Fluid system

A fluid system configured to control delivery of gas turbine engine bypass duct cooling air in a gas turbine engine, the fluid system comprising:

• a bifurcation fairing located in a bypass duct of the gas turbine engine, the bifurcation fairing having including:
• a nose portion that blends into one of a plurality of upstream outlet guide vanes of the gas turbine engine;
• a delivery conduit inlet proximate to the nose portion, the delivery conduit leading to a pre-cooler arranged to cool air for use in environmental control;
• a delivery conduit connected to the delivery conduit inlet, the delivery conduit being configured to deliver bypass duct cooling air to the pre-cooler;
• a diverter conduit having a diverter conduit inlet disposed upstream of the pre-cooler and extending to an outlet disposed in a location other than the pre-cooler;
• a valve configured to selectively partially close the delivery conduit and selectively partially close the diverter conduit, the valve being configured such that opening of the diverter conduit by the valve closes the delivery conduit by the valve and vice versa;
• and
• one or more transit channels through which in use the air supplied by the delivery conduit passes and is exhausted to an exhaust conduit having an outlet from which the air is vented, wherein
• the delivery conduit, the one or more transit channels, the exhaust conduit and the diverter conduit are sized such that actuation of the valve throughout a range of operation of the valve causes substantially no variation in pressure at the delivery conduit inlet.