Volumetric pump with replaceable reservoir assembly

Claim 1

A volumetric pump, comprising: reservoir means for providing a reservoir of variable volume, including a piston located within the reservoir means which when axially displaced causes a change in reservoir volume; drive means in mechanical connection with the piston, for displacing the piston when such means is engaged against a rotating member having a component of angular velocity in the direction of piston displacement, such drive means having an interior drive surface that is substantially a longitudinal section of a surface of revolution about a first axis substantially parallel to the direction of piston displacement, such interior drive surface being threaded for a length at least as great as the desired total piston displacement; a rotating, axially non-displaceable drive screw which is short in comparison to the displacement of the piston and has an axis or rotation approximately coincident with the first axis, in engagement with the interior drive surface, for displacing the piston; wherein the reservoir means and drive means form an assembly that is removably engageable against the drive screw; and sever-connection means, for temporarily connecting the piston to the drive means, for movement of the drive means when so connected to the piston both to increase and to decrease the volume of the reservoir means, in such a way that the sever-connection means must be severed to permit placing of the drive means in engagement with the drive screw, and so that following such severence the piston is no longer connected to the drive means and can then be moved only to decrease the volume of the reservoir means.