http://www.highmpavalve.com/ball-valve/trunnion-mounted-ball-valve/low price Trunnion Mounted Ball Valve How Does a Double Block and Bleed Ball Valve Work? Double block and bleed valves are used for isolation in critical applications. They also prevent product contamination and maintain system integrity. DBB valves make it easy to remove machinery for cleaning, repair, and maintenance. Before DBB valves were used, isolating pipelines and machinery was a difficult process. You had to install two individual isolation valves, a spool piece, and a bleed valve to maintain system integrity. The machines were expensive and heavy. There was an increased risk of emission since multiple machines had to be installed. It was also difficult to operate the system since the technician had to check three valves at the same time. API 6D defines a double block and bleed valve as a "single valve with two seating surfaces that, in the closed position, provides a seal against pressure from both ends of the valve with a means of vending/bleeding the cavity between the seating surfaces." There are a couple different styles of double block and bleed valves. One style has two independently seating valves inside, with a bleed or drain valve. This configuration is referred to as a double isolation and bleed (DIB). The DIB valve can isolate either side of the valve (bi-directionally) to vent or bleed the cavity and isolate piping. Which applications require a double bock and bleed valve? Double block and bleed valves are most commonly used in the oil and gas industry, but can also be helpful in many other industries. It's typically used where bleeding the valve cavity is required, where piping needs isolation for maintenance, or for any of these other scenarios: Prevent product contamination Remove equipment from service for cleaning or repair Meter calibration Liquid service near waterways or municipalities Transmission and storage Chemical injection and sampling Isolate instrumentation such as pressure indicators and lever gauges Primary process steam Single Piston Effective (SPE) Design Pd= Medium Pressure Pc= Body Cavity Pressure Ps= Spring Force The medium pressure "Pd" and spring force "Ps" will push the valve seat to the ball and ensure the sealling tightness. When the body cavity pressure increased to a certain value which over than the medium pressure plus spring force, the cavity pressure "Pc" will push the seat apart from the ball, and the cavity pressure release automatically. So this valve seat design can ensure the ball valve both side block and bleed function by medium pressure, as so called Double Block and Bleed (DBB Valves) The pressure test of the DBB valve: The valve is partially opened so that the experimental flow is fully injected into the valve chamber, and then the valve is closed so that the bleeding of the valve body is open and the excess medium is allowed to overflow from the valve chamber test junction. Pressure should be applied simultaneously from both ends of the valve to monitor seat tightness through overflow at the valve chamber test junction. The figure below shows a typical DBB ball valve configuration. When the valve is closed and the valve chamber test port is opened and both ends of the valve are pressurized (or pressurized separately), the valve chamber port detects leakage from each end to the valve chamber. Theoretically, DBB valve can not provide positive double isolation when only one side is under pressure, the valve does not provide positive double isolation when only one side is under pressure. Size Range: 2 to 24" (50 鈥?600mm) Body Materials: ASTM A105, ASTM A350 Gr. LF2, ASTM A182 Gr F316 Temperature Range: -50 to 600掳F (-45 to 315掳C) Stem Materials: ASTM A479 Type 410 17-4PH XM-19 ASTM A182 F316 Pressure Ratings: ASME CL150, 300, 600 Seat Materials: RPTFE, Nylon, Devlon, PEEK, Tek-Fil, TFM Shutoff Rating: Zero Leakage Ball Materials: ASTM A105 w/ENP ASTM A350 Gr. LF2 w/ENP ASTM A182 Gr. F316 ASTM A182 Gr. F316 w/ENP Body Style: Two Piece, Three Piece Design Standard: API 6D, ASME B16.34low price Trunnion Mounted Ball Valve website:http://www.highmpavalve.com/ball-valve/trunnion-mounted-ball-valve/