What Is an Axial Force?

Axial force refers to the reverse tensile force or pressure on a certain cross section of a structure or component caused by the action. When the reverse tensile force is located at the centroid of the section, it is called axial force.

It can compete with the gravity of the earth, that is, it can make the object more stable.

The axial force is

The axial force of the water pump is generated when the water pump rotates. For the cause of the axial force, many scholars have studied it in the past to improve the ability of the water pump to operate safely and reliably. The research shows that the reasons for the axial force of the pump are divided into the following aspects:

(1) Unbalanced liquid pressure before and after the pump impeller. When the water pump works, the impeller drives the liquid to rotate. In this process, the liquid passes through the impeller of the rotating machine before and after, and the area of the liquid that acts on the suction inlet of the impeller and the back of the impeller is not equal. At the same time, the part of the suction inlet of the rotating machine is low pressure and the back is high pressure. As a result of the pressure difference between the front and back of the impeller, a pressure difference will be formed between the front wheel cover and the rear disk of the impeller, which acts on the front cover and the rear cover The fluid pressures cannot balance each other, creating an axial force.

(2) The axial component of the liquid momentum changes. After the liquid flows in from the impeller suction inlet and flows out from the impeller outlet, the momentum component in the direction of the axial force of the liquid will change. The reason is that the speed of the liquid acting on the front and back of the impeller will not only change. The direction has also changed a lot. According to the analysis of the momentum theorem, it is found that during the liquid passing through the impeller, due to the change in the axial component of the liquid momentum, an impulse is generated in the axial direction, which is also called the kinetic reaction force.

(3) The reason for the axial force is different for different pump bodies. The weight of the internal rotor of the vertical pump will also become part of the axial force during the operation of the pump; the gravity of the rotor inside the horizontal pump will not generate axial force on the pump.

Many years of practice show that the problem of the axial force balance of the pump has become the key to the universal application of the pump. No matter in the structural design of the pump or in practical application, it is necessary to balance the axial force as much as possible to provide a guarantee for the reliable operation of the pump. The device for balancing the axial force of the pump is designed according to the magnitude of the axial force. Most of the axial force is balanced by the balancing device, and a small part of the axial force is borne by mechanical devices such as thrust bearings inside the pump. In this way, the effect of axial force is eliminated, and it will not pose a threat to the safe operation of the pump ^[1]

Canned motor pump is a kind of centrifugal pump with no shaft seal, absolutely no leakage, compact structure, small size, light weight, no cooling fan and low noise. It is widely used in important fields such as petrochemical industry, aerospace, defense industry, environmental protection, etc. Used to transport flammable, explosive, volatile, corrosive, highly toxic, precious and other media. However, due to its own characteristics, the axial force balance of the canned pump has become a key factor affecting the life and efficiency of the canned pump. Practice shows that many of the failures of canned pumps are due to the excessive axial force and failure to balance graphite bearings. Therefore, it is very important to research the new method of axial force balance of the canned pump to reduce or eliminate the damage of the axial force as much as possible.

By analyzing the characteristics of the axial force of the canned pump, a secondary impeller is designed to circulate the coolant in the cooling circuit and generate an axial force that is equal to the combined force of the axial force generated by the main impeller and the gravity of the rotor. The balancing method is innovative, the design is reasonable and feasible. At the same time, without the need for additional power, the additional auxiliary impeller drives the cooling circulating liquid to work, achieving a good cooling effect and achieving system energy saving. This method is used to balance the axial force of the canned pump. The calculation results of the residual axial force are basically consistent with the experimental measurement results, and they are less than the values specified by the manufacturer. The residual axial force can be basically eliminated, and the bearing load can be reduced and extended The service life of the bearing is achieved, and the safe and reliable operation of the canned pump is realized. The balance method is reliable, the calculation process is correct, and has important reference and application value ^[2]

(1) Numerical simulation can accurately predict the performance and axial force of deep-well centrifugal pumps, and it can provide more reliable reference data in the working flow range, but the numerical simulation prediction value is relatively large when it deviates from the working flow range of the pump.

(2) When measuring axial force, the value should be reset to zero after a period of trial operation, so that the weight of all rotors falls on the motor shaft, and ensure that the measured value is the axial force experienced by the impeller during rotation the size of.

(3) The axial force components on the front and rear covers are the main component of the axial force of the impeller. Reducing the diameter of the rear cover can effectively balance some of the axial forces.

(4) The axial force of the deep well centrifugal pump gradually decreases with the increase of the flow rate. In practical applications, it should be avoided as long as possible to run the pump at a small flow rate for a long time ^[3] .