Centrifugal Pump Research Paper

hat is used to impart energy to a fluid through centrifugal force. Thus, stripped of all refinements, a centrifugal pump has two main parts: (1) a rotating element, including an impeller and a shaft, and (2) a stationary element made up of a casing, casing cover, and bearings. In a centrifugal pump, the liquid is forced by atmospheric or other pressure into a set of rotating vanes. These vanes constitute an impeller that discharges the liquid at its periphery at a higher velocity. This velocity is converted to pressure energy by means of a volute (see Figure 1) or by a set of stationary diffusion vanes (see Figure 2) surrounding the impeller periphery. Pumps with volute casings are generally called volute pumps, while those with diffusion vanes

Other pumps, most often vertical types, are submerged in their suction supply. Vertical-shaft pumps are therefore called either dry-pit or wet-pit types. If the wet-pit pumps are axial-flow, mixed-flow, or vertical-turbine types, the liquid is discharged up through the supporting drop or column pipe to a discharge point above or below the supporting floor. These pumps are consequently designated as aboveground discharge or belowground discharge units.

Figures 3, 4, and 8 show typical constructions of a horizontal double-suction volute pump, the bowl section of a single-stage axial-flow propeller pump, and a vertical dry-pit single-suction volute pump, respectively. The names recommended by the Hydraulic Institute for various pump parts are given in Table 1.

CASINGS AND DIFFUSERS ____________________________________________

The Volute Casing Pump This pump (refer to Figure 1) derives its name from the spiral-shaped casing surrounding the impeller. This casing section collects the liquid discharged by the impeller and converts velocity energy to pressure energy.

A centrifugal pump volute increases in area from its initial point until it encompasses the full 360° around the impeller and then flares out to the final discharge opening.

Instead, the impeller is enclosed in a pipe-like casing. Generally, diffusion vanes are used following the impeller proper, but in certain extremely low-head units these vanes may be omitted.

A diffuser is seldom applied to a single-stage, radial-flow pump, except in special instances where volute passages become so small that machined or precision-cast volute or diffuser-like pieces are utilized for precise flow control. Conventional diffusers are often applied to multistage pump designs in conjunction with guide vanes to direct the flow efficiently from one impeller (stage) to another in a minimum radial and axial space. Diffuser vanes are used as the primary construction method for vertical turbine pumps and singlestage, low-head propeller pumps (see Figure 4).

Radial Thrust In a single-volute pump casing design (see Figure 5), uniform or near uniform pressures act on the impeller when the pump operates at design capacity (which coincides with the best efficiency). At other capacities, the pressures around the impeller are not uniform (see Figure 6) and there is a resultant radial reaction (F). A detailed discussion of the radial thrust and of its magnitude is presented in Subsection 2.3.1. Note