Metering dispenser having suck-back through nozzle

Claim 1

A metering dispenser for supplying a metered quantity of liquid comprising: a housing having an inlet, an outlet and a cavity interposed said inlet and outlet; a piston having a transfer chamber therein, said piston mounted in said cavity and cooperating with the cavity to define a metering chamber; siad metering chamber communicating with said inlet and outlet; first means for sealing said metering chamber, said sealing means mounted to said piston, said first sealing means being operable to terminate communication between said inlet, and outlet with said metering chamber; a passage within said piston, said passage having one end communicating with said metering chamber and an opposite end terminating in said transfer chamber of the piston, said transfer chamber communicating with said outlet when said piston is in a first predetermined position; means for terminating communication between said transfer chamber of the piston and said outlet; second means for sealing mounted to said piston adjacent said transfer chamber, said transfer chamber interposed said first and second sealing means; a reservoir complementary with said housing, said reservoir communicating with said inlet of said housing; and means for actuating said piston, said actuating means pivotally attached to said housing and said piston for moving said piston from a fully extended position to a fully retracted position, wherein, when said piston is in a fully extended position and a liquid fills said metering chamber by way of said inlet while said first sealing means seals said outlet and said piston is moved from said fully extended position to said fully retracted position, said first sealing means seals said inlet so that, said piston moves said liquid from said metering chamber through said passage and into said transfer chamber of the piston, said means for terminating communication between said transfer chamber and said outlet preventing said liquid from escaping through said outlet until said piston moves to said first predetermined position towards said fully retracted position, said transfer chamber communicating with said outlet to expel said liquid from said dispenser after said piston moves to said first predetermined position towards said fully retracted position, said transfer chamber expelling said liquid from said metering chamber, passage and transfer chamber, while said piston is moving to said fully retracted position, said transfer chamber further communicating with said outlet to draw in ambient air to expunge said outlet, passage and transfer chamber of any liquid remaining therein while said piston moves from a fully retracted position to said first predetermined position, said metering chamber developing a vacuum when said piston moves toward said fully retracted position past said first predetermined position, said vacuum aiding the filling of said metering chamber with liquid from the reservoir through said inlet after said first sealing means moves to unseal said inlet.