Pump mechanical seal a wide range of different models, but there are five main points of leakage: (l) the seal between the shaft sleeve and the shaft; (2) the seal between the moving ring and the shaft sleeve; (3) ; (4) the seal between the stationary ring and the ring seat; (5) the seal between the seal cap and the pump body. 1. Static test installation leaks Mechanical seal installation and commissioning, the general should be static test, observe the amount of leakage. If the leakage is small, mostly ring or static ring seal problems; leakage is large, then that dynamic and static friction ring there is a problem. In the initial observation of the leakage, to determine the leakage site, based on manual observation disk, if the leakage was no significant changes in the static and dynamic ring seal problems; such as the disk when there is a significant change in leakage can be concluded that the move, Static friction ring there is a problem; such as the leakage of media along the axial injection, the dynamic ring seal there are many problems, leakage to the surrounding medium jet or water leakage from the hole, the more static ring failure. In addition, the leak channel can exist at the same time, but generally there are major and minor differences, as long as careful observation, familiar with the structure, we must be able to correctly judge. 2. Leakage during commissioning. Pump mechanical seal after static test, the centrifugal force generated by high-speed rotation of the operation, will inhibit the media leakage. Therefore, the test run when the mechanical seal leakage excludes the seal between the shaft and the end cover, basically due to dynamic and static friction ring caused by damage. The main factors that cause the failure of the friction seal are: (1) the operation, due to time, cavitation, pressure and other anomalies, causing a large axial force, the dynamic and static contact surface separation; (2) Mechanical seal when the amount of compression is too large, leading to serious friction end face wear, abrasions; (3) ring seal is too tight, the spring can not adjust the axial displacement of the moving ring; (4) (5) There is granular material in the working medium, into the friction pair in operation, flaw detection dynamic and static ring seal face; (6) design selection is wrong, the seal Low end pressure or sealing materials such as larger shrinkage. These phenomena often appear in the trial operation, and sometimes can be eliminated by adjusting the static ring seat, etc., but most need to re-disassemble, replace the seal. Due to the failure of the two sealing end faces to lose the lubricating film: a) dry friction occurs when the seal chamber is lack of liquid due to the end seal load; b) the sub-saturated vapor pressure of the medium causes the end liquid film to flash Steaming, loss of lubrication; c) If the medium is a volatile product, when the mechanical seal cooling system fouling or obstruction, as a result of friction and rotation of the rotating element liquid heat stirring medium saturation vapor pressure increases, but also caused the media pressure Below its saturated vapor pressure conditions. Mechanical seal failure due to corrosion: a) The sealing surface pitting and even penetrating. b) As the tungsten carbide ring and stainless steel seat and other welding, easy to use in the production of stainless steel seat intergranular corrosion; c) welding metal bellows, springs and other stress and corrosion under the joint action of the common rupture. Mechanical seal failure due to high temperature effects: a) Hot cracking is the most common failure of high temperature oil pumps such as oil residue pumps, refueling pumps, and atmospheric and vacuum pump towers. In the case of dry friction, sudden interruption of cooling water, entry of contaminants into the sealing surface and evacuation of the sealing surface, radial cracks will occur in the torus; b) Graphite carbonization is one of the major causes of seal failure when using carbon-graphite rings . In use, if the graphite ring once exceeded the permissible temperature (usually -105 ~ 250 ℃), the surface of the resin will precipitate, friction near the surface of the resin will occur carbonization, when there is a binder, it will foam softening, So that the sealing surface leakage increases, the seal failure; c) auxiliary seals (such as fluorine rubber, ethylene propylene rubber, all rubber) will exceed the allowable temperature, it will quickly aging, cracking, hardening of the shells. Flexible graphite now used high temperature, corrosion resistance is better, but its poor resilience. And easy to brittle, easy to damage when installed. Seal failures due to wear of seal faces: a) Materials used for friction pairs have poor wear resistance, large coefficient of friction, and excessive end pressure (including spring pressure), which shortens the service life of the mechanical seal. Commonly used materials, according to the order of wear resistance: silicon carbide - carbon graphite, cemented carbide - carbon graphite, ceramic - carbon graphite, painted ceramic - carbon graphite, silicon nitride ceramic - carbon graphite, high-speed steel - Carbon graphite, hardfacing surfacing - Carbon graphite. b) For media containing solid particles, the entry of the sealing surface into the solid particles is the main cause of failure of the seal. Solid particles into the friction side from the role of abrasive agent, so that severe seal wear and failure. Reasonable sealing surface clearance, as well as the degree of mechanical seal balance, as well as the sealing surface of the liquid film flash are the main open end to open the solid particles into the main reason. c) The degree of mechanical seal balance β also affects seal wear. Under normal circumstances, the balance of β = about 75% of the most appropriate. β Mechanical seal leakage due to errors in installation, operation, or the equipment itself: a) Leakage of the mechanical seal due to poor mounting. Mainly in the following areas: 1) dynamic and static contact ring surface uneven, bruised during installation, damage; 2) dynamic and static ring seal size is wrong, damaged or not compressed; 3) dynamic and static ring surface There is a foreign body; 4) moving, static ring V-ring mounted in the opposite direction, or install the anti-edge; 5) leakage at the sleeve, the ring is not installed or pressing force is not enough; Vertical, multi-spring length varies; 7) sealed chamber end face and the shaft perpendicularity is not enough; 8) sleeve on the seal ring corrosion points. b) The equipment is in operation, the mechanical seal leaks are mainly due to: 1) axial displacement of the pump impeller exceeds the standard, the shaft vibration occurs periodically and the process is not stable, the pressure inside the sealed chamber and other changes often lead to sealed cycle Sexual leakage; 2) the friction pair damage or deformation can not run together to cause leakage; 3) improper selection of sealing material, swelling bullet; 4) large spring steering is not right; 5) equipment operation vibration is too large; Scale formation between the ring and the shaft so that the spring can not compensate for the loss of the seal surface wear and tear; 7) seal ring cracking and so on. c) The pump leaks after restarting for a period of time. This is mainly due to solidification of the medium near the friction pair, scaling of the friction pair, corrosion of the spring, and blockage of the missile. d) pump shaft interference is too large.
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