Importance

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Abstract

A hand pump having a cylinder and piston in which the piston head is formed with an annular channel having an opening in the base of the annular channel in free communication with the interior of a hollow piston rod. A pair of radially-projecting stops extend outwardly from the base of the channel adjacent the opening. A pair of O-rings are positioned within the channel with one on either side of the stops with the O-rings having an inner diameter closely fitting the surface of the base and an outer diameter when in an unstressed position engage in a sliding relation the inner surface of the cylinder. Chambers are formed on either end of the piston head and are provided with valve inlets. In operation the O-rings are alternately flexed about the stops to create an air passage between the flexed O-ring and the inner surface of the cylinder depending upon the relative direction of movement of the head to the inner surface of the cylinder wall, whereby air may be forced from one or the other chambers through the hole and into the hollow piston rod.

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First Claim