Volute (pump)

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

As liquid exits the impeller it has high kinetic energy and the volute directs this flow through to the discharge.

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.

The streams start out 180 degrees from each other, and merge by the time they reach the discharge port.