What Are Magnetic Drive Pumps?

Magnetic drive pump is a new type of non-sealed pump that uses the principle of permanent magnet drive technology to achieve torque contactless transmission. There is no mechanical connection between the driving shaft and the driven shaft, and there is no need for a dynamic seal in the structure. Therefore, this type of pump has no seal and can achieve zero leakage. It is especially suitable for conveying flammable, explosive, volatile, toxic, and Corrosion and precious liquids, magnetic pumps are mostly used in situations where the pump can only be slightly leaked or not leaked, and high vacuum where mechanical seals are difficult to handle. In recent years, the pump has been widely used in petroleum, chemical, electroplating, pharmaceutical, food, paper selection, printing and dyeing industries. ^[1]

The magnetic gear pump is a positive displacement gear pump that realizes non-contact torque transmission through a magnetic actuator to replace the dynamic seal with a static seal. The pump starts with

Magnetically driven pumps use magnets to attract ferromagnetic materials and magnetic forces between magnets or magnetic fields. Non-ferromagnetic materials do not affect or rarely affect the magnitude of magnetic force, so they can pass through non-magnetic conductors (isolating sleeves) without contact. Characteristics of power transmission. The magnetic drive pump is mainly composed of a pump body, an impeller, a magnetic coupling, an isolation sleeve, and a motor. The motor is connected to the outer magnetic steel through a coupling. The impeller and the inner magnetic steel are integrated by the impeller nut and the pump inner shaft, and are installed in a sealed body composed of a pump body and an isolation sleeve. The electric motor drives the outer magnetic steel, and the outer magnetic steel drives the inner magnetic steel to rotate the impeller, so that the dynamic seal is replaced by a static seal to achieve a leak-free conveying medium. ^[2]

Connection by motor

(1) Direct-coupled structure The external magnetic rotor is driven by the motor shaft for active rotation. The prime mover uses a B35-connected direct-coupled motor. The advantage is that the pump has a compact structure and a small space. The disadvantage is that the disassembly and maintenance are relatively complicated. Usually applied to the case of small motor power.

(2) The non-directly coupled structure is also called a bearing bracket structure. The external magnetic rotor is driven by the drive shaft to actively rotate, and the drive shaft and the motor shaft are connected by a coupling. The advantage is that disassembly and maintenance are very simple and convenient, and the operation is stable. The disadvantage is the long axial dimension and large space volume. Mainly used in the case of large motor power. ^[3]

Leak-free principle

From the structural diagram of the magnetic pump (see Figure 2), it can be seen that the isolation sleeve component and the connected pump body form a completely closed shielded and sealed cavity. The rotor parts composed of impeller, pump shaft and internal magnetic rotor are completely enclosed in this shielded sealed cavity for the medium to be transported. The outer magnetic rotor is located on the outside of the shielded and sealed cavity, located in the air, and transmitted to the inner magnetic rotor and impeller located in the medium through the effect of the magnetic field in the space. Because the shielded seal cavity composed of stator components such as the isolation sleeve is only statically sealed, at the same time, the pump shaft that drives the impeller to do fluid work does not penetrate the shielded seal cavity, so there is no shaft seal. Therefore, the magnetic pump is a completely leak-free fluid conveying machine without a dynamic seal, but only a static seal.

Eddy current loss

In the magnetic pump, when the outer magnetic rotor drives the inner magnetic rotor to rotate synchronously, a rotating magnetic field is generated between the inner and outer magnetic rotors. The isolating sleeve in the middle of the inner and outer magnetic rotors is cutting magnetic lines of force relative to this rotating magnetic field. Therefore, if the isolating sleeve is made of a metal conductive material, it will inevitably generate an induced current on the surface of the isolating sleeve, that is, a magnetic eddy current. The energy loss caused by eddy current is called magnetic eddy current loss. Generally, the eddy current loss is expressed in the form of heat, which will reduce the overall machine efficiency by 1% to 7%. At the same time, it will increase the temperature of the insulation sleeve. Once the temperature at the insulation sleeve exceeds the maximum use temperature of the permanent magnet, it will affect the use of the permanent magnet. Therefore, in the design of the magnetic pump, the temperature of the isolating sleeve must be controlled to ensure the safe and reliable operation of the permanent magnet.

Cooling cycle system

Most of the magnetically driven pumps have a cooling cycle system, and there are two types of circulation modes.

(1) Internal circulation mode A high-pressure circulating medium is introduced in the part of the pump near the impeller outlet. Most of the high-pressure fluid passes through the narrow gap between the internal magnetic rotor and the isolation sleeve, flows through the central hole of the pump shaft or other channels, and returns to the pump. Sucking population. Another small part passes the thrust end face of the thrust bearing and the sliding bearing, and then passes through the lubricating oil groove of the sliding bearing, and then returns to the suction of the pump to complete the lubrication and cooling effect on the isolation sleeve, the sliding bearing and the thrust bearing.

(2) The external circulation method leads to a high-pressure circulating medium in the high-pressure area at the exit of the pump. After passing through external auxiliary equipment such as cooling and filtering, the high-pressure fluid enters the pump to complete the lubrication of the isolation sleeve, sliding bearing and thrust bearing. And cooling effect.

Generation and balance of axial force

The generation of axial force is mainly composed of the following parts: the axial force caused by the inconsistent pressure on the front and rear cover plates of the impeller, the axial force of the introduced high-pressure cooling circulating fluid acting on the internal magnetic rotor, and the impeller performing work on the medium The dynamic reaction force acting on the impeller at the time, and the axial force acting on the end face of the thrust bearing by the pump pressure of the conveyed medium.

As a result of the above axial force, a very large axial force is generated, which acts on the entire rotor component and points to the pump population, usually several thousand newtons, or even more than ten thousand newtons. Thrust bearings are not capable of withstanding such large axial forces. Therefore, in order to ensure that the thrust bearing can work for a long time, safely and stably, the axial force in the pump must be balanced.

There are many ways to balance axial force in magnetically driven pumps, one of which is a hydraulic self-balancing system for axial force in the pump. By changing the bearing area of the front and rear cover plates of the impeller, when the pressure generated by the impeller acts on the front and rear cover plates, a magnitude equal to or close to the impeller is generated, but it is opposite to the axial force acting on the entire rotor. Thereby, the axial forces in the pump are substantially balanced.

After the hydraulic self-balance of the axial force in the pump, the axial force on the thrust bearing can be controlled within a small range, and the specific pressure of the end face on the thrust bearing can also be controlled within a reasonable range.

Material selection

(1) Material of main flow components For large flow components such as pump body, impeller, and pump cover, their material selection is basically the same as that of ordinary pumps, such as: ZG230-450; ZG1Cr18Ni9; ZG0Cr18Ni12Mo2Ti; ZG00Cr17Ni14Mo2 and other cast steel and stainless steel castings as well as

In normal use of the magnetic pump, as long as it is correctly operated according to the instructions of the operating regulations, the magnetic pump can achieve the purpose of long life and long cycle operation. Due to the limitation of its own structural characteristics, the magnetic pump must pay attention to the following matters during use.

(1) Dry operation is strictly prohibited;

(2) Thoroughly remove rust and solid foreign matter in the device;

(3) The air in the pump must be removed before the pump runs;

(4) No-flow operation time shall not exceed 60s;

(5) No continuous continuous operation;

(6) During operation, if abnormal sounds or vibrations are found, the cause must be quickly investigated to eliminate the fault;

(7) It should not run when it is less than the minimum flow;

(8) The normal working state of the pump must be within the range of performance parameters required by the contract, otherwise it will affect the axial force in the pump;

(9) Normal temperature magnetic pump (neodymium iron boron magnetic material) is strictly prohibited from "high temperature" scanning.