In the closed
position, high pressure air or other gas enters the space between the back of the seal
face and the insert ring to cause the seal face to expand onto and around the periphery
of the dome component. Material particles are entrapped by the seal against the dome
surface, irrespective of particle size or shape. Before opening the valve, the seat is
relaxed, and the controlled gap is reestablished before the dome component moves to its
open position. The seal is a
loose component clamped into place by a spigot piece and external fasteners holding the
top plate assembly to the body. The seal is easily removed for inspection.
U.S. Patent No. 4,137,935
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