A flow control valve has a stationary member provided with an orifice plate together with a ported cup which slides within the opening in the orifice plate against the action of a spring, to provide substantially constant rate of flow under varying differential pressures across the cup. The ported cup has a generally cylindrical side wall and an end wall, the side wall having an outer surface comprising a first cylindrical surface near the end wall and a concentric second cylindrical surface axially spaced therefrom of smaller diameter, and a tapered surface joining the first and second cylindrical surfaces. Ports in the side wall extend through at least one of said cylindrical surfaces. This construction provides a minimum port area change which is lower than the range which can be obtained with the minimum width of a single port segment.
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