Principle of mechanical seal
Mechanical seal, also known as end seal, is a device used to solve the seal between the rotating shaft and the body. It is composed of at least a pair of fluid pressure perpendicular to the end face of the rotation axis and the elastic force (or magnetic force) of the compensation mechanism and the auxiliary seal to keep fit and slide relatively to form a device to prevent fluid leakage. Rotary fluid machinery such as compressors and reaction stirred tanks are also used for sealing gear boxes and ship stern shafts. Therefore, the mechanical seal is a universal shaft seal device.
There are two types of contact and non-contact. At present, most of them use contact mechanical seals. Non-contact mechanical seals are under development and have attracted people's attention. The mechanical seal is a non-functional component on the machine, but it plays a large role in reducing leakage and stabilizing production.
Working principle of mechanical seal
The role of mechanical seals
一、Improve machine efficiency and reduce energy consumption.
1. Reduce the internal leakage, external leakage and leakage of the machine and improve the volumetric efficiency of the machine. For example, Daqing Oil Refinery changed the impeller ring of coking 5FDJ5×2 centrifugal pump to a mechanical seal, which increased the pump efficiency by 3.6% and 5.6%.
2. Reduce friction loss and improve the mechanical efficiency of the machine. For example, changing the double-end face seal to a single-end face seal, the unbalanced type to the balanced type, and the closed end of the double-supported bottom-reduction pump (so-called beheading pump) can reduce friction loss and improve mechanical efficiency.
3. Change the sealing method to improve the efficiency of the machine or unit. For example, the canned pump is changed to a mechanically sealed pump to improve the efficiency of the motor; the magnetic drive pump is used to improve the efficiency of the machine.
4. Change the auxiliary system to reduce energy consumption and improve the efficiency of the unit. For example, the self-flushing of the hot oil pump was changed to the small-impeller cycle flushing; the double-end face seal was changed to the single-end face seal, saving the energy consumption of the oil sealing auxiliary system.
二、 save raw materials. For example, process fluid recovery, reduce or eliminate the loss of power steam and process fluid, reduce the loss of sealing oil, etc.
三、Improve machine reliability. For example, the leakage and life of the shaft seal determine the reliability of the shaft seal and the machine.
四、Safety and environmental protection. According to an investigation report from a Japanese factory, 32 of the 786 accidents were caused by leakage (42%). In addition, process fluid leakage will also cause environmental pollution, including atmospheric pollution, water pollution and workshop environmental pollution.
Essentials for installation and use of mechanical seals
1. The radial runout of the rotating shaft of the equipment should be ≤0.04 mm, and the axial runout should not be greater than 0.1 mm;
2. The sealing part of the equipment should be kept clean during installation, the sealing parts should be cleaned, the sealing end surface is intact, to prevent impurities and dust from being brought into the sealing part;
3. It is strictly forbidden to hit or knock during the installation process, so as to avoid damage to the mechanical seal friction pair and seal failure;
4. During the installation, the surface in contact with the seal should be coated with a layer of clean mechanical oil in order to be able to install smoothly;
5. When installing the static ring gland, the tightening screws must be evenly stressed to ensure the vertical requirements of the end surface of the static ring and the axis line;
6. After installation, push the moving ring by hand, which can make the moving ring move flexibly on the shaft and have certain elasticity;
7. After installation, turn the shaft with a hand wheel, the shaft should have no sense of weight;
8. The equipment must be filled with medium before operation to prevent the dry friction and the seal failure.
