1. leakage in static test
After the mechanical seal is installed and debugged well, the static test should be carried out, and the leakage is observed. If the leakage is small, there are many problems in the ring or static ring seal ring, and when the leakage is large, there is a problem in the friction pair between the dynamic and static rings. In the preliminary observation of leakage, the leakage judgment based on the part of, and then manually turning observation, if leakage without significant changes in the static and dynamic seal ring problems; such as the disk when there are significant changes in leakage can be concluded that the dynamic, static friction ring problems; such as leakage along the axial direction is injection. Dynamic ring seal ring problems are medium to leak around the jet or water leaked from the cooling hole, mostly static seal ring failure. In addition, the leakage channel can also exist at the same time, but generally there are primary and secondary differences, so long as it is careful and familiar with the structure, it will be able to judge correctly.
2. leakage in trial operation
After the mechanical seal of the pump is tested, the centrifugal force produced by high speed rotation will inhibit the leakage of the medium. Therefore, the leakage of mechanical seal in the trial operation is mainly caused by the failure of the friction pair of the movable and static ring after the seal failure of the exclusion shaft and the end cover. The main factors that cause the failure of the friction pair seal are as follows:
(1) in the operation, due to the abnormal phenomena such as pumping, cavitation and pressure, the larger axial force is caused, and the contact surface of the dynamic and static ring is separated.
(2) the compression amount of the mechanical seal is too large, which leads to the serious wear and abrasion of the end face of the friction pair.
(3) the seal ring of the movable ring is too tight, and the spring can not adjust the axial floating amount of the movable ring.
(4) the static ring sealing ring is too loose, and the static ring is separated from the static ring when the moving ring is floating in the axial direction.
(5) there are granular material in the working medium, running in the friction pair, and detecting the seal end face of the dynamic and static ring.
(6) the design type is mistaken, the seal face's specific pressure is low or the sealing material is cold shrink and so on. The above phenomena often appear in the trial operation, and sometimes it can be eliminated by proper adjustment of the static ring seat, but most of them need to be reassembled and replaced.
3. failure caused by the loss of the lubricating film on the two seal face
A) due to the existence of end face seal load, dry friction occurs when the pump is lack of liquid when the sealing cavity is lack of liquid.
B) the pressure of the medium is lower than the saturated steam pressure, which makes the surface film flash and lose the lubrication.
C), if the medium is a volatile product, when the mechanical seal cooling system is fouling or blocking, the saturated vapor pressure of the medium will rise due to the friction of the end face and the heat produced by the stirring element of the rotating element, which will also cause the medium pressure to be lower than its saturated vapor pressure.
4. failure of mechanical seal caused by corrosion
A) seal face point erosion and even penetrate.
B) due to the welding of tungsten carbide ring and stainless steel seat, intergranular corrosion is easy to be produced in the stainless steel base in use.
C) welded metal bellows and springs are easily broken under the joint action of stress and medium corrosion.
5. mechanical seal failure due to high temperature effect
A) high-temperature heat pump is split, such as diesel pumps, to pump oil refining, atmospheric and vacuum tower bottom pump failure is the most common phenomenon. When the dry friction, the cooling water suddenly break down at the sealing surface, and the impurities enter the sealing surface and the air, the radial cracks in the torus will appear.
B) graphite carbonization is one of the main causes of sealing failure when carbon - graphite rings are used. Because during the use, if the graphite ring once exceeds the allowable temperature (usually -105 ~ 250 degrees), the resin will be precipitated on the surface. The resin will be carbonized near the friction surface. When there is a binder, it will soften and soften, and increase the leakage of the sealing surface and seal failure.
C) auxiliary seals (such as fluoro rubber, ethylene propylene rubber, all rubber) will be rapidly aging, cracking and hardened at a temperature exceeding the allowable temperature. The flexible graphite used now has good resistance to high temperature and corrosion resistance, but its resilience is poor. And easy to crack, easy to damage when the installation.
6. seal failure due to wear of seal face
A) the wear resistance of the material used by the friction pair, the large friction coefficient and the overpressure of the end surface (including the specific pressure of the spring) will shorten the life of the mechanical seal. For the commonly used materials, the order of wear resistance is: silicon carbide carbon graphite, carbide alloy carbon graphite, ceramic carbon graphite, spray ceramic, carbon graphite, silicon nitride ceramic carbon graphite, high-speed steel carbon graphite, hardfacing carbide graphite carbon graphite.
B) for a solid particle medium, the main cause of sealing failure is the entry of the seal surface into the solid particles. Solid particles enter the end of the friction pair to play the role of abrasive agents, causing severe wear and failure of the seal. The main reason for the entry of solid particles is the reasonable clearance of the sealing surface, the degree of balance between the mechanical seal and the flashing of the liquid film on the sealing face.
C) the balance of the mechanical seal is β it also affects the wear of the seal. In general, the balance of &beta and =75% are most suitable. β <75%, although the wear amount is reduced, the leakage increases, and the possibility of opening the seal face increases. For mechanical seals with high load (high PV value), because of the larger frictional heat of the end faces, &beta is generally suitable for 65% ~ 70%. For low boiling hydrocarbon medium, because of the sensitive temperature to the gasification of medium, &beta is the most effective way to reduce the friction heat, and 80% ~ 85% is good.
7. leakage of mechanical seal caused by the errors produced by the installation, operation, or equipment itself
A) due to poor installation,
- Close This Page
- Recommendation：
- Browse：
