Pump

Claim 2

A metering piston pump including a vertical cylinder having a smaller diameter bore portion and a greater diameter bore portion at the lower end of said smaller diameter bore portion, a piston rod extending coaxially through the cylinder, a piston disposed at the upper end of said piston rod and dimensioned to conform closely with said smaller diameter portion of the bore for sealing-tight pumping operation therewithin, means for driving said piston upwardly and downwardly along said narrow diameter bore portion, means for optionally withdrawing the piston down into said larger diameter bore portion and for guiding the piston coaxially of the larger diameter bore portion, drain means communicating with the bottom of said wider diameter bore portion, and seal means in the lower end of said cylinder and surrounding said piston rod for guiding liquid draining into said larger diameter bore portion from the piston and the smaller diameter bore portion to drain away through said drain means when the piston is withdrawn entirely into the larger diameter bore portion.

Claim 3

A pump as set forth in claim 1, and further including second means normally preventing withdrawal of the piston from said smaller diameter bore portion into said larger diameter bore portion, and override control means for operating said second means to allow withdrawal of the piston into tHe larger diameter bore portion.

Claim 4

A pump as set forth in claim 2, wherein said second means comprise limit switch means actuable to prevent further movement of the piston in a withdrawal direction once the piston arrives at one end of the smaller diameter bore portion.

Claim 5

A pump as set forth in claim 3, and including further limit switch means effective to stop movement of the piston once the first mentioned limit switch means have been overriden by said override control means to allow the piston to be withdrawn into the larger diameter bore portion.

Claim 6

A pump as set forth in claim 1, wherein said piston has a piston head of conical configuration; and the cylinder has an upper end also of conical configuration said conical piston head and cylinder end being shaped to conform closely to one another to define, in the uppermost position of the piston, a small working space between the conical piston head and the conical end wall of the cylinder.

Claim 7

A pump as set forth in claim 1, wherein said piston has a first predetermined position in said larger diameter bore portion fully withdrawn from said smaller diameter bore portion, a second predetermined position within that end of said smaller diameter bore portion adjacent the larger diameter bore portion, and a third predetermined position at the other end of the smaller diameter bore portion, and further including first electric motor means for driving said piston in a continuous stroke along the cylinder between said second and third predetermined positions, further electric motor means operable at a higher speed range than the first electric motor means for driving said piston between said first and third positions, means for interrupting driving engagement of said first electric motor means and said piston when said further electric motor means is electrically energized, and means responsive to arrival of said piston at said second predetermined position when being driven by said further electric motor means towards said first predetermined position for electrically de-energizing said further electric motor means and for simultaneously effecting driving engagement between said first and second electric motor means.