Abstract: A fluid injector particularly for injecting fluid into a furnace comprises a housing structure having inlet and outlet ports; a pair of fluid connections and means defining passageways for fluid between the ports and respective ones of the fluid connections; and valve means for controlling the flow of fluid along said passageways; a body assembly including an elongate tubular portion having provision for receiving a nozzle at its outer end; a pair of fluid connections and means defining passageways for fluid between each of the fluid connections and said outer end of the tubular portion; said housing structure providing a support for the body assembly and including fluid pressure means for displacing the assembly relative to the housing between a first position, in which the fluid connections on the body assembly are coupled to respective fluid connections on the housing structure, and a second position, in which the fluid connections on the body assembly are disconnected from the fluid connections on the hou