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Volute
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Volute is considered a hydraulic component of pump. Hydraulic components are
those consisting of the wetted surface area of a pump, or those that are in
contact with the pumped liquid. These component  include the casing suction (or
suction bay area), the volute, and the crossover in the case of multistage pump.
In vertical lineshaft pumps, this will also include the suction bell and the
discharge nozzle head.

The purpose or function of a volute is to contain the liquid within the pressure
boundary of the casing, and control the flow of liquid from the impeller suction
bay area to the discharge side of the volute. The minimum metal thickness of
the volute should be sufficient to withstand the stress from the full shutoff
pressure of the pump and should include a corrosion allowance.

In low pressure pumps where the volute hoop stress is very low requiring small
metal thickness, the required metal thickness may be dictated by the required
minimum thickness to obtain commercial casting successfully as thin casting may
result in high rate of rejects.


Volute-related terms:

Single volute - a volute, or volute corebox, with only one lip, or one throat area.

Double volute - a volute, or volute corebox, with two lips, or two throat areas,
that are located in opposite sides of the volute. The term "double volute" should
not be confused with the term "double suction".

Base circle - a reference circle whose diameter typically corresponds to the
maximum impeller that fits the volute

Cutwater diameter
Volute lip
Volute throat area
Volute splitter
Volute corebox

Collector
Volute crossover
Short crossover
Long crossover
Intermediate crossover
Dump area

A-gap
B-gap
C-gap
Diffusion area
Diffusion angle
End-of-diffusion



Questions:

1. In pumps with double volute design is it mandatory for the two volute lips to be
located at exactly 180 degrees apart?

2. The volute throat area can be designed in different shapes - circular, square,
rectangular, or trapezoidal; which shape is found to give the most efficient
hydraulic performance?

The answers are discussed in the full version of this article.


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