Abstract: Pinch valves having a flexible, constrictable sleeve are used to control a dilution headbox for a paper making machine. A variety of pinch valves may be used in the present invention with the pinch valves being actuated by pneumatic or hydraulic pressure or by mechanically pinching the valves' sleeves by means of rams driven by stepper or linear drive motors. For pneumatic control, dynamic differential pressure drops are measured across the valves to determine flow rate through the valves. A pinch valve, referred to herein as a torsional pinch valve, is disclosed for dilution headbox control. In one form, a first end of a sleeve is fixedly mounted in a support frame and the second end of the sleeve is mounted for rotation in the frame. A driver rotates the second end of the sleeve such that a flow path through the sleeve is controlled. The flow path is a maximum when no torsion is placed on the sleeve and is reduced to substantially zero by sufficient rotation.