A fluid system for example for steam raising comprising a flow control device (20), means (28) to supply a head of fluid to the flow control device (20), and at least one fluid using means such as a flash boiler (12-14), the flow control device (20) comprising a chamber (48), an inlet (49) to the chamber from the fluid supply means (28), and an outlet (21-23) from the chamber (48), a valve means (40) associated with the outlet (21-23) operable to direct fluid from the outlet (21-23) either to the fluid using means (12-14) or to a relief means (43-45).