Abstract: A wire helix having adjacent turns normally spaced so that the wall of a flexible tubing will be pinched closed when placed between them has at least one pair of turns spaced far enough apart to allow the tubing to pass between them without being pinched; valving action takes place when the tubing is twisted around the helix to move it between the unobstructed position to the pinched position. In a modified form, there are two locations in the helix where the tubing may pass outwardly and then reenter the helix without being obstructed; in this form, the looped portion of the tubing lying outside the helix may be rotated about the helix in either direction to pinch it closed.