Series BFF Flanged Externally Controlled Pilot Float Valve flange sizes DN50 to DN350 with special sizes to DN1400. Body material Bronze, Ductile Iron Epoxy Coated, 304 or 316 stainless steel. The BFF pilot float valve uses a pilot sub valve (not supplied) to control the main BFF valve. When the water level elevates to the full water level set by the sub valve (floating ball switch), the sub valve (floating ball switch) closes and the back pressure chamber inside the main BFF valve rapidly accumulates pressure that in turn pushes the main BFF float valve piston into the closed position, thus stopping the water tank refill. By this system the float valve mechanically controls the tank water level. In order to save space inside the tank and for easy maintenance and inspection it is recommended to install the BFF float valve outside of the tank. The BFF pilot float valve is an ideal solution for maintaining water tank levels and does not require any electricity or electrical systems and only requires the pilot float ball and a small amount of external pipework (not supplied).