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Mechanical seal installation, operation, maintenance and failure analysis

by:Lepu Seal     2022-01-21

Mechanical seals have been widely used in petrochemical and other industrial sectors due to their advantages of good sealing and long service life. However, if the mechanical seals are improperly installed and operated and maintained, accidents will often occur. Seals are not as popular as packing seals. Because mechanical seals are relatively precise components, correct installation procedures, strict operating specifications, and reasonable maintenance systems are powerful measures to ensure the performance and normal operation of mechanical seals. Mechanical seal installation 1. Preparations and precautions before installation 1. Take out the mechanical seal to be installed from the packing box and place it on a clean surface, protect the sealing surface, and arrange all labels and documents for inspection; 2. Check the mechanical seal 3. Check the surface quality of each part, especially the seal of the dynamic and static rings. Whether the end face is bumped or scratched, if it is damaged, it must be repaired or replaced. 4. Check the axial string volume, radial runout, related verticality, concentricity, and surface roughness of the host with the mechanical seal installed according to the technical requirements. , matching size and coupling requirements for the pump, etc. 1. Axial series volume: the requirement is not more than 0.1mm, generally between 0.025~0.1mm, the axial series volume is too large, which makes the mechanical seal spring specific pressure unstable , causing excessive wear or leakage of the end face of the seal, and damage to the seal due to the shaking of the shaft, which is more obvious in the graphite ring. Local corrosion, erosion or wear at the contact of 0.1mm, can reduce the harm caused by too large axial series, on the other hand, if the axial series is too small, such as less than 0.025mm, it will have adverse effects on the bearing.
1. Preparations before startup
1. Comprehensively check whether mechanical seals and auxiliary devices, as well as pipelines, valves, instruments, etc. are fully installed. The pipeline must be cleaned to prevent clogging, which is especially important for new devices. Because impurities often enter the seal from the pipeline and affect the seal For performance, the entire system is to be evacuated to prevent the formation of air locks high in the seal chamber, resulting in dry friction operation.
2. Before starting, a static pressure test should be carried out, and the test pressure is the same as the working pressure; check the mechanical seal itself and related sealing points and joints for leakage, if there is leakage, try to deal with it.
3. Press the rotary steering wheel of the pump, and it can be delivered to use after meeting the requirements.

Second, start the operation
1. Before the main engine is started, the sealed cavity should be kept filled with liquid or sealed medium. If there is a separate auxiliary sealing system, it should be started first, and the cooling water system should also start to flow (the last stop when it is stopped); For medium or medium with high viscosity, use steam to heat the sealed cavity to melt the medium. Before starting, it must be cranked to prevent the soft ring from breaking due to sudden start.
2. Before normal use, perform constant cutting operation to observe whether the temperature rise of the sealing part is normal. If there is light leakage, it can be run for a period of time to make the end face fit more evenly, until the leakage is gradually reduced to normal. .If the leakage still does not decrease after 1~3 hours of operation, it needs to be stopped for inspection.
3. Boosting and heating operation: The mechanical seal that has passed the test of normal pressure operation should do boosting and heating operation in time with the same operating conditions. Boosting and heating can be carried out separately. The process of boosting should be slow, pay attention to boosting Changes that may occur in the process of (or heating), such as whether the parts collide, whether the end faces are disengaged, whether the frictional heating is too fast, whether the anti-rotation pin is disengaged or damaged, whether the pressure is stable (the pressure fluctuation is required to be no more than ±0.1 MPa) and whether there is leakage at the sealing ring and sealing end face, etc. If everything is normal, it can be put into production.
Causes of mechanical seal failure and treatment measures
1. Causes of mechanical seal failure The main reasons for mechanical seal failure are as follows: 1. Failure caused by poor mechanical seal itself;
2. Failure caused by host problems;
3. Failures caused by improper selection and application of mechanical seals;
4. Failures caused by improper installation and operation and poor management;
5. Failures caused by poor auxiliary devices or insufficient understanding of auxiliary devices. The failure phenomena of mechanical seals include: end face wear, thermal cracking of sealing rings, deformation, corrosion, loss of elasticity or breakage of elastics, damage to auxiliary sealing rings, etc.
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