<b>Flow Pumps</b>
The best known representative of the flow pumps and often found on board ships is the centrifugal pump.
It uses centrifugal force to move the fluid. For this reason they are also called centrifugal pumps. The medium to be conveyed enters the centrifugal pump (spiral housing) via the suction pipe, is picked up by the rotating pump wheel and carried outwards on a spiral path. The outwardly decreasing radial velocity of the liquid, which is imposed as a result, leads to an outwardly increasing pressure inside the pump, which conveys the liquid into the pressure pipe arranged tangentially on the spiral housing. If the impeller and housing are designed accordingly, liquids mixed with solids (e.g. waste water) can also be pumped. A measure of the permissible solid size is the so-called ball passage, specified as the maximum diameter of the ball that the pump could pass.
Unlike positive displacement pumps, standard centrifugal pumps are not self-priming. They must therefore be filled with the fluid from the start-up. To do this, they are installed in the inflow of the medium to be conveyed. If this is not possible, the pump and the suction line must be filled, e.g. using a piston pump, before starting. A special design of the centrifugal pump, the side channel pump, is however self-priming; filling before starting is not necessary.
However, centrifugal pumps have the advantage over piston pumps that they deliver continuously and the delivery rate can be regulated continuously at a constant drive speed (by throttling) or by changing the speed.
Despite different designs of the pump housing, arrangement of suction and discharge nozzles, number and shape of the impellers and guide devices in the pump, they all follow a basic design principle. It generally comprises two vane systems, one of which is connected to the housing (guide device) and rests, while the other is connected to the drive shaft and rotates (impeller).
With a single-stage pump, delivery heights of around 150 m WS can be achieved on average, which corresponds to a pressure of around 15 bar.
According to the attainability of the maximum pressure one also speaks of:
Low pressure pumps: up to about 1 bar
Medium pressure pumps: up to about 6 bar
High pressure pumps:> 6 bar
Flow Pumps
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