Finger valve series VHK has a large effective area of 2.0 to 17.5mm. This series begins with a minimum tube O.D of 4. The valve direction clearly indicates whether the valve is open or closed (shut to open is counter- clockwise). Classification of knob by color difference facilitates distinction between 2 port valves (gray) and 3 port valves (blue). The optional flame resistant model s knob, whether using the 2 or 3 port valve, is red.