(57) A fluid control valve comprising means defining a flow path for fluid (16), a variable
flow restrictor in said flow path comprising a wall member (5) bounding a portion
of said flowpath, and having flow passages (19) therethrough, means (20) for at least
substantially closing a portion of said wall member against fluid flow therethrough,
means (6) for producing relative movement between said wall member and said closure
means to vary the area of said wall member exposed for fluid flow therethrough, the
size of the flow passages through said wall member being such that there is at least
one inlet pressure at which the valve with at least a substantial portion of the wall
member exposed for fluid flow will produce a pressure drop substantially equivalent
to the inlet pressure.
Preferably, said valve will produce said pressure drop at inlet pressures above 498
Pa (2 inches water gauge).
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