Importance

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Abstract

An improved method for precision control of a wide variety of work material liquids and an improved pinch valve incorporating that method is disclosed. The method involves constricting a discrete site on a resilient tube having liquids flowing therethrough to pinch off flow, then moving the constriction upstream to maintain flow stoppage and create a partial vacuum to cause positive suck back, the distance the constriction is moved being selectively determinable to selectively adjust suck back. An apparatus for practicing the method comprises an external roller shutoff member which is movable in a direction to intersect with and then move counter to work material flow within a resilient tube to compress the tube against a ramp and gives positive repeatable shutoff of the flow. The further upstream movement of the roller shutoff member after reaching the shutoff position allows the natural resilience of the tube to return from its compressed to its natural uncompressed position and thereby create a partial internal vacuum which in turn creates a positive suck back of work material at the outlet to provide dripless precise shutoff. The flow through the tube is unobstructed when the valve is in open position. The valve is biased closed and is selectively actuable against the bias to open position. The amount of travel of the roller shutoff member after shutoff is adjustable to adjust suck back for different conditions and different work materials. The movement of the shutoff member is uncomplicatingly linear for easy selective actuation. The rolling cooperative action of parts during shutoff and suck back permits control of flow of work liquids with particulates therewithin without destruction of the parts from the particulates to provide long life with repeated cycling.

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First Claim