Device to lift, transfer, or increase the Pressure of a fluid (liquid or Gas - see States Of Matter) or to create a Vacuum. In a simple reciprocating pump used to lift Water, a piston moves back and forth in a cylinder equipped with intake and outflow
valves. On the piston's upstroke, atmospheric pressure Forces water into the empty space beneath the piston. On the downstroke, the water
in the cylinder is forced to flow above the piston. Reversing direction, the
piston moves up, allowing more water to come up under it into the cylinder and
lifting the water held above it to an outlet pipe. The rotary pump is like the
reciprocating pump in that it allows a fluid to fill a space that then decreases
in volume. The rotary pump, however, has no valves and uses rotating components
in place of a piston. A jet pump (e.g., a perfume atomizer) uses a fast-moving
stream of liquid or Air as the moving force. Compressors are used to force air or other gases into a closed container.