B sealed cover with the pump seal; the c sleeve and the shaft seal; seal d snap ring and sleeve; e dynamic, static ring seal between the seal between the stationary ring and stationary ring seat;
Leakage test operation. Pump mechanical seal after a static test, the high speed operation is generated by rotation of the centrifugal force, will inhibit the leakage of the medium. Therefore, commissioning mechanical seal leakage exclude shaft and end cap seal failure, basically due to dynamic friction pair of stationary ring caused by the destruction. The main factors causing friction pair of seal failure:
a stationary ring seal loose when the snap ring axial float, stationary ring from the stationary ring seat; the b ring seals tight, spring can not adjust the amount of axial float ring the amount of compression on the installation of mechanical seals; c too large, leading to friction pair the end face serious wear, abrasions; the d design selection, the seal faces pressure is low or the sealing material Lengsuo greater so on. The above-mentioned phenomena often appear in the commissioning, by appropriate adjustment of the static ring seat can sometimes be eliminated, but most need to be re-disassembly, replace the seal; e medium granular substance, running into the friction pair testing dynamic stationary ring seal faces; f operation, due to the time of cavitation pressureout abnormal phenomenon, caused by the large axial force, so that moving, stationary ring contact surface separation;
Install static test leak
(2) caused due to the loss of lubricating film and the end face of the two sealing failure:
a) the presence of load due to face seal, start the pump in the sealed chamber when the lack of liquid and dry friction occurs; b) medium below the saturation vapor pressure, so that the end face of the liquid film to flash, the loss of lubrication; c) as a medium volatile the saturated vapor pressure of products, in the mechanical seal cooling system to fouling or blocking, since the medium to generate heat so Friction stir the liquid and the rotating element to rise, and also cause the pressure of the medium is lower than the saturated vapor pressure condition.
3. Mechanical seal failure due to corrosion caused by:
a) sealing surface pitting, even penetrate. b) easy to produce tungsten carbide ring with stainless steel seat, such as welding, use stainless steel seat intergranular corrosion; c) welded metal bellows, spring stress together with medium corrosion prone to rupture.
4 due to the wear of the seal faces causing the seal failure:
a) For a medium containing solid particles, the sealing surface into the solid particles are the main reasons leading to seal failure. The solid particles from entering from the end face of the friction pair abrasive seals dramatic wear and failure. Reasonable gap sealing surface and the balance of the mechanical seal, seal face liquid film flash are caused to open the main reason for leaving the solid particles into the end face. b) the degree of balance of the mechanical seal β also affects seal wear. Under normal circumstances, the degree of balance β = about 75%, most suitable. β <75%, the amount of wear, although reduced, but the leak increases, opens the possibility of the sealing surface increases. Mechanical seal for high load (high PV values), since the end face of the frictional heat, β and generally 65% ??to 70% is appropriate, the low-boiling hydrocarbon medium, the temperature is more sensitive to the medium gasification, to reduce the The influence of the heat of friction, β taken at 80% to 85% as well. c) poor abrasion resistance of the materials used by the friction pair, a large coefficient of friction, the face pressure (including the spring pressure) is too large, will shorten the life of the mechanical seal. Commonly used materials, wear resistance arranged in order of: silicon carbide - carbon graphite, carbide - carbon graphite, ceramics - carbon graphite, sprayed ceramic - carbon graphite, silicon nitride ceramic - carbon graphite, high-speed steel - carbon graphite, surfacing carbide - carbon graphite.
5. Effect due to the high temperatures and mechanical seal failure:
a) thermal cracking is a high-temperature oil pump, diesel pump, pump back to the refinery, atmospheric and vacuum bottoms pump is the most common failure phenomenon. Sealing surface due to dry friction, cooling water suddenly interrupted, impurities into the sealing surface, evacuation, etc., will cause the torus radial cracks; b) graphite charring is one of the main reasons of the use of carbon - graphite ring seal failure . In use, the graphite ring once more than the allowable temperature (typically of from -105 ~~ 250 ° C), the surface will be precipitated resin the vicinity of the friction surface resin carbonization, foaming softening binder, sealing surface leakage, seal failure; c) auxiliary seals (eg, fluorine rubber, ethylene-propylene rubber, rubber) in excess of the allowable temperature will rapidly aging, cracking and hardening miss bombs. Now use flexible graphite, high temperature resistance, corrosion resistance and good, but its resilience. And easy to rattle easily damaged installation.
6. Installation, operation or device itself generates error caused by mechanical seal leakage:
a) equipment in operation, mechanical seal leak reasons mainly: 1) dynamic and static ring and sleeve form scale spring miss bombs can not compensate for the wear of the sealing surface; 2) the inappropriate choice of ring material, swelling miss bombs ; 3) damage or deformation of friction pair and not be able to run together cause steering does not leak 4) spring; 5) too much vibration equipment operation;; 6) seal ring cracking occurs. 7 pump impeller axial runout exceeds the standard shaft occurrence of of cyclical vibration and unstable process operation, seal cavity pressure often changes are periodic leaks cause the seal;
b) due to poor installation, causing mechanical seal leakage. Mainly in the following aspects: 1) dynamic and static ring seals the wrong size, damaged, or has not been pressed; 2) dynamic and static ring surface of a foreign body; 3) sleeve seals corrosion at point 4) moving direction of the stationary ring, V-ring fitted anti or install anti-side; 5) the end face of the seal chamber is the axis perpendicular to the degree is not enough; 6) bushings at the leak, seals are not installed or pressing force is not enough; 7) moving stationary ring contact surface uneven bumps installation damage; 8) the spring force is not uniform, single spring is not vertical, multi-springs of varying lengths;
c) shaft interference is too large
d) pumps stop for some time and then start to leak, this is mainly because the vicinity of the friction pair medium solidification, crystallization, scale on the friction pair, spring corrosion obstruction miss bombs.
 



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