First, the working principle of centrifugal pump
The working principle of centrifugal pump is: relying on the high-speed rotating impeller, the liquid obtains energy under the action of inertial centrifugal force to increase the pressure . Before the pump works, the pump body and the water inlet pipe must be filled with water to prevent cavitation. When the impeller rotates rapidly, the blades make the water 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, the central part of the impeller forms a vacuum area. The water of the water source is pressed into the water inlet pipe through the pipe network under the action of atmospheric pressure (or water pressure). This cycle is endless, and continuous pumping can be achieved. It is worth mentioning here that the centrifugal pump must be filled with water before starting the pump, otherwise it will cause the pump body to heat up, vibrate, reduce the water output, and cause damage to the pump (referred to as “cavitation”). Cause equipment accident! The so-called cavitation means: when the centrifugal pump is started, if there is air in the pump, due to the low density of the air, the centrifugal force generated after rotation is very small, so the low pressure formed in the central area of the impeller is not enough to lower the liquid level below the pump inlet. The phenomenon that the liquid is sucked into the pump and cannot be transported.
Second, the main structure of the centrifugal pump
The basic structure of the centrifugal pump is composed of seven parts, namely: impeller, pump body, pump shaft , Bearings, sealing rings, stuffing boxes, axial force balance device.
1. The impeller is the core part of the centrifugal pump. It has high speed and high output, and the blades on the impeller play a major role. The impeller must pass a static balance test before assembly. The inner and outer surfaces on the impeller are required to be smooth to reduce the frictional loss of the water flow.
2. The pump body is also called the pump casing, which is the main body of the water pump. It plays the role of supporting and fixing, and is connected with the bracket on which the bearing is installed.
3. The function of the pump shaft is to connect the motor with the coupling and transmit the torque of the motor to the impeller, so it is the main component for transmitting mechanical energy.
4. The bearing is a component that is sleeved on the pump shaft to support the pump shaft. There are two kinds of rolling bearings and sliding bearings. Sliding bearings use transparent oil as lubricant, add oil to the oil level line.
5. The sealing ring is also called the leakage reducing ring.
6. The stuffing box is mainly composed of packing, water sealing ring, packing cylinder, packing gland and water sealing tube. The function of the stuffing box is mainly to close the gap between the pump casing and the pump shaft, so that the water flow in the pump does not flow to the outside and the outside air does not enter the pump. Always maintain a vacuum inside the pump! When the friction between the pump shaft and the packing generates heat, it is necessary to rely on the water seal tube to hold the water into the water seal ring to cool the packing! Keep the pump running properly. Therefore, special attention should be paid to the inspection of the stuffing box during the circuit inspection process of the pump! The packing should be replaced after about 600 hours of operation.
7. Axial force balance device. During the operation of the centrifugal pump, since the liquid enters the impeller under low pressure and flows out under high pressure, the pressure on both sides of the impeller is unequal, resulting in a directional pressure. The axial thrust in the inlet direction will cause axial movement of the rotor, resulting in wear and vibration, so an axial thrust bearing should be installed to balance the axial force.
