Composition and Vibration Analysis of Centrifugal Pumps

A centrifugal pump works by using the rotation of the impeller to create a centrifugal motion in the water. Before starting the pump, the pump casing and suction pipe must be filled with water, then the motor is started, driving the pump shaft and impeller to rotate at high speed. The water is subjected to a centrifugal motion, thrown towards the outer edge of the impeller, and flows into the pressurized pipe of the water pump through the passage of the volute casing.

Composition of centrifugal pump structure

The basic structure of a centrifugal pump is composed of six parts: impeller, pump body, pump shaft, bearings, sealing ring, stuffing box.

The impeller is the core part of the centrifugal pump. It rotates at high speed and generates large power. The blades on the impeller play a major role. The impeller must undergo a static balance test before assembly. The inner and outer surfaces of the impeller are required to be smooth to reduce the friction loss of the water flow.

The pump body, also called the pump casing, is the main body of the water pump. It plays the role of support and fixation and is connected to the bracket for installing bearings.

The function of the pump shaft is to connect the coupling with the motor and transmit the torque of the motor to the impeller. Therefore, it is the main component for transmitting mechanical energy.

The sliding bearings use transparent oil as the lubricant. If there is too much oil, it will seep along the pump shaft. If there is too little oil, the bearing will overheat and cause accidents! The highest temperature of the bearing during the operation of the water pump is 85°C, which generally operates at around 60°C.

The mechanical seal ring is also called a leakage reduction ring.

The stuffing box is mainly composed of stuffing, water seal ring, stuffing cylinder, stuffing cover, and water seal pipe. The main function of the stuffing box is to seal the gap between the pump casing and the pump shaft, preventing the water inside the centrifugal pump from flowing outside and preventing the outside air from entering the pump, keeping the vacuum inside the water pump. When the pump shaft and the stuffing generate heat due to friction, water should be injected into the water seal ring through the water seal pipe to cool the stuffing and ensure the normal operation of the water pump. Therefore, it is particularly important to check the stuffing box during the operation and inspection of the water pump, and the stuffing should be replaced after running for about 600 hours.

Vibration analysis of centrifugal pump spare parts

Unbalance and misalignment of the rotor of the centrifugal pump spare parts. This problem accounts for a large proportion of the vibration problems in the centrifugal pump, about 80%. Factors causing unbalance of the centrifugal pump rotor: uneven material organization, unqualified part structure, resulting in eccentricity of the center of mass of the rotor and the centerline of the shaft to form unbalance. The correction of the unbalance of the centrifugal pump can be divided into two categories: static balance and dynamic balance, generally called single-plane balancing and double-plane balancing. The difference lies in the fact that single-plane balancing corrects the balance on one correction plane, while double-plane balancing corrects it on two correction planes.

Installation reasons. Loose foundation bolts and poor adjustment of the level. Before the centrifugal pump works, check whether the foundation bolts are loose and whether the installation of the pump is level. These factors can also cause vibration during the operation of the centrifugal pump.

The presence of foreign objects in the centrifugal pump spare parts. Before the mechanical seal types centrifugal pumps work, check the inside of the pumps, as there may be foreign objects inside the centrifugal pumps after long-term use, such as weeds in the water.

The internal cavitation perforation of the centrifugal pump caused by long-term use.

There are unreasonable design aspects of the centrifugal pump, such as the size and dimensions of parts. However, this situation is relatively rare. Before leaving the factory, the centrifugal pump will undergo multiple inspection processes in the workshop to ensure the qualification rate of the spare parts.