A gas pressure driven fluid pump comprising a pump tank having a liquid inlet and a liquid outlet. A float, carried within the interior of the pump tank, is operable to move between a low level position and a high level position. A snap-acting valve control mechanism uses magnetic interaction to switch between exhaust porting and motive porting. Fluid exiting the pump tank causes the float to fall from the high level position to the low level position due to introduction of motive gas during motive porting. Exhaust porting begins when the float falls to the low level position.