The Benefits of Using Double Volutes Housing

Curved funnel that increases in area as it approaches the discharge port

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A volute is a curved funnel that increases in area as it approaches the discharge port.[1] The volute of a centrifugal pump is the casing that receives the fluid being pumped by the impeller, 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 into pressure &#; that is done at the diffuser by reducing liquid velocity while increasing pressure.

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, called a volute.

Split volute

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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.[2]

References

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A pump casing is often referred to as a volute. A volute is a spiral-like geometry with an increasing through-flow area, reducing the velocity of the fluid and increasing the static pressure. The fluid exiting the impeller is then diffused towards the casing discharge nozzle. These volute casings come in two different types: single volute and double volute.

The casing is the major stationary component of the pump and mainly provides two functions:

Single Volute Casing

In a single volute casing, the impeller discharges into one volute that wraps completely around the impeller. This type of casing features one cutwater that directs the flow of the liquid towards the discharge of the pump.

Double Volute Casing

Double volute casings have two cutwaters located 180 degrees apart from each other. Normally a double volute pump can be identified simply by looking down the discharge flange: a noticeable vane is located inside the nozzle that divides the inner diameter of the discharge nozzle.

The main advantage of a double volute over a single volute is the balancing of radial loads on the impeller, as the double cutwater construction leads to a more equal pressure distribution in the volute. Minimizing the radial load on the bearings over the full operating range can have a significant impact on the lifetime of a pump, since bearing failures are the second most common reason for pump failures. However, a double volute adds additional hydraulic resistance.

In addition to single and double volute casings, another type of pump casing exists: the diffuser casing.

Volute (pump) - Wikipedia

Single and double volute casing - Rodelta Pumps International