JPH0459505B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a relief valve that suppresses the internal pressure of a cryogenic cryogen container used in a nuclear magnetic resonance imaging apparatus or the like to a predetermined value or less.

B. Prior Art A nuclear magnetic resonance imaging device has a cryogenic cryogen container filled with a cryogenic cryogen such as liquid helium, and a superconducting magnet having a coil made of niobium titanium or the like is immersed in the cryogen container to generate a high magnetic field. This allows a cross-sectional photograph of the human body to be obtained. In this type of device, when the superconductivity is broken (this is called quenching) and resistance is generated in a part of the coil, it generates heat and evaporates liquid helium, and the evaporated gas increases the pressure inside the cryogenic container and destroys the container. There is a risk of

Therefore, conventionally, as shown in FIG.
and a leak valve 3 consisting of a fixed throttle or a manual needle valve, thereby releasing the pressure inside the container to the outside. That is, a small amount of gas generated by normal heat penetration is released from the leak valve 3, and the relief valve 2 is provided with a metal thin film 2a made of a non-magnetic material such as aluminum that blocks the upper and lower parts of the pipe line 1. When the pressure inside the container reaches a predetermined value, the metal thin film 2a is broken and communicated with the upper and lower portions of the pipe 1, and as a result, the evaporated gas inside the container is discharged to the outside and the pressure inside the container is suppressed. .

C Problems to be Solved by the Invention However, with the leak valve 3 described above, when the flow rate of released gas becomes extremely small due to fluctuations in outside pressure, moisture may enter from the outside and cause freezing, and the relief valve 2, the metal thin film 2a
If one is destroyed, it must be replaced with a new one each time, resulting in poor work efficiency. Furthermore, after the metal thin film 2a is destroyed, even if the internal pressure of the cryogen container returns to its normal value, evaporated gas is undesirably discharged, and outside air flows through the pipe 1 into the cryogen container. There is a risk that the refrigerant will flow back and accelerate the evaporation of the refrigerant.
Furthermore, although it may temporarily go into a quench state and return to a superconducting state, once the quench occurs, the thin metal film 2a will be destroyed, and once the superconducting state returns, the operation must be stopped. ,ineffective.

SUMMARY OF THE INVENTION An object of the present invention is to provide a relief valve for protecting cryogen containers that solves the above-mentioned problems.

D Means for Solving the Problems The present invention is implemented in a relief valve for protecting a cryogenic cryogen container that is provided in a communication path between a cryogenic cryogen container in which a cryogenic cryogen is sealed and the outside. The problem described above is that the valve body includes a thin film that is displaced between the open position and the closed position and closes the communication passage in the closed position, and that the valve body remains closed until the pressure inside the container reaches a first predetermined value. an elastic body that biases the valve to the closed position, and when the pressure exceeds a first predetermined value, the valve body overcomes the force of the elastic body and floats to open the passage in accordance with the pressure, and further the pressure reaches the first predetermined value. When a second, larger predetermined value is reached, the problem is solved by breaking the membrane and opening the communication path.

E Effect The valve body is biased to the closed position by the elastic body until the pressure inside the container reaches the first predetermined value, and when the pressure inside the container reaches the first predetermined value, it is displaced to the open position. The evaporated gas inside the low-temperature cryogen container is discharged to the outside, and the pressure inside the container is suppressed. In addition, if the valve body becomes inoperable due to freezing of the elastic body, and the pressure inside the container reaches a second predetermined value, the thin film that makes up the valve body breaks and opens the communication passage, which causes the inside of the container to The evaporated gas is discharged to the outside and the pressure inside the container is suppressed.

F Example One example of the present invention will be described based on FIG.

() Structure of the Embodiment FIG. 1 is a front sectional view showing a case where the relief valve for a cryogen container according to the present invention is implemented in a nuclear magnetic resonance imaging apparatus.

A cryogenic cryogen container 12 is provided inside the vacuum container 11 of the nuclear magnetic resonance imaging apparatus 10, and a superconducting magnet (not shown) is placed in liquid helium (cryogenic cryogen) sealed in the cryogenic cryogen container 12. immersed. The vacuum container 11 is a cryogenic cryogen container 1
The space 13 defined by the vacuum container 11 and the cryogenic cryogen container 12 is a vacuum. Reference numeral 21 denotes a conduit (communication path) that communicates the cryogenic cryogen container 11 with the outside, and a relief valve 30 is provided at the tip of this conduit 21 .

This relief valve 30 will be explained below.

A flange 31 is attached to the circumferential surface of the tip of the conduit 21, and an outer cylinder 32 and an inner cylinder 33 are provided on the upper surface of the flange 31 so as to be concentric with the conduit 21.
The outer cylinder 32 is screwed onto the flange 31 via the flange 32a, and the inside of the outer cylinder 32 and the outside of the cylinder are sealed with an O-ring 41. Inside the inner cylinder 33, a valve element 34, which is formed by sandwiching a metal thin film 34c between a pair of annular disks 34a and 34b, is provided so as to be slidable between an open position and a closed position.
The inside of 3 and the outside of the cylinder are sealed with an O-ring 42.

The valve body 34 is pressed against the flange 31 by a spring 35 and urged to the normally open position, so that the metal thin film 34
c closes the outlet of the conduit 21. The spring receiver 36 that holds the other end of the spring 35 is connected to the inner cylinder 3
The spring force of the spring 35, that is, the relief pressure (e.g., 0.1 Kg/cm ² G, first predetermined value) is adjusted by advancing and retreating the adjusting screw 37. It is possible. In addition, as the above-mentioned metal thin film 34c,
Non-magnetic materials such as aluminum, stainless steel or copper are used.

In addition, a communication hole 33a is provided in the side wall of the inner cylinder 33.
A communication hole 33b is opened on the top surface, and a chamber 38 between the outer cylinder 32 and the inner cylinder 33 is communicated with the inside of the inner cylinder 33. Furthermore, the upper end of the outer cylinder 32 is opened and connected to the pipe line (communication path) 22,
It is communicated with the outside of the installation room of the nuclear magnetic resonance imaging apparatus 10 via.

() Operation of the Embodiment When a small amount of heat enters from the outside of the cryogenic cryogen container 12 due to radiation or the like, a small flow rate of gas is generated depending on the amount of heat. In addition, cryogenic cryogen container 1
When the superconducting state of the superconducting magnet immersed in liquid helium in the coil is broken and resistance is generated in the coil, heat is generated and the liquid helium rapidly evaporates. When the internal pressure of the container 12 rises due to the evaporated gas and overcomes the biasing force of the spring 35, the valve body 34 is displaced to the open position, and the evaporated gas of the liquid helium in the container 12 is transferred to the pipe line 21, the inner cylinder 33, communication hole 33a
After being guided into the chamber 38, it passes through the conduit 22 and is discharged to the outside. When the internal pressure of the container 12 decreases due to the evaporative gas being discharged to the outside, the valve body 34 is displaced to the closed position by the biasing force of the spring 35, and the pipe line 21 and the chamber 38 are cut off.

Furthermore, if the disc 34a, O-ring 42, spring 35, etc. freeze due to the influence of liquid helium, which is a cryogenic cryogen, the opening/closing movement is hindered and the valve body 34 becomes inoperable. As a result, the internal pressure of the container 12 increases to a predetermined value (for example, 0.7 Kg/cm ² G, a second predetermined value) that is higher than the relief pressure set by the spring 35.
When the temperature reaches this point, the metal thin film 34c is destroyed and the evaporated gas is similarly discharged to the outside through the pipe 22.

As described above, when the pressure inside the cryogenic cryogen container 12 reaches the predetermined relief pressure, the valve body 34
is displaced to the open position, the evaporated gas in the container 12 is discharged to the outside, and when the pressure in the container 12 falls below this relief pressure, the valve body 34 is displaced to the closed position by the biasing force of the spring 35. Therefore,
Unlike conventional relief valves, there is no need to replace the membrane each time evaporative gas is discharged. Further, when the pressure inside the container 12 falls below a predetermined value, undesirable evaporative gas is prevented from being discharged, and outside air is also prevented from entering into the container 12 and accelerating the evaporation of liquid helium. . Furthermore, if the valve body 34 does not operate due to freezing of the spring 35, etc., the metal thin film 34c is destroyed and the pipes 21 and 22 are communicated with each other, which allows sufficient discharge of evaporated gas, thereby increasing safety. improves.

G Effect of the Invention Since the present invention is constructed as described above, when the pressure inside the container reaches the first predetermined value, the valve body opens and the evaporated gas in the cryogenic refrigerant container is discharged to the outside. The pressure inside the container can be suppressed without replacing the thin film, thereby improving work efficiency. In addition, the valve body closes after the pressure inside the cryogen container returns to a steady value, thereby preventing undesired discharge of evaporated gas, and
Acceleration of evaporation of cryogenic cryogen due to backflow of outside air is prevented. Therefore, wasteful leakage of expensive liquid helium is prevented. In addition, even if the valve body does not operate due to freezing of the elastic body, for example, when the pressure inside the container reaches a second predetermined value, the thin film that makes up the valve body breaks and the evaporated gas flows out, thereby ensuring safety. You can improve your sexual performance.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view showing an embodiment of a relief valve for protecting a cryogen container according to the present invention. FIG. 2 is a diagram showing a conventional example corresponding to FIG. 1. 10: Nuclear magnetic resonance imaging device, 12: Cryogenic cryogen container, 21, 22: Pipe line, 30: Relief valve, 3
4: Valve body, 34a, 34b: Annular disk, 34c:
Metal thin film, 35: Spring.

Claims (1)

[Claims] 1. A cryogenic cryogen container protection relief valve provided in a communication passage between a cryogenic cryogen container filled with cryogenic cryogen and the outside, which is displaced between an open position and a closed position, and in the closed position, the said communication passage is closed. The valve body includes a valve body including a thin film that closes, and an elastic body that biases the valve body to a closed position until the pressure inside the container reaches a first predetermined value, and when the pressure inside the container reaches the first predetermined value or more, the elastic body biases the valve body to a closed position. The valve body overcomes the force of the body and floats to open the passage in accordance with the pressure. When the pressure reaches a second predetermined value that is greater than the first predetermined value, the thin film breaks and the connection opens. A relief valve for protecting cryogen containers characterized by opening a passage.