A centrifugal pump spins an impeller that throws water outward, turning speed into pressure. Use the buttons to look inside and follow the water from the suction inlet to the discharge outlet.
A centrifugal pump is a machine that moves liquid by spinning it. At its heart is an impeller — a disc with curved vanes — turning fast inside a casing. Water enters at the centre, is flung outward, and leaves through an outlet. Unlike a piston pump, it keeps up a smooth, continuous flow rather than pushing in pulses.
From the outside it is just a round metal housing with a pipe in and a pipe out. Everything that matters is hidden inside, so opening the casing shows how the spinning impeller and the spiral volute work together to move water and build pressure.
As the impeller spins, it lowers the pressure at its centre, called the eye. Because the pressure there is lower than in the suction pipe, water is pushed in by the surrounding atmospheric pressure — the pump does not pull it.
Curved vanes on the impeller grab the water and throw it outward. Spinning always speeds a mass up as it moves away from the centre, so the water leaves the impeller much faster than it entered — the impeller adds speed, not pressure.
The fast water leaves the impeller and flows into the volute, the spiral passage around it. The passage gets steadily wider, so the water slows down, and the energy it gives up as speed is converted into pressure. That is where the pump's pushing power is actually made.
Now under pressure, the water is guided out through the discharge outlet and into the pipework. The wider the volute and the slower the exit, the higher the pressure it can build.
A motor turns the impeller through a shaft. A bearing supports the spinning shaft, and a mechanical seal stops water leaking out where the shaft passes through the stationary casing.
No. The spinning impeller merely lowers the pressure at the inlet, and the surrounding atmospheric pressure then pushes the water in. That is why a centrifugal pump needs liquid at its inlet and usually has to be primed.
The volute. The impeller adds speed to the water, and the widening spiral passage slows that fast flow down and converts the lost speed into pressure on the way to the discharge.
Because it moves liquid by spinning it, not by gripping it like a piston. If the casing is full of air, the impeller cannot lower the pressure enough to draw water in, and running dry can damage the seal.
When the local pressure falls below the liquid's vapour pressure, tiny bubbles form in the water. They collapse violently against the impeller, eroding the metal and losing performance — so a pump must never run with too little pressure at its inlet.
It seals the gap where the turning shaft passes through the fixed casing, so water cannot leak out and air cannot be drawn in.