Although most single-stage pumps have volute casings, both volute and diffuser casings are used in multistage pumps. Advantages of the volute casing are described in Chapter 2. However, the diffuser casing or collector is a very strong competitor of the volute design in high-pressure applications. The principal reason for this is that for the same pump capacity, a diffuser design is smaller (occupies less volume) than a volute, thus making a diffuser pump less expensive to manufacture. When compared to integrally cast volutes, the volume advantage of a diffuser design is compounded by symmetry, an absence of complicated castings, suitability for radially split construction, and more uniform expansion in high-temperature service. Arranging twin volutes in the same manner as diffusers (Fig. 2.10) overcomes all the advantages except that of lower volume for the same capacity. At that point, the choice between twin volutes and diffusers must be made based on pump cost versus operating cost, the broader efficiency characteristic of the volute being an advantage when the pump has to run over a wide flow range. There is evidence, too, that at conditions far from BEP, twin volutes produce lower rotor forces than diffusers.
KeywordsOuter Casing Volute Casing Split Casing Axial Split Flange Joint
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- [3.1]API-610, 8th Edition, Centrifugal Pumps for Heavy-Duty Chemical, Gas Processing, and Refinery Service 1995, American Petroleum Institute, Washington, D.C.Google Scholar