When the centrifugal pump is running, it produces a large force on its rotor. Because the direction of the force is parallel to the axis of the centrifugal pump shaft, it is called the axial force. Whether it is a single-stage pump or a multi-stage pump, the axial force imbalance is often encountered in daily production, so the effective relief and elimination of the axial direction can prolong the service life of the equipment, thereby improving the economic operation ability of the equipment.
Axial force elimination method of single-stage centrifugal pump
①There is a balance hole on the wheel. The purpose is to equalize the pressure on both sides of the impeller, so as to balance the axial force, drill several small holes (called balance holes) symmetrically on the impeller disc near the hub, and set them on the pump casing and disc The sealing ring greatly reduces the pressure difference between the two sides of the impeller and reduces the axial force. This method is simple and reliable, but there is a part of the liquid returning to the impeller to suck the population, which reduces the efficiency of the pump. This method is widely used in single-stage, single-suction centrifugal pumps.
②Double suction impeller is used. It uses the structural characteristics of the impeller itself to achieve its own balance. Because the double-suction impeller is symmetrical on both sides, there is no axial force in theory. However, due to the difference in manufacturing quality and liquid flow on both sides of the impeller, it is impossible to make the axial force complete. balance.
③Radial ribs are set on the impeller. Radial ribs are arranged on the outer side of the impeller disk to balance the axial force. After the radial ribs are installed, the liquid on the high-pressure side of the impeller is driven by the radial ribs and rotates at a speed close to the speed of the impeller. Under the action of centrifugal force, The liquid pressure in the cavity is reduced, so that the axial force on both sides of the impeller is balanced. The disadvantage is that there is additional power loss. Generally, 4 radial ribs are used in small pumps, and 6 radial ribs are used in large pumps.
④Set the thrust bearing. When the above method cannot completely eliminate the axial force, the method of installing a thrust bearing should be used to withstand the remaining axial force.
Axial force elimination method of multistage centrifugal pump
For multi-stage centrifugal pumps, the outlet pressure is generally much greater than the inlet pressure, so it is especially important to use a balance force to eliminate the axial force. As for how to eliminate the axial force, please see the following two points:
①The pump body is equipped with a balance tube, and the high-pressure end near Lun Yi on the outside of the impeller disc is connected with the suction end of the centrifugal pump with a pipe to balance the pressure on both sides of the impeller and eliminate the axial force. The advantages and disadvantages of this method are similar to the balanced hole method. Some centrifugal pumps are equipped with a balance pipe and a balance hole at the same time, which can get a better balance effect.
②The impellers are arranged symmetrically. Two impellers, back to back or face to face, are mounted on a shaft, so that the axial forces generated by each two opposite impellers during operation cancel each other.
③The balance drum device is adopted, and a balance drum that rotates with the shaft is installed behind the last stage impeller of the segmented multistage centrifugal pump.
④The balance disc device is adopted. Behind the last stage impeller of the segmented multi-stage centrifugal pump, a balance disc that rotates with the shaft and a replaceable balance seat are embedded in the pump casing.
⑤Using a balance drum and balance plate combined device. The feature of this device is that 50% -80% of the axial force is balanced by the balance drum, and the remaining axial force is then balanced by the balance plate.
