Double volute casings
Double volute casings were introduced to eliminate the radial thrust problems inherent in the single volute design. Test measurements do, however, indicate that while the radial forces in a double volute are greatly reduced, they are not completely eliminated.
In a double volute casing, the flow is divided into two equal streams with two cut-waters set 180 degrees apart. The total throat area of the two volutes is identical to that which would be used on a comparable single volute design. As such, a double volute casing design is actually a single volute with a splitter vane extending 180 degrees from what would be the single volute throat welling into the diffuser section, creating two equal scrolls, each with constant velocity at the pump BEP. The two volute sections still generate non-uniform pressures around the impeller at off-BEP flow rates but tend to cancel each other out to a large extent, as shown by the resulting lower radial loads. This is the main reason for using a double volute casing.
The hydraulic performance of double volute pumps is nearly as good as that of single volute pumps. Tests indicate that a double volute pump will be approximately one to one-and-a-half points less efficient at the BEP but will be approximately two points more efficient on either side of the BEP than with a comparable single volute pump. This means that a double volute casing will produce a slightly higher efficiency over the full range of the head-capacity curve than a single volute.
Double volutes are most common with larger-axial, split-case, double-suction impeller pumps, which also have lower-axial impeller loads. Double volute casings should not be used in smaller, low-flow pumps (below about 400 gpm). Since larger pumps are better candidates for double volutes, they should normally be selected for such service when available and if the application permits. The splitter vane in a double volute can cause blockage problems when handling solids, such as in wastewater applications, which would preclude their use in these applications.
Except that, there are other types of Pump Casing like Valve Parts Investment Casting, Pump Parts Investment Casting, Pump Cover Casting, Pump Impeller Casting, Machinery Parts Investment Casting and so on used widely in the industrial production.