Burst disc arrangement and a method for replacing a burst disc in a burst disc arrangement

1. A burst disc arrangement for a cryostat comprising a replaceable burst disc ( 52 ) held in compression between a high-pressure flange ( 60 ) formed at an end of a high-pressure conduit ( 12 ), and a low-pressure flange ( 60 ) formed at an end of a low-pressure conduit ( 14 ),

characterised in that:

the burst disc arrangement further comprises:

a housing ( 50 ) enclosing the high- and low-pressure flanges ( 60 ), said housing ( 50 ) including a first opening ( 20 ) large enough to allow the replaceable burst disc ( 52 ) to pass therethrough; and

compression means ( 56 ), distributed around the housing ( 50 ) and being arranged to bear upon at least one of the flanges ( 60 ), so as to urge it towards the other of the flanges, thereby retaining the burst disc ( 52 ) in compression between the low- and high-pressure flanges ( 60 ).

2. A burst disc arrangement according claim 1 , wherein a sensor ( 54 ) is provided, adjacent to the burst disc, to provide an indication of the state of the burst disc.

3. A burst disc arrangement according to claim 1 wherein the housing ( 50 ) accommodates the flanges ( 60 ), the burst disc ( 52 ) and any sensor ( 54 ) within a cavity ( 51 ) shaped and dimensioned so as to accommodate the flanges ( 60 ), the burst disc ( 52 ), optionally also sensor ( 54 ), with a sufficient axial clearance ( 53 ) to allow the insertion and removal of a burst disc ( 52 ), optionally also a sensor ( 54 ).

4. A burst disc arrangement according to claim 3 wherein an axial dimension of the cavity ( 51 ) is greater than the sum of the axial dimensions of the flanges ( 60 ), the burst disc ( 52 ) and any sensor ( 54 ) by an amount sufficient to provide clearance ( 53 ) to enable the insertion and removal of burst disc ( 52 ) and optionally also sensor ( 54 ); and a diameter of the cavity ( 51 ) is greater than the diameters of each of the flanges ( 60 ), the burst disc ( 52 ) and any sensor ( 54 ) by an amount sufficient to provide clearance ( 55 ) to enable axial movement of flanges ( 60 ), the burst disc ( 52 ) and any sensor ( 54 ) within the cavity ( 51 ).

5. A burst disc arrangement according to claim 1 , wherein the compression means comprises sealing bolts ( 56 ) in threaded through-holes spaced at intervals around the housing ( 50 ).

6. A burst disc arrangement according to claim 1 , wherein the housing ( 50 ) includes a second opening ( 64 ), smaller than the first opening, placed diametrically opposite a part of the first opening ( 20 ), allowing limited access to a surface of the burst disc.

7. A burst disc arrangement according to claim 1 , wherein the housing ( 50 ) is of two parts, respectively placed over the high- and low-pressure flanges ( 60 ) and joined together.

8. A burst disc arrangement according to claim 1 , wherein the burst disc ( 52 ) is provided with a gasket seal on at least one face, in contact with a corresponding at least one of the low- and high-pressure flanges.

9. A method for replacing a burst disc in a burst disc arrangement according to claim 1 , comprising the steps of:

loosening the compression means ( 56 ) sufficiently to relieve pressure on the burst disc ( 52 ), and allow sufficient clearance for the burst disc to be removed and replaced through the opening ( 20 );

extracting the burst disc ( 52 ) from between the high- and low-pressure flanges and through the opening ( 20 );

inserting a replacement burst disc ( 52 ) through the opening ( 20 ) and between the high- and low-pressure flanges; and

re-tightening the compression means.

10. A method according to claim 9 wherein the compression means comprises sealing bolts ( 56 ) in threaded through-holes spaced at intervals around the housing ( 50 ), and the sealing bolts ( 56 ) and housing ( 50 ) being suitably dimensioned that the burst disc may be removed and replaced without requiring the bolts to be completely removed from their thread.

11. A burst disc arrangement according to claim 2 , wherein the sensor ( 54 ) is arranged to detect the bursting of a burst disc, indicating the opening of an exit path from a cryostat fitted with a cryogenic refrigerator operated by a compressor ( 68 ), arranged to stop operation of the compressor in response to such detection.

12. A burst disc arrangement according to claim 11 , wherein the sensor ( 54 ) is of similar size to the burst disc, placed between the burst disc and one of the high- and low-pressure flanges, said sensor being removable and replaceable by a method comprising the steps of:

loosening the compression means ( 56 ) sufficiently to relieve pressure on the sensor ( 54 ), and to allow sufficient clearance for the sensor to be removed and replaced through the opening ( 20 );

extracting the sensor ( 54 ) from between the high- and low-pressure flanges and through the opening ( 20 );

inserting a replacement sensor ( 54 ) through the opening ( 20 ) and between the high- and low-pressure flanges; and

re-tightening the compression means.

13. A burst disc arrangement according to claim 11 , wherein the sensor ( 54 ) provides on/off functionality, and which sensor is in a first state on installation, but which changes to a second, opposite, state in response to the bursting of the burst disc ( 52 ).

14. A burst disc arrangement according to claim 11 wherein the sensor is arranged to be linked to an alarm system for indicating the rupture of the burst disc to a user or a service organisation.

15. A burst disc arrangement according to claim 12 , wherein the sensor ( 54 ) provides on/off functionality, and which sensor is in a first state on installation, but which changes to a second, opposite, state in response to the bursting of the burst disc ( 52 ).

16. A burst disc arrangement according to claim 12 wherein the sensor is arranged to be linked to an alarm system for indicating the rupture of the burst disc to a user or a service organisation.

17. A burst disc arrangement according to claim 13 wherein the sensor is arranged to be linked to an alarm system for indicating the rupture of the burst disc to a user or a service organisation.