Patent Description:
Gas solenoid valves are provided to open and close channels through which gas flows; as an example, a solenoid valve such as that disclosed in Patent Literature (PTL <NUM>) is known.

PTL <NUM>: <CIT>. <CIT> discloses a valve element that can be automatically aligned with respect to a pilot valve hole. <CIT> discloses a solenoid valve comprising an armature that can freely ride within a tubular member and comprises a passage extending axially along its periphery to permit free passage of flow around it. <CIT> discloses a self-modulating control valve which meters fluid flow through valving ports to a pressure stabilizing chamber.

For example, there are cases where a solenoid valve is provided on a gas tank, and the solenoid provided on the gas tank is used as follows. Specifically, in the case of filling the gas tank with gas, gas pressure causes a main valve to be lifted off a valve seat, thus opening a channel. At this time, chattering occurs at the main valve, etc., causing various problems such as noise, damage to a seat, and contamination attributable to wear and tear.

Thus, the present invention has an object to provide a gas solenoid valve in which the occurrence of chattering at a main valve body is minimized.

A gas solenoid valve according to the present invention is defined in claim <NUM> of the appended claims.

According to the present invention, with the damping chamber, movement of the main valve body can be restricted, in other words, vibrations of the main valve body can be damped. This makes it possible to minimize the occurrence of chattering at the main valve body.

In the above-described invention, the gas solenoid valve includes a seat piston that is inserted through the main valve body, receives the biasing force of the biasing member, and biases the main valve body to the closed position, a pilot passage connecting the first port and the second port is formed in the main valve body, the seat piston is capable of moving between a pilot closed position thereof closing the pilot passage and a pilot open position thereof opening the pilot passage, the electromagnetic drive device generates the excitation force to cause the seat piston to move to the pilot open position, to cause the main valve body to move to the open position, the damping chamber is formed in a position located in the opening direction from the seat piston and adjacent to the seat piston, and the biasing member is disposed in the damping chamber.

According to the above configuration, a chamber in which the biasing member is housed is used as the damping chamber, meaning that there is no need to form another damping chamber to damp vibrations of the main valve body. Therefore, it is possible to avoid an increase in the size of the gas solenoid valve.

In the above-described invention, the electromagnetic drive device includes: a plunger through which the seat piston is inserted in a manner to be movable in conjunction; a stationary pole disposed facing the plunger; and a solenoid that provides the excitation force to the plunger to attract the plunger to the stationary pole, and the damping chamber is formed in the plunger to position the biasing member between the seat piston and the stationary pole, and gas is introduced into and discharged from the damping chamber through a gap between the seat piston and the plunger.

According to the above configuration, the amount of gas to be introduced into and discharged from the damping chamber is limited using the gap, and thus it is possible to minimize abrupt changes in the volume of the damping chamber, minimizing vibrations of the main valve body, in other words, minimizing the occurrence of chattering at the main valve body. Furthermore, the amount of gas to be introduced into and discharged from the damping chamber can be changed according to the width of the gap, and thus it is possible to adjust the damping force of the damping chamber according to the width of the gap. Therefore, by adjusting the width, it is possible to minimize the occurrence of chattering at the main valve body more effectively.

In the above-described invention, it is preferable that the gas solenoid valve further include a stopper that limits an amount of movement of the main valve body in the opening direction.

According to the above configuration, it is possible to minimize damage to a biasing member that occurs due to excessive stroke of the main valve body.

With the present invention, it is possible to minimize the occurrence of chattering at the main valve body.

The above object, other objects, features, and advantages of the present invention will be made clear by the following detailed explanation of preferred embodiments with reference to the attached drawings.

Hereinafter, a gas solenoid valve <NUM> according to the present embodiment of the present invention will be described with reference to the drawings. Note that the concept of directions mentioned in the following description is used for the sake of explanation and is not intended to limit the orientations, etc., of elements according to the present invention to these directions. The gas solenoid valve <NUM> described below is merely one embodiment of the present invention. Thus, the present invention is not limited to the embodiment and may be subject to addition, deletion, and alteration within the scope of the claims.

A gas solenoid valve <NUM> illustrated in <FIG> is provided on a gas tank or the like that can hold a high pressure gas, and the gas solenoid valve <NUM> enables gas filling and discharge by opening and closing a channel. Note that the gas tank is one example for which the gas solenoid valve <NUM> is used, and a subject for which the gas solenoid valve <NUM> is used is not necessarily limited to the gas tank. Specifically, the gas solenoid valve <NUM> is provided in a channel required to allow gas to flow in both directions. The gas solenoid valve <NUM> having such a function is configured as follows.

Specifically, the gas solenoid valve <NUM> mainly includes a housing <NUM>, a guide member <NUM>, a main valve body <NUM>, a seat piston <NUM>, and an electromagnetic drive device <NUM>. In the housing <NUM>, a valve chamber <NUM> in the approximate shape of a circular column having a closed end is formed, and an opening part of the valve chamber <NUM> is covered by a lid body <NUM>. Furthermore, a first channel <NUM> leading to a first port <NUM> and a second channel <NUM> leading to a second port <NUM> are formed in the housing <NUM>. The first channel <NUM> is open at a bottom 21a of the valve chamber <NUM> via a valve port <NUM>, and the second channel <NUM> is open in a side surface of the valve chamber <NUM>. The housing <NUM> configured as just described houses the guide member <NUM>, the main valve body <NUM>, the seat piston <NUM>, and the electromagnetic drive device <NUM> in the valve chamber <NUM> in order to open and close the valve port <NUM>.

The guide member <NUM> is formed in the approximate shape of a circular cylinder, and at least a portion of the outer peripheral surface of the guide member <NUM> (in the present embodiment, two portions separated from each other by <NUM> degrees in the peripheral direction) is formed to be flat. The guide member <NUM> shaped as just described fits into the valve chamber <NUM> with one end in contact with the bottom 21a of the valve chamber <NUM>, and forms one pair of gaps <NUM>, <NUM> with the housing <NUM>. Furthermore, two communication channels <NUM>, <NUM> are formed at one end of the guide member <NUM>, as illustrated in <FIG>. The two communication channels <NUM>, <NUM> extend in opposite directions along the radius of an inner hole 12a of the guide member <NUM> and connect the valve port <NUM> and the gaps <NUM>, <NUM>. Similarly, two communication channels <NUM>, <NUM> are formed at the other end of the guide member <NUM>, and the gaps <NUM>, <NUM> and the inner hole 12a of the guide member <NUM> are connected by communication channels <NUM>, <NUM>. Furthermore, the main valve body <NUM> is inserted into the inner hole 12a, as illustrated in <FIG>.

The main valve body <NUM> is formed in the approximate shape of a circular cylinder having a closed end with a base end portion 13b larger in diameter than a leading end portion 13a. The base end portion 13b of the main valve body <NUM> shaped as just described fits into the inner hole 12a and can move axially along the inner hole 12a of the guide member <NUM>. Furthermore, the main valve body <NUM> can be in a closed position such as that illustrated in <FIG> and includes a seat member 13c on a leading end surface. When the main valve body <NUM> is in the closed position, the seat member 13c is seated on a valve seat <NUM>, and thus the valve port <NUM> is closed. On the other hand, when the main valve body <NUM> is positioned in an open position by moving axially in the opposite direction, the seat member 13c separates from the valve seat <NUM>, and thus the valve port <NUM> is opened.

The main valve body <NUM> configured as described above forms a housing space <NUM> with the guide member <NUM> in order to house a first coil spring <NUM>. Specifically, in the guide member <NUM>, the inner hole 12a has one end portion 12b formed smaller in diameter than a remaining portion 12c, and the leading end portion 13a of the main valve body <NUM> is inserted through the one end portion 12b. Thus, the housing space <NUM> in the approximate shape of a circular ring is formed between the leading end portion 13a of the main valve body <NUM> and the guide member <NUM>, and the first coil spring <NUM> is housed in the housing space <NUM>. The first coil spring <NUM> is what is called a compression coil spring and provides, to the main valve body <NUM>, a biasing force in an opening direction from the closed position to the open position. Note that the first coil spring <NUM> can be replaced by a leaf spring, an elastic body, a magnetic spring, a pneumatic spring, a pressing mechanism that uses an electrostatic force, or the like.

Furthermore, in the main valve body <NUM>, a pilot passage 13d is formed to allow communication between the first port <NUM> and the second port <NUM> when the main valve body <NUM> is in the closed position. The pilot passage 13d passes through the main valve body <NUM> along the axial line thereof, and when the main valve body <NUM> is seated, connects the valve port <NUM> and an inner hole 13e of the main valve body <NUM>. Moreover, in order to open and close the pilot passage 13d, the seat piston <NUM> is inserted through the inner hole 13e of the main valve body <NUM> in such a manner as to be axially movable and located adjacent to the housing space <NUM>.

The seat piston <NUM> is formed in the approximate shape of a circular column, and closes the pilot passage 13d by inserting a leading end 14a of the seat piston <NUM> into a seat portion 13f of the pilot passage 13d and causing the leading end 14a to be seated. In other words, as a result of the seat piston14 being positioned in a pilot closed position, the pilot passage 13d is closed. Furthermore, the seat piston <NUM> can move from the pilot closed position to a pilot open position along the axial line of the seat position <NUM>, and when the seat piston <NUM> moves, the leading end 14a separates from the seat portion 13f. Accordingly, the pilot passage 13d is opened, and the valve port <NUM> and the inner hole 13e of the main valve body 13e are brought into communication. Furthermore, a plurality of slits (in the present embodiments, two slits) 14b, 14b are formed in the outer peripheral surface of the seat piston <NUM>, and the slits 14b, 14b form channels connecting the pilot passage 13d and the aforementioned two communication channels <NUM>, <NUM> when the pilot passage 13d is open. The seat piston <NUM> configured as just described has a base end portion 14c protruding from the main valve body <NUM>, and the electromagnetic drive device <NUM> is provided on this protrusion.

The electromagnetic drive device <NUM> includes a plunger <NUM>, a stationary pole <NUM>, and a solenoid <NUM>. The plunger <NUM> is a member in the approximate shape of a circular cylinder that is made of a magnetic material, and the base end portion 14c of the seat piston <NUM> is inserted through an inner hole 41a of the plunger <NUM>. Furthermore, in the inner hole 41a, a leading end portion 41b is formed smaller in diameter than the base end portion 41c, and accordingly a base end 14d of the seat piston <NUM> is formed larger in diameter than the remaining portion. Thus, the plunger <NUM> engages the base end 14d of the seat piston <NUM> at the leading end portion of the inner hole 41a of the plunger <NUM> and is configured to move in conjunction with the seat piston <NUM>. The stationary pole <NUM> is provided so as to face the plunger <NUM> configured as just described.

The stationary pole <NUM> is a member in the approximate shape of a circular column that is made of a ferromagnetic material and is disposed apart from the base end of the plunger <NUM> in one axial direction. The outer diameter of a leading end portion 42b of the stationary pole <NUM> disposed as just described is approximately equal to the outer diameter of the plunger <NUM>, and a sleeve <NUM> is provided surrounding the leading end portion 42b of the stationary pole <NUM> and the plunger <NUM>. The sleeve <NUM> is a member in the approximate shape of a circular cylinder that is made of a non-magnetic material and is configured so that the plunger <NUM> can move axially in the sleeve <NUM>. The solenoid <NUM> is provided surrounding the sleeve <NUM> configured as just described.

The solenoid <NUM> is formed in the approximate shape of a circular column and can generate an excitation force for the plunger <NUM> by passing an electric current to a coil 43b wound on a bobbin 43a. Specifically, the solenoid <NUM> can excite the plunger <NUM> so that the plunger <NUM> is attracted to the stationary pole <NUM>, and thus can move the seat piston <NUM>, which moves in conjunction with the plunger <NUM>, to the pilot open position by the attraction. Furthermore, in order to provide a biasing force opposing the excitation force to the plunger <NUM> (more specifically, to the plunger <NUM> via the seat piston <NUM>), a second coil spring <NUM> is provided on the plunger <NUM>.

The second coil spring <NUM>, which is one example of the basing member, is what is called a compression coil spring and is inserted through the plunger <NUM>. Specifically, the inner hole 41a of the plunger <NUM> forms a spring housing chamber <NUM> together with a spring bearing recess 42a of the stationary pole <NUM> to be described later, and the second coil spring <NUM> is housed in the spring housing chamber <NUM>. The second coil spring <NUM> has one end fitted into the spring bearing recess 42a of the stationary pole <NUM> and the other end pressed against the base end 14d of the seat piston <NUM>. Therefore, the second coil spring <NUM> biases the plunger <NUM> via the seat piston <NUM> in one axial direction and pulls the plunger <NUM> away from the stationary pole <NUM>. Furthermore, as a result of being pressed against the seat piston <NUM>, the second coil spring <NUM> enables the plunger <NUM> and the seat piston <NUM> to move in conjunction with each other, and positions the seat piston <NUM> in the pilot closed position in the state where no electric current flows through the solenoid <NUM>. Moreover, the second coil spring <NUM> provides a biasing force acting in a closing direction from the open position to the closed position to the seat piston <NUM> via the main valve body <NUM> and positions the main valve body <NUM> in the closed position. Note that the second coil spring <NUM> can be replaced by a leaf spring, an elastic body, a magnetic spring, a pneumatic spring, a pressing mechanism that uses an electrostatic force, or the like.

The outer peripheral surface of the solenoid <NUM> is formed larger in diameter at the base end than at the remaining portion, and an annular channel <NUM> in the shape of a circular ring is formed between the remaining portion and the housing <NUM>. The annular channel <NUM> is connected to the second port <NUM> via the second channel <NUM>, is connected to the first port <NUM> via the gaps <NUM>, <NUM>, the communication channels <NUM>, <NUM>, and the first channel <NUM>, and forms a valve passage <NUM> together with these channels <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

In the gas solenoid valve <NUM> configured as described above, the spring housing chamber <NUM> is configured as follows. Specifically, the spring housing chamber <NUM> is formed by fitting the plunger <NUM> and the leading end portion 42b of the stationary pole <NUM> into the sleeve <NUM> and inserting the seat piston <NUM> through the leading end portion 41b of the plunger <NUM>; the spring housing chamber <NUM> is basically isolated from the other space. Meanwhile, a gap <NUM> is formed between the leading end portion 41b of the plunger <NUM> and the base end portion 14c of the seat piston <NUM>. The spring housing chamber <NUM> is connected to the valve passage <NUM> via this gap <NUM>, and gas is introduced into and discharged from the spring housing chamber <NUM> mainly via the gap <NUM> (refer to the arrow A in <FIG>). This gap <NUM> is formed so as to have a width S between <NUM> and <NUM>, inclusive, in order to limit the amount of gas to be introduced into and discharged from the spring housing chamber <NUM>. With this, abrupt changes in the volume of the spring housing chamber <NUM> are minimized, and the spring housing chamber <NUM> has a damping function, in other words, the spring housing chamber <NUM> plays the role of the damping chamber <NUM>.

Furthermore, a stopper <NUM> is provided on a leading end surface of the plunger <NUM>. The stopper <NUM> is formed in the approximate shape of a circular ring and protrudes from the leading end surface of the plunger <NUM> toward the main valve body <NUM>. When the main valve body <NUM> moves a predetermined distance L from the closed position in the opening direction, the stopper <NUM> configured as just described comes into contact with a base end surface of the main valve body <NUM>. Specifically, when the main valve body <NUM> moves the predetermined distance L, the stopper <NUM> limits the movement of the main valve body <NUM> (in other words, limits the amount of movement). With this, it is possible to minimize damage to the second coil spring <NUM> that occurs due to excessive stroke of the main valve body <NUM>.

The operation of the gas solenoid valve <NUM> will be described below. Specifically, as mentioned above, the gas solenoid valve <NUM> is provided on the gas tank and can cause the gas to flow in both directions in the valve passage <NUM> in order to fill the gas tank with the gas and discharge the gas from the gas tank, for example. For example, to cause the gas to flow from the second port <NUM> to the first port <NUM> as illustrated in <FIG>, an electric current flows to the coil 43b of the solenoid <NUM>. Therefore, the plunger <NUM> is lifted up, and the seat piston <NUM> moves to the pilot open position accordingly. Thus, the pilot passage 13d is opened, and the gas is guided to the first channel <NUM> through the two communication channels <NUM>, <NUM>, the slits 14b, 14b, and the pilot passage 13d. As a result, the difference in pressure between the gas in the valve chamber <NUM> and the gas flowing in the first channel <NUM> is reduced, and the main valve body <NUM> is eventually pushed up to the open position by the first coil spring <NUM>. Thus, the valve port <NUM> is opened, meaning that the valve passage <NUM> is opened, and the gas flows from the second port <NUM> to the first port <NUM> via the valve passage <NUM>. Subsequently, when the electric current stops flowing to the coil 43b, the second coil spring <NUM> pushes the main valve body <NUM> via the seat piston <NUM>, and the main valve body <NUM> moves to the closed position. Thus, the valve port <NUM> is closed, meaning that the valve passage <NUM> is closed, and the gas stops flowing.

On the other hand, to cause the gas to flow from the first port <NUM> to the second port <NUM> as illustrated in <FIG>, the gas solenoid valve <NUM> operates as follows. Specifically, when the gas flows from the first port <NUM> to the first channel <NUM>, the main valve body <NUM> is pushed in the opening direction by the pressure of the gas. Thus, the main valve body <NUM> moves to the open position, and the valve port <NUM> is opened, meaning that the valve passage <NUM> is opened. As a result, the gas flows mainly from the first channel <NUM> to each of the communication channels <NUM>, <NUM> through the valve port <NUM>, and is guided further to the second channel <NUM> through the gaps <NUM>, <NUM> and the annular channel <NUM>. The gas supplied to the first port <NUM> in this manner is guided to the second port <NUM> via the valve passage <NUM>. In the case where the valve passage <NUM> is opened as a result of the main valve body <NUM> being moved by the gas supplied to the first port <NUM> in this manner, the load acting on the main valve body <NUM> changes according to the degree of opening of the valve passage <NUM>, and thus the main valve body <NUM> vibrates, in other words, chattering occurs at the main valve body <NUM>. Regarding this issue, in the gas solenoid valve <NUM>, the occurrence of chattering at the main valve body <NUM> is minimized in the following manner.

Specifically, in the gas solenoid valve <NUM>, when the main valve body <NUM> is lifted up by the gas supplied to the first port <NUM>, the seat piston <NUM> is lifted up together. Accordingly, the seat piston <NUM> seated on the leading end portion 41b of the plunger <NUM> separates from the leading end portion 41b, and the damping chamber <NUM> is connected to the valve passage <NUM> via the gap <NUM> (refer to the arrow in <FIG>). In this manner, the gas is introduced into and discharged from the damping chamber <NUM> mainly via the gap <NUM>; as a result, abrupt changes in the volume of the damping chamber <NUM> are minimized while extension and retraction thereof are allowed, and thus vibrations of the seat piston <NUM> and the main valve body <NUM> can be damped. Therefore, it is possible to minimize the occurrence of chattering at the main valve body <NUM>.

Note that the main valve body <NUM> vibrates integrally with the seat piston <NUM>, and in some cases, the plunger <NUM>, and chattering occurs at the seat piston <NUM> and the plunger <NUM> as well. Regarding this, the damping chamber <NUM> minimizes the vibrations of not only the main valve body <NUM>, but also the seat piston <NUM> and the plunger <NUM> and thus can minimize the occurrence of chattering at these elements.

In the above-described manner, in the gas solenoid valve <NUM>, by supplying gas from the first port <NUM> to the first channel <NUM>, it is possible to open the valve port <NUM> and cause the gas to flow to the second port <NUM>, and at this time, the occurrence of chattering at the main valve body <NUM> can be minimized. Furthermore, by stopping the gas supply from the first port <NUM> to the first channel <NUM>, the main valve body <NUM> is pushed by the second coil spring <NUM> and moves to the closed position as in the case where the gas flows from the second port <NUM>. Thus, the valve port <NUM> is closed, meaning that the valve passage <NUM> is closed, and the gas stops flowing. In the gas solenoid valve <NUM>, it is possible to cause gas to flow from both the first port <NUM> and the second port <NUM> as described above.

In the gas solenoid valve <NUM> configured as described above, the spring housing chamber <NUM> is used as the damping chamber <NUM>, meaning that there is no need to form another damping chamber <NUM> to damp vibrations of the seat piston <NUM> and the main valve body <NUM>. Therefore, it is possible to avoid an increase in the size of the gas solenoid valve <NUM>. Furthermore, the amount of gas to be introduced into and discharged from the damping chamber <NUM> can be changed according to the width S of the gap <NUM>, and thus it is possible to adjust the damping force of the damping chamber <NUM> according to the width S of the gap <NUM>. Therefore, by adjusting the width S, it is possible to minimize the occurrence of chattering at the main valve body <NUM> and the seat piston <NUM> more effectively.

In the gas solenoid valve <NUM> according to the present embodiment, the spring housing chamber <NUM> is used as the damping chamber <NUM>, but does not necessarily need to be formed in such a manner in other unclaimed examples. For example, the housing space <NUM> may have the same function as the damping chamber <NUM>, or another damping chamber <NUM> may be formed separately. Furthermore, in the gas solenoid valve <NUM> according to the present embodiment, the amount of gas to be introduced into and discharged from the damping chamber <NUM> is adjusted according to the width S of the gap <NUM>, but the gas may be actively introduced into and discharged from the damping chamber <NUM> through the area between the sleeve <NUM> and the plunger <NUM>. In this case, by adjusting the distance between the leading end portion 42b of the stationary pole <NUM> and the plunger <NUM>, it is possible to adjust the amount of gas to be introduced and discharged, and the damping force of the damping chamber <NUM> can be adjusted accordingly.

Furthermore, instead of the gap <NUM>, a damping passage <NUM> may be formed as can be seen in an alternative unclaimed gas solenoid valve 1A illustrated in <FIG>. Specifically, the damping passage <NUM> is formed through the stationary pole <NUM> and the lid body <NUM> in order to connect the damping chamber <NUM> to the outside, and gas is introduced into and discharged from the damping chamber <NUM> through the damping passage <NUM>. Also in this case, by adjusting the diameter of the damping passage <NUM>, it is possible to adjust the amount of gas to be introduced and discharged, and the damping force of the damping chamber <NUM> can be adjusted accordingly. Note that the gas solenoid valve 1A has substantially the same configuration as the gas solenoid valve <NUM> except the damping passage <NUM>; in <FIG>, the same elements share the same reference signs. The same applies to a gas solenoid valve 1B to be described later. Furthermore, the damping passage may be formed in the seat piston <NUM>; in this case, the damping passage is formed so that the damping chamber <NUM> and the communication channels <NUM>, <NUM> are connected to each other through the damping passage.

In the gas solenoid valve <NUM> according to the present embodiment, the seat piston <NUM> is provided, but is not necessarily required in other unclaimed examples; the gas solenoid valve may instead be configured in such examples so that the plunger <NUM> is directly pressed against the main valve body <NUM>. Furthermore, as can be seen in a gas solenoid valve 1B illustrated in <FIG>, a seat piston 14B and a main valve body 13B may be configured to move in conjunction using a pin <NUM>.

Claim 1:
A gas solenoid valve, comprising:
a housing (<NUM>) including a first port (<NUM>), a second port (<NUM>), and a valve port (<NUM>) leading to the first port (<NUM>) and the second port (<NUM>);
a main valve body (<NUM>) capable of moving between a closed position and an open position and configured to move in an opening direction by pressure of gas supplied through the first port, the closed position being a position of the main valve body closing the valve port, the open position being a position of the main valve body opening the valve port;
a biasing member (<NUM>) that provides a biasing force to the main valve body to position the main valve body in the closed position, the biasing force acting in a closing direction from the open position to the closed position;
a seat piston (<NUM>) that is inserted through the main valve body, receives the biasing force of the biasing member, and biases the main valve body to the closed position; and
an electromagnetic drive device (<NUM>) that generates an excitation force to cause the main valve body to move to the open position, the excitation force opposing the biasing force of the biasing member, wherein:
a pilot passage (13d) connecting the first port and the second port is formed in the main valve body;
the seat piston is capable of moving between a pilot closed position and a pilot open position, the pilot closed position being a position of the seat piston closing the pilot passage, the pilot open position being a position of the seat piston opening the pilot passage;
the electromagnetic drive device includes a plunger (<NUM>) through which the seat piston is inserted in a manner to be movable in conjunction, a stationary pole (<NUM>) disposed facing the plunger, and a solenoid (<NUM>) that provides the excitation force to the plunger to attract the plunger to the stationary pole to cause the seat piston to move to the pilot open position and cause the main valve body to move to the open position;
a damping chamber (<NUM>) that damps movement of the main valve body is formed in the plunger to position the biasing member between the seat piston and the stationary pole;
the damping chamber is formed in a position located in the opening direction from the seat piston and adjacent to the seat piston;
the biasing member is disposed in the damping chamber; and
gas is introduced into and discharged from the damping chamber through a gap (<NUM>) between the seat piston and the plunger.