Double block and bleed isolation requires two in-line isolation valves and a bleed valve, used to drain or vent trapped fluid between the two closure elements. Double block and bleed valves are ...

However, the upstream seating load is not normally high enough to permit block-and-bleed operation of metal-to-metal seated wedge gate valves. Figure 3-34: Wedge Gate Valve with Plain Hollow Wedge, ...