First, mechanical seal under high pressure

Mechanical seal operating pressure exceeds 4 ~ 5MPa That belongs to the high-pressure seal range. Under high pressure conditions, due to excessive seal face value than the pressure, causing the end face of the heat, thereby undermining form a liquid film, resulting in abnormal wear. High pressure also make friction deformation and rupture. High pressure seal generally balanced structure, so face pressure in an appropriate range. But given the seal of reliability, balance coefficient increases can not be unlimited, so in some cases despite the use of balanced structure, but face pressure still may be larger. Balanced structure alone is difficult to meet the requirements, this situation can be more controlled membrane end mechanical seal or mechanical seal.

Second, the mechanical seal at high temperatures

Under normal circumstances, the temperature of the medium exceeds 120 ℃ that is considered to be high-temperature seal. In this case the presence of the main problems of mechanical seals are:

(1) Due to the friction face temperature, resulting gasified liquid film between the seal faces, the friction coefficient increases, increased wear, temperature increase, sealing ring thermal deformation or thermal cracking and failure;

(2) Mechanical seals in the secondary seal materials are generally rubber or PTFE, due to the long time in high temperature environments, easy to aging and decomposition, resulting in seal failure;

(3) An elastic element under high temperature mechanical seal easy to produce fatigue and creep, seal failure;

(4) High-temperature corrosion of metallic materials will increase, shortening the life of the mechanical seal.

To ensure the normal operation of mechanical seals in high temperature environment, you can take the following measures.

1. To increase the cooling mechanical seal flushing device.

2. Select the high-temperature materials, use of different materials depending on the operating temperature. Nitrile rubber upper temperature limit of 80 ℃, silicone rubber and fluorine rubber is 200 ℃, PTFE 250 ℃.

In addition, the mechanical seal friction nonmetallic more made of graphite impregnated material, so they will have the choice of different types of impregnated graphite depending on the operating temperature. General Baptist Babbit graphite temperature range of less than 150 ℃, resin-impregnated graphite temperature range of 170 ~ 200 ℃, leaching of copper, aluminum, lead graphite can be used at less than 400 ℃ working conditions. Ring assembly should be used wherever possible material expansion coefficient close to prevent moving at a high temperature ring and ring seat loose connection.

3. Select the metal bellows mechanical seal. Metal bellows seal used in recent years many in high temperature sealing, and achieved good results. In this kind of mechanical seal, the metal bellows mechanical seal replaces the ordinary in spring, eliminating the need for secondary seal ring, ring compensation when required to overcome the friction and wear of the shaft, so use at high temperatures, generally You can achieve good results.

Third, the mechanical seal at low temperatures

In the refining and chemical apparatus, medium transport generally have low exclusion of small, poor lubrication, easy gasification characteristics, and a lot of endothermic gasification medium, so that the ambient temperature drastically reduced, resulting in condensation of water vapor in the air, lead to the end face and its surrounding ice, the end face of the fitting lax cause leakage. At the same time, due to poor lubrication, Friction generated more heat, if not timely transfer, will definitely increase gasification end face, resulting in a vicious cycle, accelerating early failure of the sealing surface. In addition, the low-temperature sealing secondary seal stiff at low temperatures and can lead to loss of elastic leakage.

Low temperature sealing, in addition to select the appropriate secondary seal the material, but also pay attention to the following points.

1. Improved sealing structure and the correct choice of friction material. Practice has proved that the stationary ring surface arc-shaped groove may be formed to open hydrodynamic seal, increase fluid film bearing capacity, improving end face lubrication, prolong the working life of the mechanical seal. In terms of the end face of the pairing, a M106K Graphite Tungsten Group (ie dynamic and static ring material) is generally superior to other materials because of its lubricating, low friction coefficient, thermal conductivity better.

2. Choose the appropriate face pressure. Due to the low temperature sealing end face poor lubrication, easily vaporized, icing, so the premise of ensuring reliable sealing, end may be appropriate to reduce the pressure ratio. General mechanical sealing pressure than the recommended value of 0.29 ~ 0.59MPa, the lower limit of the low-temperature sealing desirable. Metal bellows mechanical seal, since no axial friction ring, face pressure even below the lower limit.

3. Process to take appropriate measures. Such as to minimize the media's moisture content; maintaining the sealed chamber pressure is relatively stable; as a cooling device with a flushing; before the device starts to appropriate parts of the mechanical seal preheating.

Fourth, the mechanical seal at high speed

When the speed exceeds 3 000r / min or friction of the line faster than 25m / s, and it can be regarded as high-speed sealed. At high speeds, friction end face due to the linear velocity is large, heat generated by friction and more, at this end face film is not easy to form, increased wear.

High speed also easy to cause vibration of the rotating ring, and subject to greater centrifugal force, is not conducive to the formation and maintenance of film between the end face. So at a high speed in order to reduce the effect of centrifugal force and vibration, should minimize moving parts, with spring still structure. It can also enhance the friction face of cooling and lubrication. It may also choose [PV] the value of high friction material, reducing the contact width of the end surface, or a controlled membrane mechanical seal.

In recent years, a differential ring mechanical seal is also called high-speed devices in the applications. Since the middle of the ring at the original movement joined a differential ring friction linear velocity can be reduced by half, and achieved good results.

Fifth, the mechanical seal corrosive environment

Some mechanical seals in corrosive environments, then not only pay attention to the mechanical seal in the corrosion resistance of each part in itself, but also to prevent their combination together electrically coupled phenomena that may arise. Mechanical seal in corrosive environments, in the selection should pay attention to the use of corrosion-resistant materials. In addition, you can use externally mounted mechanical seal. Particularly corrosive prone to accidents that can double seal, the introduction of isolation was to protect them.

Sixth, the mechanical seal particulate media under

Some mechanical seal may work in a medium containing solid particles, the solid particles into the friction when the end surface, it is easy to produce severe wear, resulting in failure of the seal faces quickly. Additionally solid particles may cause ring seals can not be moved axially, so that ring can not float, loss of compensatory cause mechanical seal failure. This more effective approach is to add an external flushing device. Since the fluid pressure into the sealed chamber is higher than the medium pressure in the sealed chamber, it can effectively prevent particulate media into the sealed chamber. Also you can use double mechanical seal, in the middle of the sealed chamber sealed liquid is added. You can also use outside-mounted mechanical seal.

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