Flowserve 1878 Double-Disc Gate Valve - Manual (Page 3)

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1.0 PHYSICAL DESCRIPTION AND OPERATION OF EQUIPMENT
1.1
Double Disc Gate Valves
The Flowserve Corporation double disc design is unique in that there are two
independent discs. During each closing stroke, immediately prior to the disc
seating, each disc rotates a few degrees in the plane of the seats. This rotating
feature allows the disc to seat in a different position on each closing stroke,
providing for equal wear and preventing small imperfections from being agitated into
major leakage problems.
The wedge assembly is designed to impart sufficient thrust to each disc to maintain
acceptable low pressure seat leakage. As the differential pressure across the disc
increases, the seating load also increases, thus maintaining acceptable leakage
through the entire range of operating differential pressures. Since the discs are
completely independent of each other and the design is essentially symmetrical,
zero leakage can be maintained in either direction depending only on the direction of
flow. This feature eliminates the necessity of installing a check valve to stop reverse
flow.
To operate these manual valves, turn the handwheel in a clockwise direction for
closure and counterclockwise for opening.