Factors Affecting The Efficiency Of Centrifugal Pump Units

Jan 20, 2025

The working principle of a centrifugal pump is to pump the medium through the centrifugal force generated by the high-speed rotation of the impeller.
Before the water pump starts working, the pump body and inlet pipe must be filled with water to prevent cavitation. When the impeller rolls rapidly, the blades cause the water to rotate quickly, and the rotating water flies away from the impeller under the action of centrifugal force. After the water in the pump is thrown out, a vacuum area is formed in the central part of the impeller. Water is pressurized into the inlet pipe through the pipeline network under the action of atmospheric pressure (or water pressure). This cycle can achieve continuous pumping.
It is worth mentioning that before starting the centrifugal pump, it is necessary to fill the pump casing with water, otherwise it will cause the pump body to overheat, shock, reduce the water output, and damage the pump (referred to as "cavitation"), resulting in equipment accidents!
The so-called cavitation refers to the phenomenon that when a centrifugal pump is started, if there is air inside the pump, due to the low density of the air, the centrifugal force generated after rotation is very small. Therefore, the low pressure formed in the central area of the impeller is not enough to suck the liquid below the pump inlet into the pump, and the fluid cannot be transported.

The efficiency of a centrifugal pump is the product of mechanical, volumetric, and hydraulic efficiencies. The efficiency of the pump unit is the product of the pump efficiency and the motor efficiency. The main factors causing low efficiency of centrifugal pump units are as follows.

The efficiency of the pump itself is the most fundamental impact. Under the same working conditions, the efficiency of pumps may differ by more than 15%.

2. The operating conditions of centrifugal pumps are lower than their rated conditions, resulting in low pump efficiency and high energy consumption.

3. The efficiency of the motor remains basically unchanged during operation. Therefore, choosing a high-efficiency motor is crucial.

The impact of mechanical efficiency is mainly related to design and manufacturing quality. After the pump is selected, the impact of later treatment is relatively small.

5. Hydraulic losses include hydraulic friction and local resistance losses. After running for a certain period of time, centrifugal pumps inevitably cause surface wear on components such as impellers and guide vanes, increase hydraulic losses, and decrease hydraulic efficiency.

6. The volume loss of centrifugal pumps, also known as leakage loss, includes three types of leakage losses: impeller sealing rings, interstage, and axial force balancing mechanisms. The level of volumetric efficiency is not only related to design and manufacturing, but also to later management. After running continuously for a certain period of time, due to friction between various components, the clearance increases and the volumetric efficiency decreases.

7. Centrifugal pump vacuum and idle due to blockage of filter cylinder, pipeline intake, and other reasons.

8. Before starting the pump, employees do not pay attention to the preparatory work before starting the centrifugal pump. The basic operating procedures such as warm-up pump, disc pump, and infusion pump are not thoroughly executed, which often causes cavitation of the pump, resulting in high pump noise, vibration, and low pump efficiency.