Temperature-responsive valve apparatus

A fusible cap 50 for a valve body, possibly a gate valve, comprises assembly shell 52 which is secured to valve bonnet 20, close to valve closure stem 32, 34, and a fusible component 54, perhaps eutectic, that allows the operative displacement of stem 32, 34 when a predetermined temperature has been reached, possibly 120 degrees Celsius. Shell 52 may be a cylindrical ring and threaded to bonnet 20. Component 54 may be a disc secured to shell 52 and may abut with stem 32, 34. The driving mechanism to move stem 32, 34 in one direction may be the flow fluid pressure, while the force to move stem 32, 34 in the other direction may be given by a different fluid pressure applied to piston 26 or diaphragm (39, Fig 5) in bore 28. The different fluid pressure may be provided by a fluid motor, perhaps a hand pump. The valve apparatus is intended for use in remote locations for fire extinguishing around hydrocarbon wellheads. Also provided is a fire control system featuring valves controlled by fusible stem blocks to release fire control fluid and a hydrocarbon producing wellhead with a valve that can be opened when a fusible element is removed, but is biassed closed by the pressure of the fire control fluid.