In this standard, OSHA provides a couple of relevant definitions: "Isolation means" the process by which aBall Valves permit space is removed from service and completely protected against the release of energy and material into the space by Resilient Seated Gate Valvessuch means as: blanking or blinding; misaligning or removing sections of lines, pipes, or ducts; a double block and bleed system; lockout or tagout of all sources of energy; or blocking or disconnecting all mechanical linkages. "Double block and bleed" Automatic Control Valvesmeans the closure of a line, duct, or pipe by closing and locking or tagging two in-line valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves. The simplest form of Butterfly Valvesa double block and bleed setup is two gate valves with a short pipe between them with a small, typically 3/4" "bleeder" gate valve in between them. The two primary gate valves can be closed and the bleeder opened to bleed off any fluid which is trapped Bellows Seal Valvesor is entering through a leaking upstream valve. The likelyhood of the fluid continuing through the downstream valve with no pressure to drive it is minimal, thus protecting the downstream piping (or equipment) from the fluid.

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