Marine centrifugal pump is a type of pump that uses the impeller to rotate at a constant speed in the pump casing, causing the liquid in the impeller to rotate together with the impeller, generating centrifugal inertia force and flying away from the impeller, thereby achieving the suction and discharge of liquid.

From the perspective of structure and operation mode, centrifugal pumps and rotary pumps are basically the same, with the difference being that the rotor impeller of centrifugal pumps does not have metal friction; In terms of working principle, centrifugal pumps are completely different from rotary pumps. The suction and discharge of rotary pumps rely on volume changes, while centrifugal pumps rely on the centrifugal force acting on the liquid during the rotation of the impeller, which creates a pressure difference between the center of the impeller and the outside of the pump chamber, and can suction and discharge liquid.

Centrifugal pumps are mainly composed of impeller, pump casing, pump cover, pump shaft, mechanical seal and other main components. The impeller is installed on the shaft and rotates together with the shaft. The outer edge of the impeller is surrounded by a spiral shaped volute chamber on the pump casing. There is a suction pipe on the pump cover and a discharge pipe on the pump casing. The impeller consists of front and rear side plates and a curved blade connected in the middle. The rotating shaft and pump casing are sealed with a machine seal.

When a marine centrifugal pump is working, the pump chamber is first filled with liquid. When the pump shaft drives the impeller to rotate together, the impeller blades push the liquid inside the impeller to rotate together. The liquid generates centrifugal force when it rotates at high speed and moves from the center of the impeller to the volute chamber of the pump casing. The liquid pressure inside the chamber increases accordingly and is discharged through the discharge outlet. The liquid pressure at the center of the impeller decreases, creating a vacuum that continuously sucks in the liquid, thus achieving the purpose of transporting the liquid.

During the operation of a centrifugal pump, the liquid pressure changes along the radius of the impeller: the reason for the increase in pressure of the liquid on the outside of the pump casing is due to the mechanical energy transmitted from the rotation of the impeller to the liquid, which becomes the result of the pressure energy of the liquid. Under the action of centrifugal force, the liquid is thrown towards the outer diameter of the impeller, forcing the amount of liquid at the center of the impeller to decrease. The pressure drops to form a vacuum, which is lower than the external atmospheric pressure. Under this pressure difference, the liquid is continuously sucked into the center of the impeller. If the pressure at the outer edge of the impeller is greater than the outlet pressure of the pump, the liquid is continuously discharged through the discharge pipe. If the pressure is equal to the outlet pressure of the pump, the centrifugal pump will idle and not discharge liquid outward. But the pump will not be damaged, which is also one of the differences between centrifugal pumps and other positive displacement pumps.

The magnitude of centrifugal force obtained by a liquid in a centrifugal pump is not only related to the diameter and speed of the impeller, but also to the density of the liquid. When the density of the liquid is as low as air, the centrifugal force obtained by the rotation of the impeller is too small, forcing the pressure at the center of the impeller to not reach vacuum. The liquid level below the pump cannot enter the pump under the pressure difference, and the pump cannot work. This is the main reason why centrifugal pumps are different from other volumetric pumps in that they do not have dry suction. Therefore, before starting the centrifugal pump, various methods need to be used to fill the pump chamber with liquid in advance to eliminate the gas inside the pump before starting the pump to enter normal operation. This process is habitually called the "water intake" process of the centrifugal pump.