Pressure relief valve for cryogenic vessel

1 . A pressure relief valve for a cryogenic vessel, the pressure relief valve comprising:

valve walls defining a fluid flow passageway through the pressure relief valve;

an internal surface comprising a stepped portion, such that fluid flow passageway extends in a lateral direction at a point along the pressure relief valve;

wherein the valve walls define a thermal conductive path between an interior of the cryogenic vessel and a surrounding environment;

wherein at least a portion of the thermal conductive path comprises a thermally insulative portion; and

a spool configured to move into an open position when the pressure within the interior of the cryogenic vessel is greater than a threshold pressure, such that the pressure relief valve is open whilst the spool is in the open position;

wherein the thermally insulative portion surrounds the spool;

wherein the spool comprises a substantially cylindrical body and a flange at one end of the spool, wherein the flange extends from the cylindrical body in a lateral direction and has a circumference greater than the rest of the body;

wherein, in the closed position, a face of the flange of the spool perpendicular to the fluid flow passageway presses against the stepped portion of the valve walls.

2 . The pressure relief valve of claim 1 , wherein the thermally insulative portion comprises a non-metallic material.

3 . The pressure relief valve of claim 1 , wherein the thermally insulative portion comprises Polyether ether ketone (PEEK).

4 . The pressure relief valve of claim 1 , wherein the thermally insulative portion comprises a composite material formed of PEEK fibres held together by resin.

5 . The pressure relief valve of claim 1 , wherein the pressure relief valve further comprises:

a filter configured to prevent material from passing through the pressure relief valve from the interior of the cryogenic vessel.

6 . The pressure relief valve of claim 5 , wherein the filter is formed of Inconel.

7 . The pressure relief valve of claim 1 , wherein the spool is formed of Inconel.

8 . The pressure relief valve of claim 1 , wherein the thermally insulative portion extends between mechanical interfaces of the pressure relief valve.

9 . The pressure relief valve of claim 1 , wherein the thermal conductive path is the only path in the pressure relief valve along which heat may travel by conduction between the interior of the cryogenic vessel and the surrounding environment.

10 . A cryogenic vessel comprising:

hydrogen fuel stored in the cryogenic vessel;

a pressure relief valve comprising:

valve walls defining a fluid flow passageway through the pressure relief valve;

wherein the valve walls define a thermal conductive path between an interior of the cryogenic vessel and a surrounding environment;

wherein at least a portion of the thermal conductive path comprises a thermally insulative portion.

11 . The cryogenic vessel of claim 10 , wherein the pressure relief valve further includes:

an internal surface comprising a stepped portion, such that fluid flow passageway extends in a lateral direction at a point along the pressure relief valve; and

a spool configured to move into an open position when the pressure within the interior of the cryogenic vessel is greater than a threshold pressure, such that the pressure relief valve is open whilst the spool is in the open position;

wherein the thermally insulative portion surrounds the spool;

wherein the spool comprises a substantially cylindrical body and a flange at one end of the spool, wherein the flange extends from the cylindrical body in a lateral direction and has a circumference greater than the rest of the body;

wherein, in the closed position, a face of the flange of the spool perpendicular to the fluid flow passageway presses against the stepped portion of the valve walls.

12 . An aircraft comprising:

a cryogenic vessel as recited in claim 11 .

13 . A pipe system comprising:

a pressure relief valve as recited in claim 1 .