A volute is a curved funnel that increases in area as it approaches the discharge port. The volute of a

centrifugal pump Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are a sub-class of dynamic ...

is the casing that receives the

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

being pumped by the

impeller An impeller or impellor is a rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid. In pumps An impeller is a rotating component ...

, maintaining the velocity of the fluid through to the diffuser. As liquid exits the impeller it has high kinetic energy and the volute directs this flow through to the discharge. As the fluid travels along the volute it is joined by more and more fluid exiting the impeller but, as the cross sectional area of the volute increases, the velocity is maintained if the pump is running close to the design point. If the pump has a low flow rate then the velocity will decrease across the volute leading to a pressure rise causing a cross thrust across the impeller that we see as vibration. If the pump flow is higher than design the velocity will increase across the volute and the pressure will decrease according to the first law of thermodynamics. This will cause a side thrust in the opposite direction to that caused by low flow but the result is the same - vibration with resultant short bearing and seal life. The volute does not convert

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its accele ...

into

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

- that is done at the diffuser by reducing liquid velocity while increasing pressure. Plinthed pump, Gloucester Docks - geograph

The name "volute" is inspired by the resemblance of this kind of casing to the scroll-like part near the top of an ionic order column in

classical architecture Classical architecture usually denotes architecture which is more or less consciously derived from the principles of Greek and Roman architecture of classical antiquity, or sometimes even more specifically, from the works of the Roman architect V ...

, called a

volute A volute is a spiral, scroll-like ornament that forms the basis of the Ionic order, found in the capital of the Ionic column. It was later incorporated into Corinthian order and Composite column capitals. Four are normally to be found on an Ion ...

Split volute

In a split volute or double volute pump, the path along the volute is partitioned, providing two distinct discharge paths. The streams start out 180 degrees from each other, and merge by the time they reach the discharge port. This arrangement helps to balance the radial force on the bearings.

References

Fluid dynamics Pumps {{engineering-stub