Countermeasure: Adopt double-end face mechanical seal, which helps improve lubrication conditions and enhance sealing performance.
Countermeasure: For corrosive media, rubber parts should be made of high-temperature resistant, weak-acid and weak-base resistant fluororubber.
Countermeasure: When assembling the mechanical seal, the spring compression must be carried out according to regulations, without excessive or insufficient phenomena. Under high-pressure conditions, measures should be adopted for mechanical seals. To ensure reasonable force on the end faces and minimize deformation, materials with high pressure strength such as hard alloy and ceramics can be used, and cooling and lubrication methods should be enhanced. Reliable transmission methods, such as keys and pins, should also be selected to prevent leakage in home installations.
① Ensure the cleanliness of the lower end cover and oil chamber. Lubricating oils that are not clean should be prohibited from assembly.
Due to other issues causing mechanical seal leakage:
(1) Mechanical seal leakage caused by high pressure and pressure waves: Due to excessive spring contact pressure and total pressure design, and when the sealing cavity pressure exceeds 3MPa, it will result in excessive end face contact pressure, making it difficult to form a liquid film. This leads to severe wear, increased heat generation, and thermal deformation of the sealing surface.
(2) Insufficient lubrication at the sealing surface causing dry friction or damaging the sealing end face.
(1) After disassembling most submersible pump mechanical seals, it is found that the auxiliary sealing parts of the stationary and rotating rings have lost elasticity; some have even corroded, leading to massive leaks or shaft wear. High temperature, weak acids, and weak bases in sewage corrode the auxiliary rubber seals of the stationary and rotating rings, causing excessive mechanical leakage. The material of the stationary and rotating ring rubber seals is Nitrile-40, which cannot withstand high temperatures or acids and alkalis. When the sewage is acidic or alkaline, corrosion easily occurs.
Countermeasure: The height of the lubricating oil level in the oil chamber should be added above the sealing surfaces of the rotating and stationary rings.
② The main component causing shaft wear is the rubber bellows, which is due to poor lubrication at the upper end sealing surface. The friction torque between the rotating and stationary rings is greater than the transmitted torque between the rubber bellows and the shaft, resulting in relative movement.
(2) Mechanical seal leakage caused by vacuum operation: During start-up and shutdown, due to blockages in the pump inlet or gas in the pumped medium, negative pressure may occur in the sealing cavity. If the sealing cavity is under negative pressure, it will cause dry friction at the sealing end face. Internal mechanical seals may experience air (water) leakage. The difference between vacuum sealing and positive pressure sealing lies in the directionality of the sealed object, and mechanical seals also have adaptability in a certain direction.
① BIA type double-end face mechanical seal, reverse pressure state is an unfavorable working condition. Particles and impurities in the medium can easily enter the sealing surface, causing seal failure.
(1) Small pumps below 715kW often experience shaft wear. The main positions of shaft wear include: the auxiliary seal circle of the rotating ring, the position of the stationary ring, and a few springs showing signs of shaft wear.
(1) Large axial movement of the pump rotor and large interference fit of the auxiliary seal with the shaft prevent the rotating ring from moving flexibly on the shaft. After the pump reverses, and the rotating and stationary rings wear, no compensation displacement can be obtained.
Due to medium-induced leakage:
(3) To solve the above problems, the following measures are now taken: Leakage caused by pressure:
③ The auxiliary seals of the rotating and stationary rings lose elasticity due to corrosion by weak acids and weak bases in sewage. Some have already corroded and lost their function, causing shaft wear.
③ Select different types of mechanical seals based on different application media. For high-head pumps, the mechanical seal structure should be redesigned. For corrosive media, rubber should be selected as fluororubber resistant to weak acids and weak bases. Static rings should be equipped with anti-rotation pins.
(3) Periodic vibration of the rotor. The reasons include misalignment of the stator with the upper and lower end covers or imbalance of the impeller and main shaft, cavitation or bearing damage (wear). These situations will shorten the life of the seal and cause leakage.
There are still some unreasonable aspects in the design, selection, and installation of mechanical seals.
(2) The end face of the shaft (or sleeve) where the rotating ring seal is installed and the end face of the sealing gland (or housing) where the stationary ring seal is installed should be chamfered and polished to avoid damaging the rotating and stationary ring seals during assembly.
1. Periodic leakage
Mechanical seal leakage accounts for more than 50% of all repaired pumps. The good operation of mechanical seals directly affects the normal operation of water pumps. The following summarizes and analyzes this issue.
(1) The spring compression must be carried out according to specifications, without excessive or insufficient phenomena. The error should be ±2mm. Excessive compression increases the end face contact pressure, generating too much frictional heat, causing thermal deformation of the seal face and accelerating end face wear. Insufficient compression results in insufficient contact pressure between the rotating and stationary ring end faces, preventing sealing.
2. Shaft wear phenomenon caused by small submersible pump mechanical seal leakage
(2) Main causes of shaft wear:
Countermeasures: Corrections to the above problems can be made according to maintenance standards.
② The oil level in the mechanical seal oil chamber should be higher than the sealing surfaces of the rotating and stationary rings.
Mechanical seals are the primary cause of pump leakage. However, mechanical seals themselves are high-precision components with strict requirements. Design, mechanical processing, and assembly quality all have very high demands. When using mechanical seals, various factors affecting their use should be analyzed to ensure they meet the technical requirements of various pumps and usage media, while ensuring adequate lubrication conditions. Only then can long-term reliable operation of the seal be guaranteed.
The above summarizes the more common causes of mechanical seal leakage. Mechanical seals themselves are high-precision components with strict requirements. Design, mechanical processing, and assembly quality all have very high demands. When using mechanical seals, various factors affecting their use should be analyzed to ensure they meet the technical requirements of various pumps and usage media, while ensuring adequate lubrication conditions. Only then can long-term reliable operation of the seal be guaranteed.
Common leakage phenomena
Mechanical seals are also known as face seals. They have a pair of end faces perpendicular to the rotation axis. These end faces, under the action of fluid pressure and compensating mechanical external elastic forces, rely on the cooperation of auxiliary seals to maintain contact with another end and slide relatively, thereby preventing fluid leakage.
(2) Mechanical seal leakage caused by solid particle impurities: If solid particles enter the sealing end face, they will scratch or accelerate the wear of the sealing end face. The deposition rate of scale and oil on the shaft (sleeve) surface exceeds the wear rate of the friction pair, so that the rotating ring cannot compensate for the worn displacement. The service life of hard-to-hard friction pairs is longer than that of hard-to-graphite friction pairs because solid particles can embed into the sealing surface of graphite sealing rings.
Countermeasure: At positions where solid particles are likely to enter, mechanical seals with tungsten carbide-tungsten carbide friction pairs should be selected.