Abstract: The causes of leakage of mechanical seals of general-purpose centrifugal pumps are analyzed, and various leak phenomena and parts that may cause leakage are explained. At the same time, some problems that may arise in the maintenance of common mechanical seals of centrifugal pumps are made A brief description.
1 Introduction to the structure principle
Mechanical seal is a rotary contact with the dynamic seal, which is in the fluid medium and the elastic element under the action of two perpendicular to the axis of the sealing surface close to the relative rotation, so as to achieve the sealing requirements.
Universal centrifugal pump mechanical seal a wide range of different models, but their leakage are basically reflected in the six: ① dynamic and static end of the ring; ② static and static ring box seal secondary seal; ③ moving ring and shaft Sets of auxiliary seal; ④ seal ring between the stationary box and seal body; ⑤ seal between the sleeve and the pump shaft; ⑥ moving ring inlaid with the structure of the Department.
The main structure shown in Figure 1.
Figure 1 mechanical seal structure diagram
1, bushings 2, gaskets 3, spring seat 4, spring 5, pushing ring 6, moving ring O-ring 7, retaining ring 8, moving ring 9, stationary ring O-ring 10, stationary ring 11, sealing filler 12 , Anti-pin 13, static ring seat 14, ring seat gasket 15, locking screws 16, pump shaft
2 mechanical seal fault performance
(1) seal the end of the fault: wear, thermal cracking, deformation, damage (especially non-metallic seal face).
(2) spring failure: relaxation, fracture and corrosion.
(3) Auxiliary seal failure: Assembling failure has broken pieces, rips, bumps, curling and twisting; non-assembled faults are deformed, hardened, ruptured and deteriorated.
Mechanical seal failure in the operation of the performance of vibration, heat, wear and tear, and eventually to the media in the form of external leakage.
3 mechanical seal leakage analysis and treatment
General mechanical seal pump after installation have to go through static and dynamic tests to confirm the mechanical seal installed correctly, when found to leak, to facilitate timely maintenance. In addition, during normal operation may also be a sudden leak, then you can conduct a comprehensive analysis based on the situation to confirm the cause of the mechanical seal leakage of the real reason, easy to solve. The following static pressure test leaks, periodic or paroxysmal and recurrent leakage of three cases were described.
3.1 static pressure test leak
a, sealed end face bumps, deformation, damage;
b, sandwiched between the sealed end of the sandwich granular impurities;
c, the seal end face due to loose or not tighten the screw, gland (static type static ring assembly for the pressure plate) is not pressed;
d, the accuracy of machinery and equipment is not enough to seal the end face is not fit;
e, static and dynamic ring sealing surface is not compressed or compressed enough or damaged;
f, static and dynamic ring "V" ring mounted reverse direction;
g, sleeve leakage, the sleeve seal assembly is not compressed or insufficient compression or damage.
Handling: Strengthen the assembly inspection, cleaning; in strict accordance with the technical requirements for assembly.
3.2 periodic or paroxysmal leakage
a, rotor assembly axial movement too much.
Treatment: Adjust the thrust bearing so that the shaft axial movement of not more than 0125mm.
b, the rotor components periodically vibrate.
Remedy: Find the cause and eliminate it.
c, the pressure in the sealed chamber often changes drastically.
Treatment: stable process operating conditions.
3.3 recurring leaks
3.3.1 Frequent leaks due to imperfections on the sealing face
a, spring compression (mechanical seal compression) is too small.
b, the amount of spring compression is too large, graphite ring cracked.
c, seal the width of the end face is too small.
Treatment: Increase the width of the seal face, and a corresponding increase in spring force.
a, compensation seal ring floating too bad (seal ring is too hard or hardening or compression is too large, compensation ring gap is too small).
Treatment: To compensate for the seal ring gap is too small, increasing the compensation ring gap.
b, diamond or bonded dynamic and static ring joint leakage (poor mounting process, there is residual deformation; uneven material; binder deformation).
c, moving, static ring damage or crack.
d, seal face wear, the ability to compensate disappears.
e, dynamic and static ring seal face deformation (end face by the spring force is too large, massage heat is too large, resulting in thermal deformation; seal parts structure is irrational, strength is not enough, force and deformation; due to processing and other reasons, the seal parts Residual deformation; uneven installation caused deformation).
Remedy: Replace defective or damaged seal ring.
f, moving, static ring Seal end face and shaft centerline deviation is too large, moving, static sealing ring relative parallelism difference is too large.
Remedy: Adjust the seal face.
3.3.2 Auxiliary ring caused by recurrent leakage
a, seal material is not right, wear, corrosion, temperature, anti-aging performance is too poor, resulting in premature deformation, hardening, rupture, melt and so on.
b, "O" ring seal the amount of compression is not, too large, easy to install bad, too small, the sealing effect is not good.
c, Install the ring shaft (or sleeve), seal the end cap and seal chamber, the surface of the "O" ring advancing burrs chamfer angle is not smooth or rounded enough.
Treatment: Burr and smooth chamfer, should be properly trimmed smooth, appropriate to increase the arc and chamfer, trim smooth.
d, "O" -shaped rings have broken, cracked, bruised, curled and twisted.
Handling: pay attention to the assembly matters.
3.3.3 Leakage due to spring defects
a, spring end deflection.
b, multi-spring type mechanical seal, the free height difference between the springs is too large.
3.3.4 Frequent leaks due to other parts
Such as transmission, tightness and thrust parts poor quality or loosening caused by leakage.
3.3.5 Recurrence due to rotor leakage
Such as rotor vibration caused by leakage.
3.3.6 Recurrent leaks due to mechanical seal aids
Flushing coolant flow is too large or too small, the pressure is too large or too small; pay attention to the wrong direction and position; pay attention to poor quality, impurities.
3.3.7 Frequent leaks due to media problems
a, medium suspended particles or crystallization of long-term accumulation of results, blocking the moving ring and the shaft, between the springs. Between the spring and the spring seat, so that compensation can not float ring seal, loss of compensation for the role of buffer.
b, suspended particles in the medium or crystal plugged between the sealing end face, so that the sealing end face rapid wear and tear.
Disposal: Before opening the car, flush the coolant valve for a period of time before turning on the car. For example, increase the flushing coolant; appropriately increase the medium inlet temperature; and increase the medium filtration and separation effect.
4 maintenance should pay attention to several issues
In the actual maintenance work, often prone to misunderstandings, mainly on the mechanical seal some of the subsidiary parts of the sealing principle of understanding of the deviation. The following questions on this area to make some simple instructions.
4.1 The larger the amount of compression spring seal better
In fact, the amount of compression spring is too large, will lead to rapid wear seal friction pair, the moment may burn. Excessive compression creates permanent plastic deformation of the spring, losing the ability to adjust the face of the moving ring, thus rendering the seal ineffective.
4.2 moving ring seal tighter and better
In fact, the ring is too tight moving ring harmless. One is to aggravate the wear and tear between the seal ring and the sleeve, causing premature leakage; two is to increase the axial adjustment of the moving ring, the resistance of the movement, frequent changes in the conditions can not be adjusted timely; Third, excessive fatigue fatigue damage; Fourth, the moving ring ring deformation, affecting the sealing effect.
4.3 static ring seal as tight as possible
Static ring seal is basically static, the relatively tight seal will be better, but too tight is also harmful. First, excessive deformation caused by the static ring, affecting the sealing effect; Second, static graphite material to the majority, generally more crisp, too easily lead to fragmentation caused by excessive force; Third, the installation and removal difficulties, easy to damage the static ring. The choice of the installation form of static ring should take full account of the floating ability under the corresponding conditions. After installation, it can automatically follow the moving torus and fit. If the static ring seal is too tight, the static ring can not float after installation Will have partial wear and tear, premature failure.
4.4 impeller lock nut as tight as possible
Mechanical seal leakage, the sleeve and shaft leakage (shaft leakage) is more common. Is generally believed that the leakage between the shaft impeller lock nut is not locked, in fact, there are many factors leading to shaft leakage, such as shaft washers failure, offset, impurities within the shaft, shaft and sleeve with a larger Department Shape and position error, the contact surface is destroyed, there is a gap between the various components on the shaft, the shaft thread is too long, etc., will lead to shaft leakage. Locking nuts over-locking can only cause premature failure of the shaft washer. In fact, tighten the lock nut moderate, you can always maintain a certain axis between the pad compression flexibility in the operation of the lock nut will automatically timely lock, the shaft is always in good seal.
4.5 new better than the old
Relatively speaking, the use of new mechanical seal better than the old, but if the new mechanical seal quality or material selection is not appropriate, or with large size error, it will affect the sealing effect. In polymeric and permeable media, the static ring does not change as well if it does not show excessive wear. Because the static ring in the static ring seat for a long time in a quiescent state, the polymer and impurities deposited as one, played a better seal. In fact, in many cases, the mechanical seal is no problem, as long as the appropriate adjustments and treatment, the mechanical seal can continue to use. In this way, both cost savings, but also reduce the workload, and can guarantee the sealing effect, is one thing many things.
4.6 disassemble the total is better than not dismantled
Once the mechanical seal leakage would be eager to overhaul, this approach is not entirely right, it should be based on the specific circumstances of the specific analysis. In fact, sometimes the mechanical seal is not damaged, just adjust the condition or adjust the seal to eliminate the leakage. This will not only avoid the waste of spare parts but also avoid the useless labor of maintenance personnel. In the overhaul, should be based on the actual situation to make the right judgments, so as to take targeted overhaul. According to the development trend of the seal, many seals are now designed into a cartridge design at the time of design, which effectively eliminates the above-mentioned many leaks.
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