Flexible Vane Pumps
Here a flexible toothed rotor is used, generally made of rubber,picture 1. This is very simple in concept, being like a revolving door, but it can involve both considerable friction and significant back leakage. It cannot therefore be considered as an efficient type of pump. On the positive side, it will readily self-prime and can achieve a high head at low rotational speeds. Much will depend on the quality of the rotor material and the type of internal surface of the casing so far as both friction and durability are concerned.
picture 1
Another similar type, developed recently by Permaprop Pumpen in Germany, has an endless rubber toothed belt which is driven around two pulleys; (see picture 2). As it curves around a pulley, the teeth on the belt spread apart and increase the volume between them, thereby drawing in water. The diagram shows how both sides of the chamber simultaneously pump in opposite” directions, and suitable channels in the casing direct the water. The advantages claimed by the manufacturers are, inter alia, that it can run on “snore” indefinitely - (i.e. pumping a mixture of air and water), it will readily self-prime and suck water up to 8m and lift it a further 45m under the power of a small portable single cylinder engine. It is therefore a much more versatile pump than the equivalent centrifugal pump, but it is more complicated and expensive.
picture 2
