Impeller types can be radial, mixed flow, axial and peripheral and are selected on the basis of the pump design and the application. The number of vanes will affect the efficiency; in general more vanes are more efficient.
Semi closed impellers
Closed impellers
Open impellers
Vanes are attached to the central hub, without any form, sidewall, or shroud, and are mounted directly onto a shaft. Open impellers are structurally weak and require higher NPSHR values. The impeller to volute or back plate clearance must be adjusted when the pump is at operating temperature and all axial thermal growth has occurred.
They are typically used in small-diameter, inexpensive pumps and pumps handling suspended solids. They are more sensitive to wear than closed impellers, thus their efficiency deteriorates rapidly in erosive service. Efficiency can be maintained through impeller clearance adjustment.
They are typically used in small-diameter, inexpensive pumps and pumps handling suspended solids. They are more sensitive to wear than closed impellers, thus their efficiency deteriorates rapidly in erosive service. Efficiency can be maintained through impeller clearance adjustment.
The vanes are free on one side and enclosed on the other. This type of impeller incorporates a back wall (shroud) that serves to stiffen the vanes and adds mechanical strength. They are used in medium-diameter pumps and with liquids containing small amounts of suspended solids. They offer higher efficiencies and lower NPSHR than open impellers. It is important that a small clearance or gap exists between the impeller vanes and the housing. If the clearance is too large, slippage and recirculation will occur, which in turn results in reduced efficiency and positive heat buildup.
Closed impellers
The vanes are located between the two discs, all in a single casting. The closed impeller has both a back and front wall for maximum strength. They are used in large pumps with high efficiencies and low NPSHR. They can operate in suspended-solids service without clogging but will exhibit high wear rates. Good for volatile and explosive fluids because the close clearance wear rings are the parts that will contact if the shaft displaces from its center line. The closed-impeller type is the most widely used type of impeller for centrifugal pumps handling clear liquids. They rely on close-clearance wear rings on the impeller and on the pump housing. The wear rings separate the inlet pressure from the pressure within the pump, reduce axial loads, and help maintain pump efficiency. Closed impellers are high-efficiency design for pumping water and other liquids at higher head pressures.