AS-C451 Customized Dual Cartridge Mechanical Seal

Background Knowledge：

Discussion on the installation and commissioning of mechanical seals of large submersible axial flow pumps （1）
This article describes how to improve the pass rate of the pump shaft seal（mechanical seal） air tightness test by strictly controlling the perpendicularity between the stationary seat end face of the mechanical seal and the shaft based on practical experience in the installation and maintenance of submersible pumps, thereby ensuring the reliability of the motor insulation and oil chamber seal（mechanical seal） and saving money.

I.Main issues
A pump station in China is equipped with a 10kv, 1300QZ-100-355 high-pressure submersible axial flow pump. Each pump has a single flow rate of 5m3/s and an impeller diameter of 1.3m. With the passage of time and the increase in frequency of use, problems such as a year-on-year increase in the operating temperature of the bearings and a decrease in the insulation of the supporting motors have gradually been exposed. After disassembly and inspection, it was found that:
(1)There is moisture inside the motor. (2) The No. 32 mechanical oil in the bearing cavity shows emulsification and precipitation. (3) The metal structure of the mechanical seal has rust spots, the spring is corroded, the friction surfaces of friction pairs of the mechanical seal are eccentrically worn, and the rotary face auxiliary seal of the mechanical seal (i.e., the O-type rubber ring) has been deformed and worn.

II.Analysis
After disassembly and inspection, it was found that the compensation ring of the oil seal (i.e., the mechanical seal of the motor cavity) was over-pressured, and the rotary face could not move flexibly on the pump shaft, resulting in greater wear of the friction pairs of the mechanical seal, and no compensation for displacement after wear. The oil in the oil chamber has been emulsified and deteriorated, causing impurity particles to penetrate into the friction pair of the oil seal. The lubrication conditions are poor, the temperature rises during operation, aggravates wear, and the mechanical seal gradually fails. The sealing performance of the water seal (that is, the mechanical seal outside the oil chamber that is in contact with water) decreases. Due to the sudden start and stop of the water pump and the rapid changes in the tide level of the outside river, the operating conditions change drastically, resulting in large pressure fluctuations. The river water containing a large amount of mud and sand penetrates the water seal under the action of pressure and enters the oil chamber. In addition, the temperature generated by the wear of the oil seal accelerates the deterioration of the oil and produces impurities and moisture, which further contributes to the decline in the performance of the oil seal（mechanical seal） in the oil chamber, causing the stator winding in the motor chamber to become damp and the insulation resistance to decrease.

III .Structure and function of mechanical seal
The mechanical seal consists of a stationary seat & a rotary face, a compensation ring, a snap ring, and an auxiliary seal. The stationary seat is made of alloy material, and the working end face is precision machined. The outer wall and end face are surrounded by an L-shaped rubber bushing, which is installed in the stationary seat seat at the motor shaft extension end. The rotary face of the mechanical seal is made of graphite or alloy material, and the auxiliary axial seal installed on the inner ring of the rotary face is an O-type fluororubber ring. The compensation ring is made of stainless steel and has multiple springs evenly distributed around the circumference to elastically compensate the axial displacement of the rotary face. There is a set screw in the circumference of the compensation ring, which plays an axial positioning and anti-rotation role when adjusting the mechanical seal. The snap ring plays an axial positioning and reinforcement role in the compensation ring.

The two are made of tungsten carbide (stationary seat) and tungsten carbide (rotary face) materials, and are made of tungsten carbide (stationary seat) and graphite ( rotary face) material matching.