Abstract: Molten metal is pumped from a furnace to a place where it is utilized using a gas-plunger pump having a container holding the chamber with an inlet for drawing metal from the furnace to the chamber, and with an outlet for forcing metal out of the chamber to the place of use. The inlet and outlet are disposed at the bottom of the chamber. A suction and pressure system includes a closed circuit containing a vacuum tank, a pressure tank, a vacuum pump/compressor unit connected between them, and a first valve. The closed circuit is connected to the chamber via a conduit. A control system alternately connects and disconnects the vacuum tank and pressure tank and substantially synchronously alternately opens and closes the inlet and outlet by actuation of valves associated with the inlet and outlet.