ValvesDOE-HDBK-1018/2-93TYPES OF VALVESSome parallel disk gate valves used in high pressure systems are made with an integralFigure 8 Parallel Disk Gate Valvebonnet vent and bypass line. A three-way valve is used to position the line to bypass inorder to equalize pressure across the disks prior to opening. When the gate valve isclosed, the three-way valve is positioned to vent the bonnet to one side or the other. This prevents moisture from accumulating in the bonnet. The three-way valve ispositioned to the high pressure side of the gate valve when closed to ensure that flowdoes not bypass the isolation valve. The high pressure acts against spring compressionand forces one gate off of its seat. The three-way valve vents this flow back to thepressure source.Rev. 0ME-04Page 13
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