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Generally speaking, it is easier to find and solve the leakage between the shafts where the shaft sleeves protrude, and the leakage between the sealing end cover and the pump body, but careful observation is required, especially when the working medium is liquefied gas or high-pressure, toxic and harmful gas, it is relatively difficult some. The rest of the leaks are difficult to distinguish and judge intuitively. Only by observing, analyzing and judging the symptoms of leakage on the basis of long-term management and maintenance practice can a correct conclusion be drawn.1. Leakage during installation static testAfter the mechanical seal is installed and debugged, it is generally necessary to conduct a static test to observe the leakage.If the leakage is small, it is mostly due to the problem of the moving ring or the static ring sealing ring. Manual cranking observation, if there is no obvious change in the leakage, there is a problem with the static and dynamic ring seals.When the leakage is large, it indicates that there is a problem between the dynamic and static ring friction pairs.In addition, leakage channels can also exist at the same time, but generally there is a difference between primary and secondary. As long as you observe carefully and are familiar with the structure, you can definitely make a correct judgment.2. Leakage during test runAfter the mechanical seal of the pump has passed the static test, the centrifugal force generated by the high-speed rotation during operation will inhibit the leakage of the medium. Therefore, the leakage of the mechanical seal during the test run is basically caused by the damage of the friction pair of the dynamic and static rings after the failure of the seals between the shafts and the end cover is excluded.The main factors causing friction pair seal failure are:(1) During operation, due to abnormal phenomena such as evacuation, cavitation, and pressure holding;(2) The compression amount is too large when installing the mechanical seal;(3) The moving ring sealing ring is too tight;(4) The static ring sealing ring is too loose;(5) There are granular substances in the working medium;(6) Failure caused by the loss of lubricating film on the two sealing end faces:a) Due to the existence of the load on the end face seal, dry friction occurs when the pump is started when the seal chamber lacks liquid;b) The pressure of the medium is lower than the saturated vapor pressure, so that the liquid film on the end surface flashes and loses lubrication;c) If the medium is a volatile product, when scaling or blockage occurs in the mechanical seal cooling system, the saturated vapor pressure of the medium will rise due to the friction of the end face and the heat generated by the stirring liquid of the rotating element, which will also cause the pressure of the medium to be lower than its saturated vapor pressure situation.(7) For a longer period of outage, there is no manual cranking when restarting;(8) The design selection is wrong.The above phenomenon often occurs during trial operation, and sometimes it can be eliminated by properly adjusting the static ring seat, etc., but most of them need to be disassembled and replaced to replace the seal.3. During the operation of the equipment, the main reasons for the leakage of the mechanical seal are:Centrifugal pumps suddenly leak during operation, a few are due to normal wear or have reached the end of their service life, and most are caused by large changes in working conditions or improper operation and maintenance.1) The axial displacement of the pump impeller exceeds the standard;2) Periodic vibration of the rotating shaft, unstable process operation, and frequent changes in the pressure in the sealing chamber will cause periodic leakage of the seal;3) Evacuation, cavitation or pressure holding for a long time, resulting in damage to the seal;4) The actual output of the pump is relatively small, and a large amount of medium circulates in the pump, and the heat accumulates, causing the medium to vaporize and resulting in seal failure;5) Corrosive, polymeric and gelling substances in the medium increase;6) Frequent changes or adjustments in working conditions;7) Scale is formed between the dynamic and static rings and the shaft sleeve, which makes the spring lose its elasticity and cannot compensate for the wear of the sealing surface;8) Sudden power failure or shutdown due to failure, etc.9) The equipment vibrates too much during operation;10) The friction pair is damaged or deformed and cannot run in, causing leakage;11) Improper selection of sealing ring material, swelling and loss of elasticity;12) The large spring turns incorrectly;13) Cracks in the sealing ring, etc.Centrifugal pump leaks suddenly during normal operation. If it cannot be found in time, it will often lead to major accidents or losses. It must be paid attention to and effective measures should be taken.4. The mechanical seal leaks due to poor installation. Mainly manifested in the following aspects:1) The size of the dynamic and static ring seals is wrong, damaged or not compressed;2) The direction of the dynamic and static V-shaped sealing rings is reversed, or the opposite side is installed;3) The contact surfaces of the dynamic and static rings are uneven, and they are bumped or damaged during installation;4) There are foreign objects on the surface of the dynamic and static rings;5) The verticality between the end face of the sealing chamber and the shaft is not enough;6) There are corrosion spots on the movable part of the sealing ring on the shaft sleeve.7) The spring force is uneven, the single spring is not vertical, and the multiple springs are of different lengths; 5. Mechanical seal failure caused by corrosion, high temperature, wear of sealing end face, etc.1) Mechanical seal failure due to corrosion:a) The sealing surface is corroded or even penetrated.b) Since the tungsten carbide ring is welded to the stainless steel seat, etc., the stainless steel seat is prone to intergranular corrosion during use;c) Welded metal bellows, springs, etc. are prone to rupture under the joint action of stress and medium corrosion.2) Mechanical seal failure due to high temperature effect:a) Thermal cracking is the most common failure phenomenon of high-temperature oil pumps, such as oil residue pumps, oil refining pumps, and atmospheric and vacuum tower bottom pumps. Due to dry friction at the sealing surface, sudden interruption of cooling water, impurities entering the sealing surface, evacuation, etc., radial cracks will appear on the ring surface;b) Graphite carbonization is one of the main causes of seal failure when using carbon-graphite ringsc) Auxiliary seals (such as fluorine rubber, ethylene propylene rubber, and full rubber) will rapidly age, crack, harden and lose their elasticity when the temperature exceeds the allowable temperature. The flexible graphite currently used has good high temperature resistance and corrosion resistance, but its resilience is poor, it is easy to be brittle at high temperature, and it is easy to be damaged during installation3) Seal failure due to wear of the sealing end facea) The materials used in the friction pair have poor wear resistance, high friction coefficient, and excessive end surface specific pressure (including spring specific pressure), etc., which will shorten the service life of the mechanical seal.b) For media containing solid particles, the entry of solid particles into the sealing surface is the main cause of seal failure. Solid particles enter the end face of the friction pair and act as abrasives, causing severe wear and tear of the seal to fail. The reasonable clearance of the sealing surface, the balance degree of the mechanical seal, and the flash evaporation of the liquid film on the sealing end surface are the main reasons for the opening of the end surface and the entry of solid particles.4) Leakage occurs when the pump starts after stopping for a period of time. This is mainly due to the solidification and crystallization of the medium near the friction pair, scale on the friction pair, and spring corrosion and blockage to lose the bullet.5) The pump shaft is too disturbed.

As several commonly used types, plunger pumps are important devices in electronic equipment and hydraulic systems. They have various advantages such as high rated pressure, good structure, easy operation, high efficiency, and convenient flow adjustment. So today, I will introduce to you the working principle of the plunger pump, the structure of the plunger pump and how to carry out the daily maintenance of the plunger pump.How the plunger pump worksThe plunger pump is an important device in the hydraulic system. It relies on the reciprocating movement of the plunger in the cylinder to change the volume of the sealed working chamber to realize oil absorption and oil pressure. The plunger pump has the advantages of high rated pressure, compact structure, high efficiency and convenient flow adjustment, and is widely used in high pressure, large flow and flow adjustment occasions, such as hydraulic presses, engineering machinery and ships.The plunger pump is a kind of reciprocating pump, which belongs to the volume pump. Its plunger is driven by the eccentric rotation of the pump shaft to reciprocate. Its suction and discharge valves are one-way valves. When the plunger is pulled outward, the pressure in the working chamber decreases, and the outlet valve closes. When the pressure is lower than the inlet pressure, the inlet valve opens and the liquid enters; when the plunger is pushed inward, the pressure in the working chamber increases, and the inlet valve closes. When the pressure is higher than the outlet pressure, The outlet valve opens and the liquid is discharged. When the drive shaft drives the cylinder to rotate, the swash plate pulls or pushes back the plunger from the cylinder to complete the oil suction and discharge process. The oil in the working chamber formed by the plunger and the cylinder hole communicates with the suction chamber and the oil discharge chamber of the pump respectively through the oil distribution plate. The variable mechanism is used to change the inclination angle of the swash plate, and the displacement of the pump can be changed by adjusting the inclination angle of the swash plate.Piston pump structurePiston pumps are divided into two representative structural forms: axial piston pumps and radial piston pumps; since radial piston pumps are a new type of high-efficiency pump with relatively high technical content, with the continuous development of hydraulic technology, Radial piston pumps will inevitably become an important part of the application field of piston pumps.Piston pump maintenanceThe swash plate axial piston pump generally adopts the form of cylinder rotation and end face flow distribution. A friction pair consisting of a bimetal plate and a steel oil distribution plate is inlaid on the end surface of the cylinder body, and most of them adopt the method of plane flow distribution, so the maintenance is relatively convenient. The oil distribution plate is one of the key components of the axial piston pump. When the pump is working, on the one hand, the high-pressure oil in the working chamber pushes the cylinder to the oil distribution plate; on the other hand, the oil film pressure between the oil distribution plate and the cylinder forms a The hydraulic reverse thrust of the cylinder keeps the cylinder away from the oil distribution plate. The design hydraulic pressure Fn of the cylinder to the oil distribution plate is slightly greater than the hydraulic reverse thrust Ff of the oil distribution plate to the cylinder, that is, Fn/Ff=1.05~1.1, so that the pump works normally and maintains a high volumetric efficiency.

advantage:1. The range of high and low temperature resistance is greatly enhanced, the low temperature can reach -200°C, and the high temperature can reach about 300°C, which is unimaginable for the previous forms of sealing.2. The coefficient of friction is lower. Although the sealing material of the gray ring and step seal may be the same as that of Variseal, the coefficient of friction is lower, but the coefficient of friction of the same material will be lower, especially when the working pressure is high. , the difference is very significant.3. Longer service life, if the material is commonly used by Variseal: the storage life of filled PTFE and stainless steel is theoretically unlimited, and the service life is longer than other forms of seals, and it is also unlimited under some working conditions Period, which is very important for some special-purpose cylinders.4. Resistant to high pressure and ultra-high pressure. Generally, standard designed pan-seal rings can withstand a pressure of 20-30MPa. By changing the design parameters, it is easy to withstand a pressure of more than 100MPa.5. Under high and low pressure, the leakage is small. Variseal rings can have good sealing performance under high and low pressure, while other forms of sealing are either good in high pressure resistance or low pressure resistance, and it is difficult or even impossible to have good high pressure resistance and low pressure resistance at the same time. achieve.6. The installation groove is small, and the standard size of the installation groove is the same as that of O-rings of the same level.shortcoming: 1. The installation groove is generally open or semi-open, especially for small-diameter cylinders, which must be open or semi-open, which may increase the cost for the design, manufacture and installation of the cylinder.2. The manufacturing process of seals is turning forming, the production efficiency is low, and the manufacturing cost is higher than that of ordinary seals, so the purchase cost of seals will be higher.Typical application conditions:1. High temperature sealingModern industrial cylinders require high-temperature cylinder seals in many places, such as pressure casting cylinders, metallurgical cylinders, kiln cylinders, automotive engine seals, etc., and the maximum temperature reaches about 300°C.2. Cryogenic sealingLiquefied nitrogen, liquefied petroleum gas, liquefied carbon dioxide, liquefied oxygen, etc. are sealed, and the lowest temperature can reach -200°C.3. High pressure sealingSuper-large tonnage presses, high-pressure water cutting machines, air compressors, etc., with a maximum pressure of 400MPa.4. High-speed sealingHigh-speed shaft, the speed can reach 30-40 meters per second. High-speed reciprocating oil cylinder, the telescopic speed can reach 15-20 meters per second.5. Special working medium sealHigh temperature water vapor, sea water, brake fluid, acid and alkali, etc.6. Low frictionA typical example is a servo cylinder.7. Long life sealWind power variable pitch cylinder, building shock absorption cylinder.8. Long oil cylinder sealTypical examples are crane cylinders and stacker cylinders.9. Hygienic and safe sealingAt present, the sealing of food and medicine contact has basically adopted the Pansythen ring.10. Quick response cylinderThe installation groove of the seal is small, the structural parts of the oil cylinder can be lighter, and the frictional resistance is small at the same time, which can greatly improve the dynamic performance of the oil cylinder and create a better quick-response oil cylinder.

Variseal seal and comparison with O and U ringsVariseal, the word comes from the transliteration of "Variseal", which means composite seal and combined seal, usually refers to spring energy storage seal, and is the abbreviation of spring variseal (spring composite seal)."Fanseal" itself is a transliteration of "composite seal", so there is no need to add the word "seal" after "Fanseal". If you call it according to the custom, you can add this word. Of course, it is better to directly say "spring energy seal" according to Chinese.The figure on the right shows the typical structure of Variseal, which is divided into two different parts, the inner and outer parts. The outer seal body is made of special functional plastic, and the inner part is made of stainless steel spring made of special material.The materials of the seal body and the spring are different due to different working conditions and working media. Generally, the materials of the seal body include: pure tetrafluoroethylene, filled tetrafluoroethylene, ultra-high molecular weight polyethylene, polyimide, polyether ether ketone, etc. The materials of stainless steel springs generally include SUS301, SUS304, SUS316 and SUS718.The external seal body is in contact with the two surfaces to be sealed and acts as a seal, so it requires low friction coefficient, high strength, wear resistance, working medium resistance, and high temperature or low temperature resistance in the working environment.The internal stainless steel spring provides pressure for the external seal body, so that the seal lip is always tightly pressed against the sealing contact surface to prevent leakage, especially when the internal pressure is low, zero pressure or even negative pressure, The spring is the only source of sealing pressure. The requirements for the spring are relatively simple: high and low temperature resistance to the environment, corrosion resistance, and relatively constant elastic force. Although these requirements are not many, they are not easy to achieve. The material, process and shape of the spring have high requirements.Variseal is a sealing form developed in recent years. Like the combined seals such as Gray ring and Step seal, it fully utilizes the superior performance of each component material, so that the overall performance far exceeds any single material seal. Compared with previous seals in various forms, it has both significant advantages and obvious defects.