides along the bottom surface 541a of the annular groove 541 of the valve element 51, the inner diameter side of which has a relatively low coefficient of friction (see the black arrow), and the axial position of the O-ring 40 does not change. In other words, the position of the O-ring 40 relative to the valve element 51 changes, but the position of the O-ring 40 relative to the valve housing 10 does not change.

[0044] In this way, relative axial movement of the O-ring 40 is permitted within the annular groove 541, so that the O-ring 40 moves relative to the valve housing 10 or the valve body 51, whichever is more slippery, in the axial direction, thereby reducing frictional resistance when the valve body 51 is driven.

[0045] Furthermore, the inner circumferential surface 10e of the through hole 10b of the valve housing 10, which faces the annular groove 541, is flat, so that the O-ring 40 can slide smoothly in the axial direction along the inner circumferential surface 10e.

[0046] Furthermore, the axial dimension L3 of the inner peripheral surface 10e is longer than the maximum stroke length L4 of the valve body 51 (see Figure 4(a)), so that the O-ring 40 can be kept in contact with the inner peripheral surface 10e within the stroke range of the valve body 51, thereby maintaining sealing performance.

[0047] Furthermore, since the O-ring 40 is disposed within the annular groove 541, even if the axial position of the O-ring 40 relative to the valve body 51 changes over time, it abuts against the left and right side surfaces 541b, 541c of the annular groove 541, preventing it from coming out of the annular groove 541.

[0048] Also, the O-ring 40 is held on the valve body 51 side where the annular groove 541 is provided. That is, the O-ring 40 is designed based on the bottom surface 541a of the annular groove 541, so the crushing allowance against the bottom surface 541a of the annular groove 541 is larger than the crushing allowance against the inner circumferential surface 10e of the through hole 10b. Therefore, the pressing force against the valve body 51 side tends to be relatively large, making the O-ring 40 more likely to slide against the inner circumferential surface 10e, and making it easier to reduce the frictional resistance between the O-ring 40 and the inner circumferential surface 10e (easiness of achieving the state shown in FIG. 4(a)).

[0049] Furthermore, since the portion of the O-ring 40 that abuts against the side surface 541b of the annular groove 541 is close to the bottom surface 541a of the annular groove 541, the O-ring 40 is less likely to get caught between the valve housing 10 and the valve element 51 when the valve element 51 moves.

[0050] In such an expansion valve 1, as shown in Figure 5(a), when the valve body 51 moves to the left from the closed position, the upper part of the O-ring 40 on the page moves together with the valve body 51, while the lower part of the O-ring 40 on the page does not move and moves relative to the valve body 51, which may occur momentarily.

[0051] 5(b), since it is the O-ring 40, the elastic restoring force tends to act in the axial direction, causing the portion of the O-ring 40 on the lower side of the page to slide to the left, and the O-ring 40 returns to a state approximately perpendicular to the axial direction of the valve body 51. In other words, the O-ring 40 tends to maintain the contact surface with the inner circumferential surface 10e of the through hole 10b of the valve housing 10 and the contact surface with the bottom surface 541a of the annular groove 541 of the valve body 51 perpendicular to the axial direction.

[0052] In addition, Figure 5 illustrates an example in which the portion of the O-ring 40 on the lower side of the paper moves to the left due to the elastic restoring force, but depending on the friction coefficient, the portion of the O-ring 40 on the upper side of the paper may move to the right due to the elastic restoring force.

[0053] Furthermore, in this embodiment, an example was given in which the movement pattern of the O-ring 40 differed depending on the difference in the coefficient of friction between the inner circumferential surface 10e of the through hole 10b in the valve housing 10 and the bottom surface 541a of the annular groove 541 in the valve body 51, but to stably perform the operation shown in Figures 4(a) and 4(b), it is desirable that the O-ring 40 slides only on one side, either the inner or outer periphery, around the circumferential direction. To achieve this, it is preferable to make the coefficient of friction between the inner circumferential surface 10e and the bottom surface 541a differ by 0.03 or more, and more preferably, by 0.05 or more.

[0054] Furthermore, although only the case where the valve body 51 moves from right to left has been described, it goes without saying that the O-ring 40 also moves in the same manner as described above when the valve body 51 moves from left to right. [Example]

[0055] Next, a valve according to a second embodiment will be described with reference to Fig. 6. Note that a description of the same configuration as in the first embodiment will be omitted.

[0056] 6, in the expansion valve 100 of the second embodiment, a valve body 151 is made up of a rod 152 and a valve body member 153. The valve body member 153 is press-fitted and fixed to the left end of the rod 152.

[0057] The valve body member 153 includes, from the left, a valve portion 153a, a small diameter portion 153b, and a large diameter portion 153c, and is provided with a through hole 153d that penetrates in the axial direction and a branch hole 153e that penetrates radially from the right end of the through hole 153d. The right end opening of the through hole 153d is closed by the rod 152. The branch hole 153e is always located in the back pressure chamber S3 within the stroke range of the valve body 151.

[0058] The primary pressure chamber S1 and the back pressure chamber S3 are in communication with each other through the through hole 153d and the branch hole 153e. That is, the through hole 153d and the branch hole 153e form a communication passage between the primary pressure chamber S1 and the back pressure chamber S3. Because a communication passage is formed in the valve body 151 in this way, there is no need to provide a communication passage in the valve housing 110, allowing for a compact structure.

[0059] An annular groove 141 is formed between the valve housing 110 and the center post 182 of the solenoid 180. Specifically, the groove 111 is formed in the valve housing 110 and is open to the right side and the inner diameter side. The right opening of the groove 111 is closed by the end face of the center post 182 that is connected to the valve housing 110. This forms the annular groove 141 that is open to the inner diameter side.

[0060] The annular groove 141 is disposed between the secondary pressure chamber S2 and the back pressure chamber S3. An O-ring 140 is disposed in the annular groove 141 to seal the space between the secondary pressure chamber S2 and the back pressure chamber S3. The axial dimension of the annular groove 141 is longer than the axial dimension of the O-ring 140.

[0061] An outer peripheral surface 153f of the large diameter portion 153c facing the opening of the annular recessed groove 141 is formed into a flat surface that is flat in the axial and circumferential directions.

[0062] As in the first embodiment, when the valve body 151 moves, the O-ring 140 moves axially against the slippery one of the bottom surface 141a of the annular groove 141 in the valve housing 110 and the outer peripheral surface 153f of the large diameter portion 153c of the valve body 151, thereby reducing frictional resistance.

[0063] Also, the O-ring 140 is configured to be held on the valve housing 110 side where the annular groove 141 is provided. That is, because the O-ring 140 is designed based on the bottom surface 141a of the annular groove 141, the pressing force toward the valve housing 110 side tends to be relatively large, and the O-ring 140 tends to slide easily against the outer peripheral surface 153f of the large diameter portion 153c. That is, the O-ring 140 does not move relative to the valve housing 110, but tends to move relative to the valve body 151. This makes it easy to reduce frictional resistance between the O-ring 140 and the outer peripheral surface 153f of the large diameter portion 153c.

[0064] Furthermore, the annular groove 141 is formed by two axially separated members, namely, the valve housing 110 and the solenoid 180. This makes it easy to install the O-ring 140 in the annular groove 141 because the O-ring 140 can be inserted into the groove 111 of the valve housing 110 from the right side before connecting the valve housing 110 and the solenoid 180.

[0065] In addition, in the second embodiment, a recess 182a that opens to the left is formed on the inner periphery of the left end of the center post 182, and a part of the large diameter portion 153c of the valve body member 153 can be placed inside the recess 182a. This allows the axial length of the expansion valve 100 to be shortened.

[0066] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0067] For example, in the first and second embodiments, the valves are described as being configured to be applied to a refrigeration cycle, but the present invention is not limited to this and may be applied to a hydraulic circuit or may be modified as appropriate.

[0068] Furthermore, in the above-described first and second embodiments, the fluid passing through the valve is described as a heat transfer medium, but this is not limited to this, and the type of fluid may be changed as appropriate, such as water or air, the state of the fluid may be changed as appropriate, such as air, liquid, or mist, and the type and state of the fluid may be mixed.

[0069] In addition, in the first and second embodiments, the valve has been described as being configured to be used as an expansion valve, but is not limited to this and may be used as, for example, an on-off valve or a flow rate adjusting valve. Also, the valve may be a pressure reducing valve other than an expansion valve.

[0070] Furthermore, in the first and second embodiments, the valves are of a normally closed type that is in a closed state when de-energized, but this is not limiting and the valves may be of a normally open type that is in an open state when de-energized.

[0071] In addition, in the first and second embodiments, the effective pressure-receiving surface of the valve portion and the effective pressure-receiving surface of the sliding portion are described as having the same area, but this is not limiting and they may be different. Even with this configuration, the force acting on the valve body can be reduced by the area where the effective pressure-receiving surface of the valve portion and the effective pressure-receiving surface of the sliding portion overlap.

[0072] In addition, in the above-described first and second embodiments, the elastic member is an O-ring having a circular cross section, but this is not limited to this. For example, the elastic member may be an elliptical cross section, a K-shaped cross section, an X-shaped cross section, or a lip seal. [Explanation of symbols]

[0073] 1 Expansion valve (valve) 10 Valve housing (housing) 10b Through hole 10d communication hole 10e Inner surface (flat surface) 31 Valve seat 40 O-ring (elastic member) 51 Valve body 52 Rod section 53 Valve section 54 Large diameter section 70 valves 80 Solenoid 85 coil spring (spring) 541 Circular groove S1 Primary pressure chamber S2 Secondary pressure chamber S3 Back pressure chamber

Claims

1. a valve housing having a valve seat; a valve element disposed within the valve housing and operable by a solenoid; a spring that biases the valve body in a direction opposite to the driving direction of the solenoid, a primary pressure chamber and a secondary pressure chamber arranged on both axial sides of the valve body and the valve seat, and a back pressure chamber arranged on the opposite side of the secondary pressure chamber from the former primary pressure chamber and communicating with the primary pressure chamber, a valve that controls a flow rate of a fluid passing through the primary pressure chamber and the secondary pressure chamber by opening and closing the valve, an annular groove is provided in at least one of the valve housing and the valve body, the annular groove being between the secondary pressure chamber and the back pressure chamber; and an annular elastic member is disposed in the annular groove and seals the gap between the valve housing and the valve body, The axial dimension of the annular groove is longer than the axial dimension of the elastic member.

2. 2. The valve of claim 1, wherein the resilient member is an O-ring.

3. 2. The valve according to claim 1, wherein the surface opposite to the annular groove is flat.

4. 4. The valve of claim 3, wherein the flat surface is longer than the stroke length of the valve body.

5. The valve according to claim 1 , wherein the annular groove is provided in the valve body.

6. 2. The valve of claim 1, wherein the annular groove is provided in the valve housing.

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