How does the spiral-shaped outlet of a volute centrifugal pump increase pressure?

In a volute centrifugal pump, the spiral-shaped casing plays a critical role in converting the kinetic energy of the fluid into pressure energy.12

As the impeller rotates at high speed, it imparts a high velocity to the fluid, throwing it radially outward against the casing. The pump's outlet is designed to widen progressively in a spiral fashion. According to the principles of fluid dynamics, as the cross-sectional area of this channel increases, the velocity of the fluid is reduced.123

This reduction in velocity (kinetic energy) is converted into an increase in pressure head, allowing the pump to deliver a continuous flow of fluid at high pressure. This process is a practical application of the relationship between velocity and pressure in moving fluids, often described by Bernoulli’s theorem.123