Patent ID: 8235252

Claim:
An apparatus for controlling the flow of material in a material handling apparatus comprised of a material container having a discharge opening, said apparatus comprising: a) discharge conduit extending from the discharge opening; b) a valve having a fully open position and a fully closed position controlling the flow of material from said container through said discharge conduit, said valve including a valve stopper and a valve seat; c) a non-magnetic rod carrying first and second axially spaced solenoid armatures, said rod having a connector end connected to said valve stopper and extending from said stopper within said discharge conduit, said rod and said armatures having cross-sectional areas less than the cross-sectional area of said conduit, said rod and first and second armatures each having cross-sectional areas that are in the range 10% to 50% of the cross-sectional area of said discharge conduit, whereby material can flow between said conduit and said armatures; d) a first solenoid coil surrounding said conduit to bias said first solenoid armature toward said valve's open position; e) a second solenoid axially spaced from said first solenoid, said second solenoid coil surrounding said conduit to bias said first armature toward said valve's closed position; f) a linear variable differential transformer (LVDT) responsive to the position of said second solenoid armature to provide an instantaneous valve position signal; and g) a valve position control means adapted to receive a valve position feedback signal from the LVDT and a desired valve position set point signal, said means urging said valve stopper to the desired valve position set point.