The FCV electropneumatic proportional-flow valve from Proportion-Air Inc., McCordsville, Ind. (proportionair.com), lets operators adjust its valve opening (Cv) linearly from 0 to 19 using electronic controls. It also uses a parabolic valve plug designed so that the area of the valve opening is proportional to valve position. So a valve at 50% of its stroke is also at 50% of its maximum flow rating. An LVDT provides continuous feedback on valve position. Resolution is 0.3% and linearity is ±5%. LEDs indicate power and TTL. The valve, which can be normally open or closed, accepts 1 to 10-V or 4 to 20-mA command signals and is powered by 15 to 24 V at 250 mAdc. Maximum working pressure is 250 psig, and loading pressure ranges from 80 to 120 psig. End connectors use 1-in. NPT threads.