A PRESSURE LIMITING VALVE FOR A CRYOSTAT CONTAINING A CRYOGEN AND A SUPERCONDUCTING MAGNET

Abstract

An abstract for a quench valve of a cryostat, in particular for use in a magnetic resonance imaging system, is attachable to the quench valve so as to raise the cracking pressure of the quench valve without changing the operability of the quench valve. Such an accessory device is usable to enable the cryostat, containing a cryogen, to be safely transported by air transportation.

Claims

1. A pressure limiting valve for a cryostat containing a cryogen and a superconducting magnet, the pressure limiting valve comprising: a quench valve allowing cryogen gas to exit the cryostat upon occurrence of a quench of the superconducting magnet; a cracking-pressure-raising accessory removably attached to the quench valve; wherein the quench valve comprises comprising a valve plate and a valve seat and a first spring arrangement that urges the valve plate against the valve seat; and the accessory comprising a main body detachably mounted on the quench valve or the cryostat, and further comprising a second spring arrangement having a number of second spring elements directly or indirectly acting upon the valve plate and further urging said valve plate against said valve seat, said main body providing a counter bearing for the second spring arrangement.

2. The pressure limiting valve as claimed in claim 1, wherein the accessory further comprises at least one plunger, said at least one plunger directly or indirectly acting upon the valve plate, said at least one plunger being spring-loaded by at least one of said number of second spring elements.

3. The pressure limiting valve as claimed in claim 2, wherein the main body of the accessory device forms an enclosure for at least one of the second spring elements and the first spring arrangement.

4. The pressure limiting valve as claimed in claim 1, wherein the main body of the accessory device comprises a number of openings forming vent holes.

5. A method of enabling a cryostat containing a cryogen and a superconducting magnet to be safely transported by air transportation, said cryostat comprising a quench valve allowing cryogen gas to exit the cryostat upon occurrence of a quench of the superconducting magnet, wherein the quench valve comprises a valve plate urged against a valve seat by a first spring arrangement, the method comprising: prior to air transportation, removably attaching a cracking-pressure-raising accessory to the quench valve, wherein the accessory comprises a main body detachably mounted on the quench valve or the cryostat, and further comprises a second spring arrangement having a number of second spring elements directly or indirectly acting upon the valve plate and further urging said valve plate against said valve seat, said main body providing a counter bearing for the second spring arrangement.

6. a quench valve of a cryostat containing a cryogen and a superconducting magnet, as pressure-relief device for subsequent in case of air transportation of said cryostat, wherein the quench valve comprises a valve plate urged against a valve seat by a first spring arrangement, to which quench valve a cracking-pressure-raising accessory device has been installed prior to air transportation, the accessory comprising a main body detachably mounted on arrangement having a number of second spring elements directly or indirectly acting upon the valve plate and further urging said valve plate against said valve seat, said main body providing a counter bearing for the second spring arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows a schematic illustration of a cryostat (prior art).

[0014] FIG. 2 shows a schematic illustration of a quench valve of the cryostat in a sectional view (prior art).

[0015] FIG. 3 shows a schematic illustration of a quench valve of the cryostat, according to the present invention, in a sectional view.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A cross-section of a superconducting magnet system for use in an MRI system is illustrated in FIG. 1. Superconductive magnet coils (not shown) are provided in a cryogen vessel 2 of a cryostat 1. The coils are immersed in a liquid cryogen 3, e.g. liquid helium. A central bore 4 is provided to accommodate a patient for examination. An access neck 5 with vent tube 6 is provided at the top of the cryostat 1 to allow access to the cryogen vessel 2. For clarity reasons, other parts of the cryostat 1, e.g. the refrigerator for providing active refrigeration to cool the cryogen 3, the outer vacuum chamber, or the thermal radiation shields, are not shown.

[0017] As illustrated in FIG. 2 in more detail, a turret outer assembly 7 encloses upper extremities of the access neck 5, and provides a normal exit path for cryogen gas from cryogen vessel 2. Turret outer assembly 7 is joined to the cryogen vessel 2 in a leak-tight manner and defines an interior volume which is separated from atmosphere by a protective valve and/or burst disc, in this case by a quench valve 8. The quench valve 8 is closed until a certain pressure is reached within the cryogen vessel 2. Once the cryostat pressure reaches the certain value, the quench valve 8 is opened by the pressure acting upon it.

[0018] Quench valve 8 includes a valve plate 9 which is held against valve seat 10 by a first spring arrangement 11. In case of overpressure within cryogen vessel 2, a corresponding pressure of cryogen gas acting on the inner side 12 of the valve plate 9 will exceed the pressure acting on the outer side 13 of the valve plate 9 sufficiently to overcome the force of the first spring arrangement 11 and open the quench valve 8. Cryogen gas will escape, maintaining the pressure within the cryogen vessel 2 at an acceptable level. Once the pressure in the cryogen vessel 2 drops below the pressure needed to keep the quench valve 8 open, first spring arrangement 11 will press the valve plate 9 back into contact with valve seat 10. Part of the valve plate 9 may be formed by a burst disc, not visible in FIG. 2 as it lies in the plane of the valve plate 9. In case the differential pressure across the valve plate 9 becomes much higher than the pressure at which the quench valve 8 should open, for example if the quench valve 8 sticks, or the pressure increase within the cryogen vessel 2 is extremely rapid or severe, the burst disc will rupture and cryogen gas will then escape through a hole left by the burst disc and out of the cryogen vessel 2. This burst disc is typically a declared regulatory pressure relief safety device, provided to rupture in the event of quench valve failure.

[0019] An embodiment of the invention is depicted in FIG. 3. The existing quench valve 8, as shown in FIG. 2, is modified prior to air shipment, without thereby loosing the valve operability of the quench valve 8. During modifying no part is removed from the quench valve 8. Instead, an accessory device 14 is installed to the quench valve 8, which temporarily raises the cracking pressure of the quench valve 8.

[0020] The accessory device 14 comprises a main body 15 forming a cylindrical or box-shaped container 16 with walls 17, with an open front 18 and a back plate 19. The main body 15 is provided with a number of small vent holes, which serve as openings to allow cryogen gas originating from the quench valve 8 to escape from the container 16 in case of a quench. An exemplary position of the vent holes is indicated in FIG. 3 by arrow 20. The main body 15 is fitted to the outer flange 21 of the quench valve 8 by means of removable fastening elements 22, e.g. screws. For this purpose, the front end of the main body 15 is extended to form mounting flanges 23.

[0021] The back plate 19 is arranged parallel to the valve plate 9 of the quench valve 8, when the accessory devices 14 is mounted. A second spring arrangement 24 comprising four spring-loaded plungers 25 is provided within the container 16. In FIG. 3 only two plungers 25 are illustrated. The plungers 25 bear on the valve plate 9, by this means raising the cracking pressure of the quench valve 8. The second spring arrangement 24 comprises four spring elements 26 in the form of compression springs. The spring elements 26 are employed to act on the plungers 25, in order to provide the spring load, as required. The back plate 19 of the main body 15 acts as counter bearing for the spring elements 26. For each spring element 26 an internal guiding rod 27 is provided. All guiding rods 27 are mounted to the back plate 19 of the main body 15.

[0022] By means of the accessory device 14, using the second spring arrangement 24, the cracking pressure of quench valve 8 may be raised for example from 6 to 13 PSIG. In case of overpressure during air shipment, the pressure of cryogen gas acting on the inner side 12 of the valve plate 9 has to overcome the force of the second spring arrangement 24 in order to open the quench valve 8. In this event, cryogen gas exits the cryogen vessel 2 and enters the container 16, from which the gas escapes through the number of small vent holes.

[0023] When mounted, the main body 15 of the accessory device 14 is adapted to serve as a protective enclosure both for the first and second spring arrangement 11, 24, as well as for the surroundings of the cryogen vessel 2 in case of a rupture of a burst disc.

[0024] On arrival in the hospital or any other operational site, the accessory device 14 is removed, bringing the quench valve 8 back into its normal operation mode.

[0025] Although modifications and changes may be suggested by those skilled in the art, it is the intention of the Applicant to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of the Applicant's contribution to the art.