There is disclosed a pressure responsive valve 352 for controlling a cooling flow through an orifice 320 in a gas turbine assembly 300. The valve 352 comprises an attachment point 360, a valve element 358, and a compressible valve body 354 defining a chamber 355 for sealing a volume of compressible gas. The valve body 354 is configured to act between the attachment point 360 and the valve element 358 so that in use expansion or contraction of the valve body 354 in response to external pressure causes the valve element 358 to move relative the orifice 320. A corresponding kit, method of installation and gas turbine assembly are disclosed.