Abstract: A dispensing system has a gas-powered pump 5 supplied with gas through an inlet 16 from a supply 7 when an actuation valve 11 is operated, the actuation valve also causing the opening of a dispense valve 9 in the outlet 18 of the pump. Gas supplied to the inlet 16 displaces a drive piston 35 against the action of a return spring 41. A rod 31 movable by the drive piston 35 extends into a pumping cylinder 13 where it drives a two-part pumping piston 33 over a substance dispensing stroke. As the substance is being dispensed by the piston 33 a fresh charge of the substance is drawn into the cylinder through a substance inlet 27 connected to a supply 3, which may be a bag-in-box. During the return stroke, lost motion between an inner piston part 43 fixed to the rod 31 and an outer collar-shaped piston part 51 is adjustable by limit switches (109, FIG. 5B) or locking pins (99, FIG. 5A). The actuation valve may be push-button operated (FIGS. 4A and 4B).