A pump apparatus for pumping undergound fluids from a well. The pump includes inner and outer chambers, and a float slidable within the outer chamber. A source of compressed air is directed to a valve on the pump. The valve controls the flow of the compressed air into the outer chamber during the pumping cycle, and also controls the opening of a vent during the intake cycle. The float, while sliding up and down within the outer chamber in response to the fluid level within the chamber, activates the valve to begin the pumping of fluid when the chamber is full. When the chamber is empty, the float activates the valve is turn off the compressed air.