Depressurisation valve

A depressurization valve for a cooling circuit comprising:

• a main chamber having a main valve, the main valve being located to seal a path of the cooling circuit, and
• a pilot line having a secondary valve and a blowdown line, the main chamber being connected to the cooling circuit via the pilot line, the pilot line allowing coolant to enter the main chamber, the blowdown line allowing coolant to escape from the main chamber, and the pilot line having a lower fluid resistance than the blowdown line, wherein:
• in normal operating conditions, the main valve is configured to be maintained in a closed position by a pressure of the coolant, and under elevated temperature or pressure conditions, with respect to the normal operating conditions, the main valve is configured such that when fluid is prevented from entering the main chamber via closure of the secondary valve on the pilot line, pressure on the main valve is reduced and the main valve moves to an open position, and
• the secondary valve is a high pressure latching isolation valve.