TUTORIAL ON SPECIAL PURPOSE PUMPS-PITOT; PROGRESSING CAVITY; AIR OPERATED DIAPHRAGM; AND HYDRAULICALLY ACTUATED DIAPHRAGM

摘要

There are pumping services characterized by peculiar conditions for which special purpose pumps (quite different from mostly known centrifugal pumps) represent the most effective selection in terms of performance, reliability, maintenance, and cost. The requirements for pumping duties in the industrial processes and civil services can cover a very broad range of conditions in terms of: capacity, head, suction conditions, physical properties of the pumped media, and quality standards for the process products. In most cases, these requirements are mutually conflicting, and so a compromise must be found in order to select the pump type/size that fits the end user needs, both efficiently and economically. In several circumstances, some requirements are critically overriding (special pump services) and consequently dictate the selection of pump types, which operate with pumping principle not quite common or popular (special purpose pumps). The classification of pumps into "common types" and "special purpose" introduced here is mainly in the light of the difficulty of the pumping service, especially as related to performance and/or pumped media. The classification has nothing to do with either the complexity of the pump design (hydraulic and mechanic) or the engineering level of the features incorporated in the pump. On the other hand, the rotordynamic pumps, which include centrifugal-, mixed-, and axial-flow pumps are here considered as "common type" pumps, because they represent the largest fraction of the pump population. Moreover, the rotordynamic pumps, especially centrifugal-flow pumps, are extensively covered in the open literature and so a large amount of technical information is available to the pump designer and end user as well. Sometimes the working physics and construction of the rotordynamic pumps are the best match for difficult pumping services and give the most satisfactory results for the end user.