In general, the overhang of the shaft sleeve, the seal between the cover and the pump leaks easier to detect and resolve, subject to careful observation, especially when the work of medium or high pressure liquefied gases, toxic gases, the relative difficulty more. The rest of the leak is difficult to intuitively judge in Discrimination and shall be long-term management and maintenance practice, based on observed symptoms of the leak, analysis and research to draw the right conclusion.
1, leakage analysis and determine
1. Static leak test when installed. Mechanical seal installation is completed, generally try to be quiet, observe the leakage. If leakage was smaller, and more for the ring or the stationary ring seal problems; leakage is large, it indicates that the dynamic and static ring friction pair between a problem. Leakage in the initial observation to determine leak location based on the observation car and then manually set, if no significant changes in leakage is static and dynamic sealing ring problem; if Barring a significant change in the leakage rate can be determined is fixed, Static Friction ring problems; medium along the axial leak jet, the ring seal problems are mostly medium to leak around the injection or leakage from the water cooling holes, the multi-ring seals for the static failure. In addition, the leakage channel can exist, but in general there are differences between primary and secondary, as long as careful observation, familiar with the structure, must be able to judge correctly.
2. Commissioning when the leak. After pump mechanical seal static tests, running high-speed rotation of the centrifugal force, will inhibit the media leak. Therefore, when the mechanical seal leakage in the commissioning rule out axis and cover seal failure, the essentially as static and dynamic friction pair rings caused by the destruction. Vice seal failure caused friction factors are:
(L) operation, for taking the time, cavitation, pressure-and other anomalies, caused by large axial force, so that dynamic and static ring contact surface separation;
(2) When the installation of mechanical seal excessive compression, resulting in severe wear of friction pairs face, abrasions;
(3) The tight ring seals, spring can adjust the ring volume of the axial fluctuation;
(4) stationary ring seal is too loose, when the ring axial float, the static rings from the stationary ring seat;
(5) working media are granular materials, in operation into the pair, testing of dynamic and static ring seal faces;
(6) design selection is wrong, or the seal faces lower than the pressure of sealing materials expand and contract more so. The phenomenon that often appear in the test run, sometimes through
Been adjusted to eliminate static and other Central Block, but the majority need to dismantle, replace the seal.
3. Normal operation of a sudden leak. Centrifugal sudden leak in the operation of a small number is due to normal wear and tear or has reached the life of the majority is due to a greater or operating conditions change, caused by improper maintenance.
(1) for taking the time, gas pressure-loss or a longer time, resulting in seal damage;
(2) The actual output of the pump is low, a large number of medium circulation pump, heat build up, causing media gasification, resulting in seal failure;
(3) Back flow is too large, causing suction tube side of the bottom of the container to rise again, damage to seal;
(4) longer outage, reboot without manual plate car, Friction due to adhesion and to rupture the sealing surface;
(5) medium corrosion, polymerization, increased Gellan gum substances;
(6) rapid changes in temperature;
(7) conditions frequently change or adjustment;
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Mechanical seal leakage caused by corrosion
(!) Surface corrosion
As the corrosive medium erosion, mechanical seals and surface corrosion occurs, severe corrosion can occur when perforated, spring is more obvious pieces, stainless steel, reduce surface erosion.
(2) pitting corrosion
Spring cover a large area often appear or regional point of pitting corrosion, and some lead to perforation, the use of such localized corrosion on the seal is still not lead to very serious consequences, but should also be replaced during overhaul.
(3) intergranular corrosion
Stainless steel ring tungsten carbide ring seat to brazing connection, the use of stainless steel Block prone to corrosion, to overcome the sensitizing effect of stainless steel should be solution heat treatment.
(4) stress corrosion cracking
Welded metal bellows, springs and other media in the stress corrosion of working together, often rupture, due to the sudden spring break Ershi seal failure, generally increase the spring wire diameter to be addressed.
(5) crevice corrosion
Ring the hole and between the sleeve surface, between the screw and screw, O-ring and the sleeve between the gap as the difference between internal and external media concentration caused crevice corrosion, in addition to ceramic ring and metal ring Zama also Crevice corrosion occurs, generally coating the surface of ceramic bushings, with ring binder in surface coating to reduce the gap to corrosion.
(6) electrochemical corrosion
Dissimilar metals in the medium often lead to electrochemical corrosion, it makes with ring loose, affecting sealing, then the general has taken office in the Xiang adhesive coating method to be overcome.
5. Heat loss effect
(1) thermal cracking
Such as the sealing surface is dry friction, cooling suddenly interrupted, impurities into the sealing surface, taking the time and so on, will lead to ring radial cracks appeared on the surface, so that rapid wear of the dual ring, sealing surface leakage increased rapidly. WC was common for thermal cracking.
(2) foaming, carbonization
If the use of graphite ring more than the allowable temperature, its surface precipitation resin, resin will occur near the friction surface carbonization, when binder, the foam will soften, so that sealing surface leakage increases, seal failure.
(3) aging, cracking, swelling
Rubber over allowable temperature to continue to use, will rapidly aging, cracking, loss of shells harden. Swelling and loss of organic medium is so elastic, these all contribute to seal failure.
That where heat loss caused by seal failure, the key is to minimize friction and heat, to improve cooling, sealing plane of the drastic changes in temperature does not occur.
6. Wear failure
Friction wear resistance if the timber is poor, the friction coefficient larger than the pressure face (including the spring pressure) is too large, the sealing surface into sealing surface of solid particles, which made the excessive wear caused by seal failure. Balanced mechanical seal used to reduce the face than the reduction of pressure and install the appropriate spring pressure, enabling to overcome the wear and tear caused by the failure, in addition, a good selection can reduce the wear of friction pair materials. Wear-resistant material according to the order of arrangement for the tungsten carbide - carbon graphite, carbide - carbon graphite, ceramic (aluminum oxide) - carbon graphite, paint ceramic - carbon graphite, silicon oxide ceramic - carbon graphite, high speed steel - carbon graphite, surfacing carbide - carbon graphite.
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Installation, operation and other failures of
(1) or a static water leak test
As bad installation, mechanical seal or a static pressure test water will leak. Installed with the following aspects of non-performing.
a. dynamic and static ring contact surface uneven, install a bruised, damaged.
b. dynamic and static ring ring size is incorrect, damaged or not compressed.
c. dynamic and static folder foreign body into the ring surface.
d. static and dynamic loading ring against the direction of V-ring, or when the anti-side installation.
e. set screws are not tightened, the spring seat back.
f. sleeve leak and seal compression is not installed or not.
g. If the direction hand shaft leakage, there are reasons: uneven spring force, a single spring is not vertical, more than the number of springs of different lengths or less; sealed chamber with the axis perpendicular to the face is not enough.
h. static ring compression uneven.
(2) from the installation, operation and other leaks caused by cyclical
If the pump impeller in operation axial movement of more than standard shaft vibration periodically and process operation instability, frequent changes in seal cavity pressure will result in seal leakage periodically.
(3) recurrent leak
a. ring, stationary ring contact with regular roof deformation will cause leakage. Such as the face than the pressure of excessive friction heat caused by dynamic and static part of the thermal deformation; sealing part structure is irrational, the intensity is not enough distortion; as material processing causes residual deformation produced; installation Shouli Bu equal parts, are Seals deformation of the main reasons.
b. Xiang installation or bonding of the dynamic and static leakage caused by the pump ring joints recurrent leakage, due to the improper charging process Xiang residual deformation, improper use of materials, the amount of interference sub-requirements, bonding agents will lead to joint deterioration leakage.
c. Friction can run together without damage or deformation caused by leakage.
d. Friction folder into the particle impurities.
e. spring pressure is too small.
f. ring selection is not correct, swelling failure.
g V-ring fitted against.
h. dynamic and static seal ring axis is not perpendicular to the face of error is too large.
i. Compression ring, the drive pin, anti-resale withstand parts.
j. not big spring rotation.
k. shaft vibration.
l. dynamic and static ring and the sleeve after the formation of scale could not wear compensation displacement.
m. Office installation ring groove or sleeve parts have corrosion pits.
n. face than the pressure is too large, ring surface cracks.
o. poor floating static ring.
p. assist device in question.
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Sudden leak
For the following reasons, pump seal leakage occurs suddenly.
(1) pump strong vibration, taking the time to destroy the friction pair.
(2) spring break.
(3) anti-resale off or drive off broken and useless.
(4) assist devices are failures of the static and dynamic sealing surface ring due to Sudden cold deformation or cracks.
(5) As the temperature changes, friction pair condensation occurs around the medium, Crystallization seal.
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Period of time the pump stops when the leakage expenditure
Friction in the vicinity of the solidification media, crystallization, Pair with scale; spring of corrosion, clogging and loss of elasticity, can cause the pump to re-start when the leak.
