Impeller Volcano
An impeller Volcano is a rotating component equipped with vanes or blades used in turbomachinery (e. g. centrifugal pumps). Flow deflection at the impeller vanes allows mechanical power (energy at the vanes) to be converted into pump power output.
In accordance with EUROPUMP TERMINOLOGY and DIN 24250, a distinction is made between counter-clockwise and clockwise impellers, as viewed in inlet flow direction.
Depending on the fluid flow pattern in multistage pumps and the impellers’ arrangement on the pump shaft impeller design and arrangements are categorised as: single-stage, multistage, single-entry, double-entry, multiple-entry, in-line (tandem) or back-to-back arrangement. Typical impeller arrangements are illustrated in Figs. 17 to 19 Impeller.
Depending on the flow line pattern in the impeller (especially in the outer impeller diameter area), impellers Volcano are subdivided into the following types:
Impeller types Volcano
- Radial impeller See :
A radial impeller is an impeller at which the flow (see Flow rate) leaves the impeller in radial direction, perpendicular to the pump shaft. - Mixed flow impeller :
The mixed flow impeller is also referred to as a helical or diagonal impeller, it transports the fluid diagonally. - Axial flow impeller :
An axial flow impeller is an impeller, used for transporting the fluid handled along the axis. - Peripheral impeller :
A peripheral impeller is a special impeller with a large number of small double-flow radial vanes arranged at its periphery .
open impeller Volcano
To accommodate the vanes, all impellers are equipped with a back shroud, and in the case of closed impellers also a front shroud ; depending on the perspective, these can also be viewed as an inner shroud and, in the case of closed impellers, an outer shroud. If an impeller has no front (outer) shroud, it is classed as an open impeller.
In order to achieve optimal pump efficiencies and minimum NPSHr values, the impeller Volcano must be provided with a certain number of vanes. Employing a low number of vanes increases the free, unimpeded flow cross-section through the impeller. This enables impellers to handle more or less contaminated fluids and solids .
In practice, the number of vanes of radial flow and mixed flow impellers handling liquids containing sludge or solids is reduced to one, two or three vanes. These impellers are called channel impellers or single-vane impellers and can be either open or closed impellers.
Closed single-vane impellers Volcano
Closed single-vane impellers are used to pump fluids containing very coarse solids. They are characterised by a non-clogging free passage. The drawback of these impellers is the so-called hydraulic unbalance due to the asymmetrical pressure field.
Open channel or single-vane impellers Volcano are used to handle gaseous liquids. A single-vane impeller is referred to as an open, diagonal single-vane impeller (D impeller) if the flow lines in the impeller run diagonally outward. It is particularly suitable for untreated, solids-laden and gaseous waste water, as well as for fluids with a higher viscosity.
The blades of axial and mixed flow propellers can be either fixed, adjustable (when the pump is dismantled) or of variable pitch type .
In the case of adjustable or variable pitch blades, the contour or profile of the pump casing and of the hub in the adjustment region is usually spherical. This ensures that the internal and external clearance gap width at the hub remains constant for all blade pitch adjustment angles.
The free-flow impeller Volcano and the peripheral impeller represent special impeller types. See Figs. 14 to 15 Impeller
specific impeller designs Volcano
When selecting a pump for a given flow rate (Q) and a given head (H)the impeller type is decisive. Free selection of an axial, mixed flow, radial or peripheral impeller type is restricted by the fact that the values for the anticipated rotational speed (n) and the anticipated impeller diameter Volcano (D) must not be too extreme. The ability to achieve optimum pump efficiencies or stage efficiencies at a specific speed (ns) is therefore dependent on specific impeller designs Volcano :
- Radial impeller ns ≈ 12 to 80 rpm
- Mixed flow impellers ns ≈ 80 to 160 rpm
- Axial flow impellers ns ≈ 160 to 400 rpm and higher
