JPH053602U - Inertial body swing-back prevention valve - Google Patents

Abstract

(57) [Abstract] [Purpose] Only one is installed between the front and rear pipes of the fluid pressure actuator, and it works effectively for both forward and reverse motions of the actuator and inertial body. Provide an anti-sway valve. [Structure] One each before and after the actuator (two in total)
In addition to the structure of the conventional swing-back prevention valve that is installed, the shaft end 2 of the plunger 20 including the piston 30
3 and the plug 11 of the casing 10 communicate with the closed space to the second port B, and the diameter d of the piston 30
₁ and the diameter d ₂ of the seat surface 41 d ₂ = d ₁ / √2
To satisfy the relationship.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention is a valve that is mainly applied to hydraulic equipment for construction machines such as power shovels. Regarding things to prevent.

[0002]

[Prior Art]

 When moving an inertial body using a fluid pressure type actuator, it is needless to say that the fluid is supplied to the actuator from the supply side pipeline connected to a pump when driving, but when the actuator is stopped, the relief It is common to use a valve or the like to generate a limited amount of braking pressure in the return line from the actuator.

However, a so-called swing-back phenomenon occurs just before the inertial body stops. That is, when the inertial body is almost stopped and the braking pressure becomes equal to or less than the set value of the relief valve, 1) the inertial body is temporarily stopped by closing the relief valve, but in the return side pipeline. Since there is pressure energy corresponding to the pressure difference between the supply side pipeline and the energy, the actuator (and inertial body) begins to reverse. 2) At this time, the pressure in the return side pipeline rapidly increases. However, the pressure energy in the return line causes the actuator to reverse excessively (i.e., the return side pressure energy is replaced by the supply side pressure energy via the kinetic energy of the inertial body). Therefore, on the contrary, the pressure in the pipeline on the supply side increases, 3) the actuator further reverses based on the pressure energy on the supply side, and so on. Is done.

A device capable of preventing the above-described swing-back phenomenon even though it is a hydraulic device for moving an inertial body has already been described in Japanese Patent Publication No. 2-58481. The device of the publication has a circuit configuration shown in FIG. 3 (a). The hydraulic oil supply source 8 having a hydraulic pump 8a operates a directional control valve 8b (and a counterbalance valve 8c that switches simultaneously) to form a conduit 3A. Alternatively, by supplying hydraulic oil to 3B, the inertial body (not shown) is driven together with the hydraulic motor 2 in a desired direction. On the other hand, when the valve 8b (and the valve 8c) is set to the neutral position, the relief valve 4B or 4A causes a braking pressure to be generated in the return line 3B or 3A to stop the motor 2.

The device of FIG. 3 (a) is characterized in that it includes the swing-back prevention valve 101 of FIG. 3 (b), and the valve 101 is configured as follows. Explaining according to the drawings, the valve 101 has a casing 110 having a plug 111 attached to an end of a tubular portion, and a plunger 120, a piston 130, a seat member 140, a spring 150, a spring 160, and the like in an axial center. It is installed so that it can be moved along. Of these, the plunger 120 has a cylinder hole 121 and a small hole 122 connected to each other and penetrates through the inside thereof, and a pin-shaped piston 130 is slidably (slide) fitted inside the cylinder hole 121. The seat member 140 also has an inner hole 142 penetrating therethrough, and when the circumferential seat surface 141 comes into close contact with the shaft end portion of the plunger 120 on the small hole 122 side, the inner hole 142 becomes small. (And the cylinder hole 121). A spring 150 mounted between the plunger 120 and the casing 110 and a spring 160 between the seat member 140 and the casing 110 push the plunger 120 and the seat member 140 to the left in the figure, that is, toward the plug 111. Is installed as. The casing 110 containing these is a first port A ′ communicating with the shaft end of the seat member 140 on the right side (opposite side of the plunger) and its inner hole 142, and a second port B ′ communicating with the outside of the seat surface 141. Besides, the liquid chamber 115 is formed between the sheet member 140 and the sheet member 140. The liquid chamber 115 communicates with the first port A'through the orifice hole 116.

The swing-back prevention valve 101 is opened and closed as follows. First, when the pressure applied to the first port A ′ is high, a large force acts on the plunger 120 in the right direction (close to the seat member 140) in the figure based on the difference in cross-sectional area between the cylinder hole 121 and the seat surface 141. From this, the plunger 120 is pressed against the seat member 140, the seat surface 141 is brought into close contact, and the port A ′ and B ′ are closed. Further, when the pressure at the first port A ′ is low, the seat member 140 is pressed by the force of the spring 160 or the like against the plunger 120 moved toward the plug 11 1 by the force of the spring 150 or the like, so that the seat surface 141 After all, the port A'and B'is closed. However, when the pressure of the first port A ′, which was high until then, suddenly drops, the plunger 120 and the seat member 140 are separated from each other on the seat surface 141 until the state changes from the above state to the port A ′.・ B 'is opened. This is because, in this case, the seat member 140 is moved in the same direction by the damping action of the liquid chamber 115 having the orifice hole 116 with respect to the plunger 120 which is quickly moved to the plug 111 side by the force of the spring 150 or the like. This is because the transfer to is delayed.

In the apparatus shown in FIG. 3 (a), two such valves 101 are provided with the connection directions of the first port A'and the second port B'reversed with respect to the pipelines 3A and 3B before and after the motor 2. The swing back phenomenon of the motor 2 and the inertial body is effectively suppressed. As described above, this phenomenon is caused by the fact that the pressure energy is alternately increased in the pipe lines 3A and 3B before and after the motor 2 (supply side and return side), whereas the valve 101 is This is because, when the pressure at the port A'is about to drop, the ports A'and B ', that is, the two lines 3A and 3B are connected to quickly release the pressure energy. For example, when braking pressure is generated in the pipeline 3A to stop the motor 2, when the braking pressure approaches the stop and the braking pressure becomes less than or equal to the set value of the relief valve 4A, the valve 4A is first closed and the motor 2 is temporarily stopped. Immediately after that, the motor 2 starts reversing due to the pressure energy in the conduit 3A and the pressure in the conduit 3A is about to drop sharply. At that time, the valve 101 is connected between the conduits 3A and 3B. By communicating hydraulic fluid from the former side to the latter side, the pressure difference between the two approaches zero. The elimination of the pressure difference between the two pipelines 3A and 3B means that the pressure energy for reversing (that is, swinging back) the motor 2 is eliminated.

For further details regarding the structure and functions of the hydraulic system and valve 101 shown in FIG. 3, refer to the above-mentioned publication.

[0009]

[Problems to be solved by the device]

 In many cases, the direction in which the fluid pressure actuator drives the inertial body is bidirectional, that is, two directions, normal and reverse. This is true whether the actuator is, for example, a hydraulic motor or a hydraulic cylinder, and is generally applicable not only to construction machines but also to various machines.

However, the swing-back prevention valve 101 in FIG. 3B functions to open the ports A ′ and B ′ only when the pressure at the first port A ′ suddenly drops. In order to effectively prevent the swing-back at the time of stop in the bidirectional operation of 2 (and inertial body), as shown in FIG. Must be installed.

If two swing-back prevention valves are required in one device, the cost of the device is naturally high and the maintenance burden is also increased. In some cases, it may be difficult to secure a space for installing the valve in the device.

The object of the present invention is to install only one pipe between the front and rear pipes of the fluid pressure type actuator, and it is effective for both the bidirectional movement of the actuator and the inertial body. It is to provide a non-return valve.

[0013]

[Means for Solving the Problems]

In addition to the structure of the conventional valve described above (see FIG. 3 (b)), the inertial body swing-back prevention valve according to the present invention has a closed space between the shaft end of the plunger including the piston and the end of the casing. the causes communication with the second port, the diameter d ₂ of the diameter d ₁ and the seat surface of the piston was intended to satisfy the relationship d ₂ = d ₁ / √2 (i.e. ^{_{d 2 2 = d 1 2/}} 2).

[0014]

[Action]

 The action of the swing-back prevention valve of the present invention when the pressure is applied from the side of the first port is not particularly different from that of the conventional valve shown in FIG. 3 (b), and the above-mentioned explanations 1 to 3 are the same. This is true. The first and second ports are normally kept closed due to the close contact of the seat surface, and are opened only when the pressure (braking pressure) at the first port drops sharply from high pressure.

A feature of the swing-back prevention valve of the present invention is that the same action as described above is exerted on the pressure (braking pressure) from the second port. That is, since the closed space between the shaft end of the plunger including the piston and the end of the casing communicates with the second port, when the pressure applied to the second port is high, the plunger exerts a strong force on the seat. When pressed against the member, the seat surface comes into close contact, and the state between the first and second ports is closed.

When the pressure in the second port is low, the plunger is pushed toward the end of the casing (the side with the piston) by the force of the spring, etc., and the seat member is also pushed by the force of the spring and the small hole side of the plunger. Since the seat surface is pressed against the shaft end and the seat surface comes into close contact, the first and second ports are also closed.

However, when the pressure of the second port, which was high until then, suddenly drops, damping of the liquid chamber having an orifice hole is performed with respect to the plunger that moves promptly toward the end of the casing by the force of the spring or the like. Since the movement of the seat member in the same direction is delayed due to the action, the plunger and the seat member are separated from each other on the seat surface until the first port and the first port are opened, and Fluid flows from the port side to the first port side.

Moreover, the situation (opening) between the first and second ports (that is, the seat surfaces are separated) as described above is the same as that when the two ports are opened as described above. This is equal to the pressure in the second port (which is p _sb ) when is such that the pressure in the first port (which is p _sa ) is and in both cases both ports. The intervals are the same, and the reason is explained as follows.

The balance of the force exerted on the plunger at the moment when the high pressure applied to the first port suddenly drops and the plunger tries to separate from the seat member (that is, the above-mentioned state), If the force from the shaft end on the port or seat member side to the shaft end on the cylinder hole side is placed on the left side and the opposite force is placed on the right side, πd ₂ ² · p _sa / 4 + F = πd ₁ ² · p _sa / 4 (F is the magnitude of the force of the spring that acts on the plunger at the position of ·) On the other hand, the pressure at the second port drops sharply and the plunger separates from the seat member. ) balance the moment of the plunger from taking analogously left-right ^{_{F = πd 2 2 · p sb}} / 4 and d ₂ = d ₁ / √2 or more Type 3 according to the present invention, the p _sb = p _sa (See details such as the process by which the equation is derived. It referred in the Examples section).

Also, the time during which the first and second ports are open in and is nothing but the time until the seat member catches up with the plunger that has moved earlier, but that is because the fluid in the liquid chamber is It depends on the speed of exiting the orifice hole. Due to the fluid properties (viscosity, etc.), the orifice hole size, the force of the spring pushing the seat member, and the pressure difference between the inside and outside of the orifice, which are factors that affect the speed, the pressure acts on the first port side. There is no difference between the case where it is in the normal state and the case where it acts on the second port side. Therefore, in the case of, the time between both ports is the same as in the case of.

Therefore, if one port of the present invention is installed by connecting each of the first and second ports to each of the pipe lines before and after the fluid pressure type actuator (the reverse connection is also possible), Even when the actuator and the inertial body are operated in both directions, the swinging back at the time of stop is effectively prevented.

[0022]

【Example】

 FIG. 1 is a vertical sectional view of an anti-sway valve 1 according to an embodiment of the present invention. Further, FIG. 2 shows a hydraulic circuit using the valve 1 of FIG. 1 for driving the swing of a construction machine (power shovel). A supply source (not shown) similar to the hydraulic oil supply source 8 shown in FIG. 3A is connected to the lower portion of FIG. 2 (the portion following the pipe lines 3A and 3B). The swinging part of the machine, which is an inertial body, is driven in either direction by the hydraulic motor 2 of FIG. 2 capable of bidirectional rotation, and then the relief valve 4A or 4B (and the check valve 5A). If the braking pressure is generated and stopped by the action of 5B), the turning part and the motor 2 tend to swing back when stopping (the above-mentioned phenomenon), but this phenomenon is prevented. It is the role of this valve 1.

The structure of the valve 1 is not so different from that of the swing-back prevention valve 101 shown in FIG. That is, the plunger 20, the piston 30, the seat member 40, the spring 50, the spring 60, etc. are assembled inside the casing 10 along the axis. The explanation for each part is as follows.

Plunger 20: A cylinder hole 21 having an opening at one shaft end 23 (upper part of the drawing), and a small hole 22 having an opening at the other shaft end 24 continuing from the cylinder hole 21. . Each side surface near the shaft ends 23 and 24 is slidably held by the inner peripheral surface of the tubular portion of the casing 10. For the sake of explanation, the diameter of the latter sliding portion (outer diameter of the shaft end portion 24) is set to d ₃ .

Piston 30: A pin-shaped component that is slidably inserted into the cylinder hole 21 of the plunger 20 from its shaft end 23 so that the ends 31 and 32 are hemispherical. The length is slightly longer than the depth of the cylinder hole 21. The diameter of the piston 30 (substantially equal to the inner diameter of the cylinder hole 21) is d ₁ .

Seat member 40: A member arranged below the plunger 20 in the drawing so that the circumferential portion can closely contact with the shaft end 24 on the side of the small hole 22 of the plunger 20 as the seat surface 41. An inner hole 42 is provided over the entire length from the inside of the surface 41. Side surfaces of a portion near the sheet surface 41 and a flange portion 43 near the shaft end on the side opposite to the plunger (the side far from the seat surface 41) are held by the inner peripheral surface of the casing 10 in a sliding manner. ing. The diameter of the seat surface 41 is d ₂ .

Spring 50: It pushes the plunger 20 in the direction of the shaft end 23 on the cylinder hole 21 side, and is compressed and incorporated between the plunger 20 and the casing 10.

Spring 60: It is compressed and incorporated between the flange portion 43 of the seat member 40 and the casing 10 so as to push the seat member 40 toward the plunger 20. The spring force of this is weaker than that of the spring 50.

Casing 10: Has a cylindrical portion formed to hold the plunger 20 and the seat member 40 slidably in the axial direction, and the end portion (the upper end portion in the figure) is sealed with a plug 11. The end 31 of the piston 30 comes into contact with the plug 11. A first port A communicating with the shaft end of the seat member 40 on the side opposite to the plunger and the inner hole 42 is provided on the side opposite to the plug 11 (the lower end in the figure), and the passage 34 is provided on the side. The second port B communicates with the outer portion of the seat surface 41 and the mounting portion of the spring 50 via the. Further, in the portion of the casing 10 that slidably holds the sheet member 40, a liquid chamber 15 in which the hydraulic oil is sealed is provided between the flange portion 43 and the flange portion 43. However, the liquid chamber 15 communicates with the first port A via an orifice hole 16 on the side of the casing 10.

As shown in FIG. 2, the valve 1 is characterized in that, for one hydraulic motor 2 that rotates in both directions, only one hydraulic motor 2 is provided in the drive circuit, and the rotation of the motor 2 is stopped. It is to be able to prevent the shaking back at the verge. The following two points can be said to be the structure for that purpose.

The first point is that, as shown in FIG. 1, an axial notch groove is formed in a part of a side surface (a portion that slides with the casing 10) near the shaft end 23 of the plunger 20. Use the hydraulic oil communication passage 25. By forming the communication passage 25, a closed space that is sandwiched between the shaft end 23 of the plunger 20 including (the end 31 of) the piston 30 and the plug 11 of the casing 10 is provided as a second port B. Will be in communication with.

[0032] The second is that it has to satisfy the relation _{d 2 = d 1 / √2 ‥‥} (1) with the diameter d ₁ of the piston 30 and with the diameter d ₂ of the sheet member 40.

When the swing-back prevention valve 1 having such a configuration is used by connecting the first port A to the conduit 3A and the second port B to the other conduit 3B as shown in FIG. 2, for example, It works as follows.

When the pressure in the conduit 3A applied to the first port A is high: As described with reference to FIG. 1, the plunger 20 faces downward in the drawing based on the difference in cross-sectional area between the cylinder hole 21 and the seat surface 41 (the seat). Since the force acting on the member 40) is larger than the force in the opposite direction including the pressure from the second port B side and the force of the spring 50, the plunger 20 is pressed toward the seat member 40. Since the force of the spring 60 acts on the seat member 40, that is, the seat surface 41 is in close contact with the seat member 40 and the ports A and B are closed.

When the pressure of the pipe line 3A applied to the first port A is low: The force of the spring 50 and the force including the pressure from the second port B move the plunger 20 toward the plug 11, and the seat member against it. Since 40 is pressed by the force of the spring 60, the ports A and B are also closed on the seat surface 41.

When the pressure of the first port A suddenly drops from the above state: In this case, in the circuit of FIG. 2, the control pressure corresponding to the set value of the relief valve 4A is This occurs when the hydraulic motor 2 is braked in 3A and the hydraulic valve 2 is closed soon before the relief valve 4A is closed, and the motor 2 begins to reverse (sway back) due to the pressure energy in the conduit 3A. In this case, in the valve 1, since the movement of the seat member 40 is delayed by the damping action of the liquid chamber 15 having the orifice hole 16, the movement of the seat member 40 is delayed with respect to the plunger 20 which is quickly moved to the plug 11 side by the force of the spring 50. At 41, the plunger 20 and the seat member 40 are separated, and the ports A and B are opened. Therefore, the hydraulic oil in the conduit 3A flows through the valve 1 into the conduit 3B, and the pressure energy that causes reversal disappears in a short time.

At the moment when the seat surface 41 is about to open as the pressure of the first port A decreases from the above state, the balance of the force applied to the plunger 20 is from the shaft end 24 near the seat member 40. If a force (upward in the figure) toward the shaft end 23 on the cylinder hole 21 side is set on the left side and a force in the opposite direction is set on the right side, then πd ₂ ² · p _sa / 4 + F = πd ₁ ² · p _sa / 4 (2) (p _sa is the pressure of the first port A at the moment the seat surface 41 opens at. F is the moment, that is, the force of the spring 50 acting on the plunger 20 in the still position. ), And F = π (d ₁ ² −d ₂ ² ) · p _sa / 4 (2 ′) is derived from this.

(Conversely to the above) When the pressure in the conduit 3B applied to the second port B is high: The pressure in the second port B passes through the passage 34 and the communication passage 25 and the end portion 31 of the piston 30 and the plunger. Since it also acts on the shaft end portion 23 of 20, the plunger 20 is pressed toward the seat member 40 by a strong downward force exceeding the force of the spring 50 including the pressure from the first port A side. Further, since the force of the spring 60 acts on the seat member 40, the seat surface 41 is in close contact with the seat member 41 and the ports A and B are closed.

When the pressure of the conduit 3B applied to the second port B is low: The force of the spring 50 and the force including the pressure from the first port A move the plunger 20 toward the plug 11, and the seat member Since 40 is pressed by the force of the spring 60, the ports A and B are also closed on the seat surface 41.

When the pressure of the second port B suddenly drops from the above state: In this case, contrary to the above in FIG. 2, the braking pressure corresponding to the set value of the relief valve 4B Occurs in the pipeline 3B to brake the hydraulic motor 2, and soon after the relief valve 4B is closed, the motor 2 begins to reverse (sway back) due to the pressure energy in the pipeline 3B. In the valve 1, similarly to the above case, the movement of the seat member 40 is delayed with respect to the plunger 20 that quickly moves to the side of the plug 11, so the plunger 20 and the seat member 40 are separated by the seat surface 41 and the port A The space between B opens. This time when ports A and B are open is no different from the time in the above case. The time is nothing but the time until the seat member 40 catches up with the previously moved plunger 20, and is determined by the speed at which the hydraulic oil in the liquid chamber 15 flows out from the orifice hole 16, but is the same as Since the hydraulic fluid flows through the same orifice hole 16 and flows out under the same condition that there is no difference in pressure inside and outside the same hole 16 under the force of the same spring 60, it naturally coincides with the time. During this period, the hydraulic oil in the conduit 3B flows through the valve 1 into the conduit 3A, so that the pressure energy that causes the reversal disappears.

Similar to the above, consider the balance of the force of the plunger 20 at the moment when the seat surface 41 is about to open as in the state of (from the shaft end 24 toward the shaft end 23). Force on the left side and the opposite force on the right side) and π (d ₃ ² −d ₂ ² ) p _sb / 4 + F = πd ₃ ² · p _sb / 4 (3) (p _sb is the pressure of the second port B at the moment when the seat surface 41 is opened at, and F is the force of the spring 50 acting on the plunger 20 at that moment, that is, the position F, which is expressed by the above formula (1). The same size)), and F = πd ₂ ² · p _sb / 4 (3 ′) is derived from this.

When F is deleted from equations (2 ′) and (3 ′), πd₂ ²・ P_sb/ 4 = π (d₁ ²-D₂ ²) ・ P_sa/ 4 ∴p_sb = P_saX (d₁ ²-D₂ ²) / D₂ ²  However, in this valve 1, since the above equation (1) holds, d₂ ²= D₁ ²Substituting / 2 into the above equation yields p_sb = P_sa  That is, the pressure at the second port B at the moment when the seat surface 41 is opened becomes equal to the pressure at the first port A at that moment. This means that, in the circuit of FIG. 2, the pressure condition in which the valve 1 starts to open after the braking pressure is applied to the side of the conduit 3B is that the motor 2 rotates in the opposite direction to that of the conduit 3A side when stopped. This means that the pressure condition is the same as the condition that valve 1 starts to open after the braking pressure is applied to.

As described above, since the time during which the ports A and B are open is the same, the function of the valve 1 to prevent the motor 2 (and the inertial body that is its load) from swinging back is The same effect can be obtained in both rotation directions.

Although one embodiment has been introduced above, the swing-back prevention valve of the present invention can also be implemented as follows. That is, (a) It is easy to stabilize the axial movement of each component by slidably holding the plunger and the seat member on each of the plurality of side surfaces by the casing, but it is not always essential. Therefore, for example, in FIG. 1, a part of the casing 10 holding the side surface (portion having the diameter d ₃ ) near the shaft end 24 of the plunger 20 may be cut off as indicated by an imaginary line x in the drawing. . Excising this portion facilitates formation of the passage 34. In that case, although the above equation (3) is a little strange, the equation (3 ′) is directly derived instead.

(B) It goes without saying that the valve of the present invention can be used in circuits other than that shown in FIG. For example, the relief valve can be used in the circuit shown in Fig. 3 (a) with different connection method (of course, the original two valves 101 are removed and one valve of the present invention is connected). It can also be used in other circuits that use hydraulic cylinders as actuators.

C) Even if the actuator is operated only in one direction, it may be used. Since the valve of the present invention has no parts that are more difficult to manufacture than the conventional valve (see FIG. 3 (b)), there is no cost demerit in that case.

D) Although all the plungers and piston / seat members have been described as having a circular cross section, they do not have to be circular in principle. This is because when the cross section is rectangular or hexagonal (which is not advantageous in manufacturing), the same action and effect as in the case of the circular shape are obtained. In that case, however, the diameter of each part described in the claims should be read as an appropriate cross-sectional dimension (side length, side-to-side dimension, etc.), or the relational expression should be replaced with the relational expression between cross-sectional areas as necessary. Should be.

[0048]

[Effect of the device]

 The anti-sway return valve of the present invention is installed only between the front and rear pipe lines of the fluid pressure type actuator, and is equivalent to the forward and reverse motions of the actuator and the inertial body. Prevent them from rolling back when stopped. Compared with the conventional anti-sway valve that required two before and after the same actuator, there is no part that is difficult to manufacture and there is no increase in size, so cost, installation space, and maintenance are remarkably high. It is advantageous.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a swing-back prevention valve 1 according to an embodiment of the present invention.

FIG. 2 is a hydraulic circuit diagram showing an example of an apparatus using the valve 1 of FIG.

FIG. 3 (a) is a hydraulic circuit diagram of an apparatus using a conventional swing-back prevention valve, and FIG. 3 (b) is a vertical cross-sectional view showing the conventional swing-back prevention valve.

[Explanation of symbols]

 10 Casing 11 Plug (End) 15 Liquid Chamber 16 Orifice Hole A First Port B Second Port 20 Plunger 21 Cylinder Hole 22 Small Hole 25 Communication Passage 30 Piston 40 Seat Member 41 Seat Surface 42 Inner Hole 50/60 Spring

Claims (1)

[Claims for utility model registration] [Claim 1] In order to prevent the inertial body, which is the load of the fluid pressure type actuator, from swinging back when stopped, a) a cylinder hole with an opening at one shaft end and its A plunger having a small hole continuing from the cylinder hole and having an opening at the other shaft end, b) having a diameter d _{1 which} is slidably fitted into the cylinder hole of the plunger through the shaft end. A piston, c) a seat member having a diameter d ₂ circumferential portion which can closely contact as a seat surface with the small hole side shaft end of the plunger, and which has an inner hole connected to the small hole over the entire length from the inside of the seat surface, d) a spring that pushes the plunger toward the shaft end on the cylinder hole side, and e) a spring that pushes the seat member toward the plunger. Or b) having a first port communicating with the shaft end of the seat member on the side opposite to the plunger and its inner hole, and a second port communicating with the outside of the seat surface. ) A valve constructed by incorporating a liquid chamber communicating with a first port through an orifice hole between a seat member and a casing, the shaft end of the plunger including a piston and the end of the casing. The inertial body swings back, characterized in that the closed space between and is communicated with the second port, and the relationship of d ₂ = d ₁ / √2 is satisfied for the diameters d ₁ and d ₂ described above. Prevention valve.