Pumps for liquids have been around for a long time, as water-wheels for 3000 years and as worm-screws, not quite that long. One distinguishes between displacement- and flow-distribution pumps. Displacement pumps move liquids by changing the volume and the respective controlled opening and closing of of inlets and outputs. The volume can be changed either by reciprocal or the rotating displacement pump.
Flow-distribution pumps, as opposed to displacement pumps, are more sensitive to substances containing gaseous inclusions. Basically, they are also not self-priming, unless they are fed. They also cannot, however briefly, transport gases. Therefore, they mostly provide a more even delivery-flow. Indeed, the displacement pumps are responsible when higher pressures occur, very high pressures are possibly better handled by the reciprocal displacement pump. 04/12
Pumps