In an axial flow pump, the impeller pushes the liquid in a direction parallel to the pump shaft. The impeller of a typical radial flow pump and the flow through a radial flow pump are shown in Figure 6.įigure 6: Radial Flow Centrifugal Pump Axial Flow Pumps In a radial flow pump, the liquid enters at the center of the impeller and is directed out along the impeller blades in a direction at right angles to the pump shaft. The three types of flow through a centrifugal pump are radial flow, axial flow, and mixed flow. The manner in which fluid flows through the pump is determined by the design of the pump casing and the impeller. The result is suction pressure on both sides of the impeller hub, which maintains a hydraulic balance of axial thrust.Ĭentrifugal pumps can be classified based on the manner in which fluid flows through the pump. The balancing holes have a total cross-sectional area that is considerably greater than the cross-sectional area of the annular space between the wearing ring and the hub. The impeller sometimes contains balancing holes that connect the space around the hub to the suction side of the impeller. Figure 5 illustrates examples of open, semi-open, and enclosed impellers.įigure 5: Open, Semi-Open, and Enclosed Impellers Enclosed impellers are also referred to as shrouded impellers. The enclosed impeller has circular plates attached to both sides of the blades. The semi-open impeller is constructed with a circular plate (the web) attached to one side of the blades. The open impeller consists only of blades attached to a hub. Impellers can be open, semi-open, or enclosed. A comparison of single and double volute centrifugal pumps is shown on Figure 2.įigure 2: Single and Double Volutes Diffuserįigure 4: Single-Suction and Double-Suction Impellers In some applications the double volute minimizes radial forces imparted to the shaft and bearings due to imbalances in the pressure around the impeller. Pumps of this type are called double volute pumps (they may also be referred to a split volute pumps). The fluid is then discharged from the pump through the discharge connection.Ĭentrifugal pumps can also be constructed in a manner that results in two distinct volutes, each receiving the liquid that is discharged from a 180° region of the impeller at any given time. This converts the velocity head to static pressure. The purpose of the volute is to collect the liquid discharged from the periphery of the impeller at high velocity and gradually cause a reduction in fluid velocity by increasing the flow area. The volute is a region that expands in cross-sectional area as it wraps around the pump casing. The vanes of the rotating impeller impart a radial and rotary motion to the liquid, forcing it to the outer periphery of the pump casing where it is collected in the outer part of the pump casing called the volute. The pump casing guides the liquid from the suction connection to the center, or eye, of the impeller. The pump casing has suction and discharge penetrations for the main flow path of the pump and normally has small drain and vent fittings to remove gases trapped in the pump casing or to drain the pump casing for maintenance.įigure 1 is a simplified diagram of a typical centrifugal pump that shows the relative locations of the pump suction, impeller, volute, and discharge. The pump casing provides a pressure boundary for the pump and contains channels to properly direct the suction and discharge flow. Centrifugal pumps enjoy widespread application partly due to their ability to operate over a wide range of flow rates and pump heads.Ĭentrifugal pumps basically consist of a stationary pump casing and an impeller mounted on a rotating shaft. Centrifugal pumps are the most common type of pumps found in DOE facilities.
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