Valve with truncated aperture providing enhanced rangeability and logarithmic flow characteristic

A control valve comprising:

• a valve body having therein a slide chamber and an inlet passage and an outlet passage at respective opposite sides of the chamber, the inlet passage having a cross-sectional flow area defined by a peripheral shape comprising a substantially straight leading edge disposed substantially perpendicular to the direction of travel of the plug member defined below and a closure periphery, the inlet and outlet passages cooperating to partially define a flow passageway intersecting the slide chamber;
• a plug member mounted for movement within the slide chamber and having a flow orifice extending transversely therethrough, the plug member and its flow orifice being each dimensioned and configured to seal the flow passageway when the flow orifice is out of registration with the flow passageway and to complete the flow passageway by connecting the inlet and outlet passages in flow communication when the flow orifice is registered therewith, at least a segment of the flow orifice being dimensioned and configured to comprise a tapered slot portion with a cross-sectional flow area less than that of the flow passageway, the tapered slot portion (a) having in flow cross section the shape of an isosceles triangle, the legs of which subtend at their apex ends an angle of from about 45 to 90 degrees, and (b) being narrower than the width of the flow passageway over at least a majority of its length and defining a triangular cross-sectional area smaller that that of the inlet passage;
• the tapered slot portion of the flow orifice and the inlet passage being dimensioned and configured so that as the plug member moves from a fully closed position to an intermediate throttling position, the legs of the isosceles triangle first transect the inlet passage at the leading edge thereof whereby to define, for a portion of the travel of the plug member, a flow passageway having a triangular cross-sectional flow area, the flow orifice further having an associated base portion with a cross-sectional flow area at least as wide as the cross-sectional flow area of the flow passageway, and being dimensioned and configured so that when the base portion is fully registered with the flow passageway, the valve is fully open to flow therethrough and when the tapered slot portion or part thereof is registered with the flow passageway, the valve is partially open for flow therethrough;
• and
• positioning means operatively connected to the plug member to position the plug member at selected incremental locations within the slide chamber to selectively adjust registration of the flow orifice with the inlet and outlet passages at fully open, fully closed and a plurality of intermediate throttling positions.