Lance pump having vertically mounted stepper motor

A pump includes a pump body and an elongate tube. The pump includes an elongate core slidably received in the tube, a stepper motor having a selectively rotatable output shaft extending vertically and a transmission for effecting relative reciprocating motion between the core and the tube. The pump includes an inlet check valve mounted inside the core defining with the core an expansible and contractible lower pump chamber. The inlet check valve is oriented to open during each upward pumping stroke. The pump includes an annular upper chamber above the lower pump chamber and a lateral passage connecting the lower pump chamber to the annular upper chamber. The lateral passage has a check valve oriented to open during each downward pumping stroke. The pump includes an outlet passage connected to the annular upper chamber permitting viscous liquid to flow to the outlet passage on each upward and downward pumping stroke.