There are a number of different types of water pumps that operate according to different principles. For lots of information, including pictures and diagrams, do an internet search on water pump.
Water pumps are available in different types. 1. Centrifugal type: Operate by increasing the velocity of water which, when the velocity is decreased by the Volute casing, the pressure increases. 2. Rotary Gear type.: Operate by Displacement of the water by rotating, gears that trap water between the teeth of 2 rotors of inter-meshing gears that release the water at a higher pressure on the opposite side of the pump to the intake. 3. Piston (reciprocating type: Also a displacement operation by a piston moving backwards and forwards within a cylinder (like a hypodermic syringe in operation). Back stroke takes water into the cylinder and forward stroke discharges it at a higher pressure. (Double acting types are also used that take in and discharge alternately from both ends).
