MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

Chapter 3PositiveDisplacement Methods3.1 IntroductionAs can be seen from Table 2.2, the positive displacement class ofwater lifters comprises a wide variety of methods within the two majorsubclasses, reciprocating and rotary, and additionally, several otherdevices which do not truly fit into either of these subclasses. Unlikethe kinetic class, which due to its relatively recent development (see1.2) is comprised primarily of modern, commercially manufactured pumps,positive displacement devices range from the early bucket and rope to thewaterwheel, to the modern direct-acting piston and peristaltic pumps.However, all these water lifters have one thing in common which is thebasis for theirclassification.3.2 Reciprocating MethodsEach of these methods provides displacement of water from one head(elevation and/or pressure) to another by a reciprocating motion betweenthe two heads. It is appropriate that this subclass is the first to bereviewed since it comprises the first devices man developed when he wantedto liftmore water than he could hold in his two cupped hands.3.2.1 BailingAll the methods in this category are simply based on allowing waterto fill a container and raising that container to a desired height. Themeans by which this lifting is accomplished is the criteria for furtherclassificationand discussion.28