Axial force refers to the reverse tension or pressure on a normal section of the structure or component caused by the actionCentroidIs called the axial force.
It can counter the gravity of the earth, that is, it can make the object more stable.topThe bicycle moves on this principle.When he leans in one direction, this balance will be broken, so a force like this direction will be generated.The greater the tilt angle, the greater the force.GermanynaziDeveloped during World War IIUFOThis is the basic principle for taking off and changing direction.
Causes of axial force of water pump
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The axial force of the pump is generated with the rotation of the pump. Many scholars have studied the causes of the axial force through the ages to improve the ability of the pump to operate safely and reliably.The research shows that the causes of the axial force of the pump can be divided into the following aspects:
（1）Pump impellerThe front and rear fluid pressures are unbalanced.When the water pump is working, the impeller drives the liquid to rotate. In this process, the area of the liquid acting on the suction inlet of the impeller before and after passing the impeller of the rotating machine is not equal to the area of the liquid acting on the back of the impeller.At the same time, the suction port of the impeller of the rotating machine is low pressure, and the back is high pressure. In this way, due to the different air pressure before and after the impeller, a pressure difference will be formed between the front cover and the rear disc of the impeller. The liquid pressure acting on the front cover and the rear cover cannot balance each other, producing an axial force.
(2) The axial component of liquid momentum changes.The momentum component in the axial force direction of the liquid will change during the process of liquid flowing in from the suction inlet of the impeller and flowing out from the outlet of the impeller. The reason is that the speed of the liquid acting before and after the impeller will not only change, but also the direction of the speed.According to the momentum theorem, when the liquid passes through the impeller, due to the change of the liquid momentum in the axial component, an impulse, also known as dynamic reaction force, is generated in the axial direction.
(3) The causes of axial force are different for different pump bodies.The weight of the internal rotor of the vertical pump will also become a part of the axial force during the operation of the pump;The rotor gravity inside the horizontal pump will not produce axial force on the pump.
Years of practice has shown that the balance of pump axial force has become the key to the general application of pumps.Whether in the structural design of the pump or in practical application, it is necessary to balance the axial force as much as possible to ensure the reliable operation of the pump.The device for balancing the axial force of the pump is designed according to the size of the axial force. Most of the axial force is balanced by the balancing device, and a small part of the axial force is balanced by the internalThrust bearingAnd other mechanical devices, so that the effect of axial force is eliminated, and there will be no threat to the safe operation of the pump[1]。
A new method of axial force balance for canned motor pump
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As a kind of centrifugal pump without shaft seal, absolute leakage, compact structure, small size, light weight, no cooling fan, and low noise, canned motor pump is widely used in important fields such as petrochemical industry, aerospace, national defense and military industry, environmental protection, and is used to transport flammable, explosive, volatile, corrosive, highly toxic, valuable and other media.However, due to its own characteristics, the axial force balance of canned motor pumps has become a key factor affecting the service life and efficiency of canned motor pumps.Practice shows that many failures of canned motor pumps are caused by too large axial force and poor balanceGraphite bearingDamage.Therefore, it is particularly important to study the new method of axial force balance of canned motor pump to reduce or eliminate the damage of axial force as far as possible.
Through the analysis of the characteristics of the axial force of the canned motor pump, a secondary impeller is designed to drive the coolant to circulate in the cooling circuit and generate an axial force with the same magnitude and opposite direction as the axial force generated by the main impeller and the rotor gravity. The balance method is innovative, and the design is reasonable and feasible.At the same time, without external power, the additional auxiliary impeller drives the cooling circulating liquid to work, achieving good cooling effect and realizing system energy saving.Using this method to balance the axial force of canned motor pump, the calculation results of residual axial force are basically consistent with the test measurement results, and both are less than the specified value of the manufacturer, which can basically eliminate the residual axial force, reduce the load of the bearing, extend the service life of the bearing, and realize the safe and reliable operation of canned motor pump.The balance method is reliable, the calculation process is correct, and has important reference and application value[2]。
epilogue
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(1) Numerical simulation can accurately predict the performance and axial force of deep well centrifugal pump, and can provide more reliable reference data in the working flow range, but the error of numerical simulation prediction value is relatively large when it deviates from the working flow range of the pump.
(2) When measuring the axial force, reset the value 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 size of the axial force applied to the impeller during rotation.
(3) The axial force component on the front and rear cover plates is the main part of the axial force of the impeller. Reducing the diameter of the rear cover plate can effectively balance the axial force of some parts.
(4) The axial force of deep well centrifugal pump gradually decreases with the increase of flow rate. In practical application, the pump should be avoided from running at low flow rate for a long time[3]。
