Tubular Diaphragm Fire Relief Valve Model 850B-4, FM Approved for sizes 4", 6" & 8", 3-year warranty, Low Head Loss, One spring for all pressure ranges between 30 and 200 PSIG, Cast steel construction, Pressure excursions do not exceed 3% of set pressure, Fusion coated epoxy inside and out, Anti-cavitation design, Nickel aluminum bronze construction option (Alloy C95800), Duplex stainless steel construction option (Alloy 2205), Low maintenance, Simple and reliable operation This valve is a pressure-operated, in-line axial valve. A tube diaphragm actuates the valve, which is comprised of three major components: 1) Tube, 2) Barrier, 3) Body There is only one moving part in the valve: The tube diaphragm. There are no shafts, packing, stem guides or springs. The tube diaphragm is a one piece, homogeneous nitrile rubber part which is extremely durable. The ends of the tube are thick solid rubber, designed to fit between mating flanges. This design eliminates the possibility of cutting the tube diaphragm due to over tightening or piping misalignment during installation. The tube forms a drip tight seal around the barrier when the pressure is equalized between the valve inlet and the control chamber. When pressures removed from the control chamber, the valve is open. The minimum recommended operating pressure is 40 P.S.I. of inlet pressure. STANDARD MATERIALS: Body: Cast steel ASTM A216 WCB, Trim: Bronze ASTM B61, Tube Diaphragm: Nitrile Rubber; Pilot control valve: All parts: 316 SS, O-rings: Nitrile Rubber END DETAILS: Flanged ANSI B16.5, PRESSURE: 250 psig, TEMPERATURE RANGE: 32 to 180 deg F