A lift pump is actually an airlift pump which uses compressed air to lift water from underground.Air from the compressor is blown at the lower end of the pipe that transports the water.The air bubbles rise quickly above the water due to buoyancy.Due to fluid pressure the water also moves along with the air bubbles and thus reaches the upper end of the transport pipe.
An Airlift pump is a pump that has low suction and moderate discharge of liquid and entrained solids. The pump injects compressed air at the bottom of the discharge pipe which is immersed in the liquid. The compressed air mixes with the liquid causing the air-water mixture to be less dense than the rest of the liquid around it and therefore is displaced upwards through the discharge pipe by the surrounding liquid of higher density. Solids may be entrained in the flow and if small enough to fit through the pipe, will be discharged with the rest of the flow at a shallower depth or above the surface. Airlift pumps are widely used in Aquaculture to pump, circulate and aerate water in closed,recirculating systems and ponds.