To prevent the working fluid leaked from the pump or to prevent external impurities or air intrusion into the internal pump devices or measures as sealing, be sealed medium is generally liquid, gas or dust.
Leakage caused by two main aspects: First, seal the surface of a gap. Second, there is pressure difference on both sides of sealing parts, to eliminate or reduce any of these factors can prevent or reduce leakage to achieve the purpose of sealing. Pump design pressure and the use of pressure is an objective can not reduction, so the pump sealing the solution is to eliminate or reduce the gap between the sealing surface. This space includes the space between the sealing surface and seal the internal space Bunsen.
Pump seal is divided into two categories: one for static seal, one type dynamic seal. Static sealing gasket seal usually, O-ring seal, thread sealing type. Sealing is mainly soft packing seal, oil seal seal, labyrinth seals, spiral seals, dynamic seals and mechanical seals.
Gasket Seal
Static sealing gasket is the basic element centrifugal pump, using a wide range. Gasket Selection mainly based on pumping medium, temperature, pressure and corrosion and other factors. When the temperature and pressure is not high generally use non-metallic gasket; in pressure at high temperatures, use non-metallic gaskets and metal combination. The application of non-metallic gaskets in the pump is most common in the material is generally paper, rubber and PTFE. When the temperature does not exceed 120 ℃, pressure 1.0Mpa below, generally used in the green shell mold of paper or paper pads. If the transmission medium is oil, the temperature at -30 ~ 110 ℃, the general use anti-aging properties of NBR better. When the transmission medium at -50 ~ 200 ℃, choose more appropriate fluorine rubber. The reason is that oil heat, the mechanical strength is also its main features. In the chemical pump, because the transmission medium is corrosive, it is generally used as a gasket material PTFE. With the pump more and more widely used in the field, the medium to be more and more species, so the choice of gasket material should be access to relevant information or to make the right choice after the experiment.
Gasket failure due mainly to the following situations:
1, acting on insufficient pressure on the gasket. As the sealing surface uneven micro there is always, sometimes also sealed a number of circular grooves machined surface, if the guarantee seal, the gasket must exert enough pressure to make it elastic or plastic deformation to occur fill these gaps. Pressing force of various gasket materials are usually the size of the sample in the gasket manufacturer or product description given, may decide by experiment. As the assembly will not meet the required compression force gasket or due to constant vibration of the running to make bolts loose Ershi pressing force reduction as a result of the aging of gasket material elastic deformation will cause the loss of original pad chip failure caused by leakage.
2, gasket material or the thickness of the uneven internal organization, and the use of cardboard with a crack or wrinkle, so that the formation of a gap gasket itself, when the role of force in the gasket on the gasket so that the elastic deformation produced by not completely filling these gaps, the leakage also inevitable.
3, gasket material incompatible with the transmission medium. As the pumps handle chemical products and chemical properties of diversity, as well as improve fuel combustion value or change the combustion of fuel in the resultant increase in the number of small amounts of additives into the fuel after the Ershi some properties change, so selection and distribution of media with suitable gasket material is not easy, and thus frequently occurs as incompatible Ershi erosion caused by gasket leakage phenomenon.
O-ring seal
Pump is commonly used in rubber O-ring. Because of its shape is very simple, thus creating simple and cheap, regardless of size O-ring of Zhengti the extent of its cross-section dimensions are small (Zhiyou millimeters) Suo Yi Weight 轻, consumption materials are few, Uses simple, installation, dismantling easy more prominent advantage lies in O-ring seal has a good ability to use a wide range. Static sealing pressure up to 100MPa or more seals are up to 30Mpa. Application temperature of -60 ~ 200 ℃, can meet a variety of media requirements. Therefore, the design of the pump to get more and more widely used.
O-ring was installed in the trench and between the sealing surface has a certain amount of compression, the resulting reaction force to be sealed smooth surface and trench bottom to the initial compressive stress. To play a role in sealing. When the liquid pressure increases sealing, O-ring deformation also increased and thus passed to the sealing surface of the pressure increases, increasing the role of seal. This is the O-ring seal has a good ability to reason.
Although the O-ring sealed and reliable, if not pay attention to conditions of use will leak, usually have the following situations:
1, install O-ring groove size tolerance, especially in the depth dimension is too large, so that after installation O-ring compression seal deformation effects of insufficient capacity. General O-ring compression deformation after installation should be 18% ~ 22%, and the section size is relatively large compression deformation is smaller than the section size is small relative deformation of compression is greater.
2, O-ring size of the nominal size range is too large and the actual installation, the formation of O-ring cross-section size reduction in tension after the work under the situation, resulting in insufficient deformation caused by leakage.
3, O-ring during installation due to the sealing surface of the imports is not chamfered or filleted smooth but will scratch and produce O-ring leakage.
4, O-ring seal material does not apply to media after the failure has been eroded. 5, O-ring use, after too long an aging deterioration, elasticity, after the failure, so when the device is generally overhaul O-ring replacement.
In addition, O-ring hardness, groove and the sealing surface roughness also affects the O-ring seal.
Thread Seal
Thread seal the pump there are two forms, one is threaded connection gasket seal, a filling is added economic thread sealing Both of these two small-diameter threaded connections for sealing occasions. Thread connection gasket sealing gasket seal is, but only from the thread to provide compression loads. The effect of sealing gasket itself in addition to the performance outside. Sealing surface roughness and with the screw hole location relative geometric accuracy of a great impact on the seal. On the gasket when the tightening screw pressing force is not only affordable, but also to withstand torque, so that deformation or even damage the gasket, so, when the gasket is non-metallic, generally apply only to low pressure of the occasion, if gaskets for the metal is used for pressure up to 30Mpa above.
Pump frequently used a plug, thread sealing is another form. Taking into consideration that a plug manufacturing economy generally can not play alone with thread seal, often with the students tape, sealants and other filler gap filling sealing thread. Pressure depends on its ability to manufacture precision thread and material, with silk thread hole blocking and has nothing to do with the form. Threaded hole and a plug either a "cone of the cone" or a "pillar of the cone," the same sealing effect, but use a different area. China currently uses two forms of the same. Affect the sealing effect of the common cause is when the bottom in the processing thread size is too large, so short of thread deformation, the top teeth wider, resulting in reduced sealing surface when the sealed pressure increases resulting from leaks, and even a plug extrusion. As the filler to be sealed leak caused by corrosion phenomena in the chemical industry pumps also occur, so the choice of filler is also sealed one of the factors considered.
Packing Seal
Will be full of compressibility and elasticity of the packing into the stuffing inside, relying on the axial compression force gland into the radial sealing force, and thus play a role in sealing. This seal is called packing seal, such as sealing filler filler. As the packing seal structure is simple, easy to change, low cost, to adapt to speed, pressure, medium broad and in the design of the pump are widely used. Transport medium at room temperature, the packing seal ring generally has its high-pressure chamber or the pump connected, or external pressure with a certain liquid media, can play a cooling, lubricating, sealing, or a flushing effect. As the packing seal is a contact seal, so there is bound to friction and wear problems. The friction and wear of the size, mainly on the packing gland of the pressing force. Pressure can improve the sealing effect, but it will increase power consumption and the wear sleeve, otherwise it will have a greater leakage. Therefore, in accordance with the size of leakage and leakage of the medium temperature of the gland to adjust the pressing force, if necessary, to fill replacement or supplement. Reasonable packing seal leakage generally 10-20ml/min. When the introduction of liquid from the outside world, should ensure that the liquid has good chemical stability, not pollution, the transport medium pump, not react with the medium and solid particles generated sediments, but also with a good impregnation of filler and long-lasting preservation, it can play a good and lasting seal.
Dynamic Sealing
Vice Expeller seal pumps stop running, vice impeller balancing pressure head produced by the main export of high-pressure liquid impeller in order to achieve sealing. Parking, the Deputy impeller does not work, it must also solve the parking with parking seal leakage may arise.
Vice impeller sealing simple, reliable sealing and long service life, operation can be realized leak, so impurities in the transport medium pumps often used. Vice impeller good seal is conditional, that exceed the allowable working pressure does not allow the working pressure. Once over, will have a serious leak. Working pressure is mainly due to changes in the pump suction pressure, so a by-impeller pump seal, pump inlet pressure must be made strict rules, or seal would be invalid. Since the form of sealed parking lot, after the failure easily found, this will not go into.
Screw Seal
Screw Seal Seal is a form of power, which is the axis or rotation axis of inclusion in the process put on a spiral groove, between the shaft and the sleeve filled with sealing medium. Axis of rotation to produce spiral groove similar to the role of pump delivery, thereby preventing leakage of sealing liquid. The sealing ability of the size and spiral angle, pitch, tooth width, tooth height, the role of tooth length and the gap between the shaft and sleeve size. Since no friction between the seal and therefore long life, but because of the structure of space limitations, the spiral length generally shorter, and therefore restricted its sealing ability. Slow down and use the pump, the seal will be compromised.
Labyrinth seal
Reasonable in the design, processing, sophisticated, well-equipped, high speed, the labyrinth seal works well. However, in practice, the resulting leakage is much analysis of the reasons are:
1 Sealing (such as shaft and bearing gland) with the gap too much, and this gap is inversely proportional with the sealing effect. With surface roughness, visible spiral car knife marks in some cases, the trend has increased the leak.
2, bearing interior volume of lubricant injected too much pressure over its overflow seal resistance.
3, oil or oil level gauge window installation location is incorrect, misleading the people on the correct amount of lubricant oil chamber judge.
4, in operation the increase of oil temperature to reduce viscosity and increase the possibility of leakage.
5, back to back hole size tank or small, or by other obstacles to block the liquid can be caused by leakage of a smooth return.
Seal Seal
Self-tight seal is a lip-shaped seal, its simple structure, small size, low cost, easy maintenance, low torque resistance, both to prevent media leaks, but also to prevent external intrusion of dust and other harmful substances, but also Wear has some ability to compensate, but impatience high pressure, it is generally used in low pressure situations. Seal should be installed in the manufacturing precision h8 ~ h9, the surface roughness of 1.6 ~ 0.8μm and the axis through the surface hardening treatment. Sealing medium should not contain solid particles and impurities, otherwise it will create rapid wear of seals and shaft seal failure Er Shi.
Shaft seal mechanical seal is the main method of modern, while the use of it is not easy to achieve do not leak, but to small, it is perfectly acceptable amount of leakage is possible. However, the operation of the pump is often embarrassing situation, then the mechanical seal failure because what is it?
1, mechanical seal material selection inappropriate. Mechanical seal material with the transport medium does not match. At work, quickly sealing elements corrosion, dissolution, or abrasion, thus losing the tightness. Therefore, according to the nature of transmission media options to ensure the mechanical seal material is its sealing function and a prerequisite for normal life.
2, the mechanical seal flush condition does not meet design requirements. In the transportation trade crystal or fine particles of the medium, there must be pressure and a certain flow of rinsesolution, Pize Qijiejingti Huozhe particulate Hui Jia Su seal pairs wear, Yijiyingxiang sealed Deputy wear Hou automatic Bu Changer Fashengxielou. Therefore, according to the nature of transmission medium not only to configure the appropriate flushing pipes, but also equipped with monitoring and regulating function of the instrumentation and equipment, ensure the fluid pressure and flow to meet the design requirements, in order to maintain the normal operation of mechanical seal, it is often ignored by the user.
3, each seal can bear the pressure is limited, because of the sealed chamber pressure measurement are not allowed to create a sealed cavity pressure exceeds the mechanical seal can withstand the pressure caused by leakage is also common seal failure of one of the reasons.
4, mechanical seal operating temperature can not exceed the specified value. Road in a cooling pipe design, often due to the cooling medium flow shortages at reducing the cooling effects; in the absence of cooling pipe in road design, the sealed nest cavity often keep the air as a result of mechanical seals in a dry friction condition. In both cases the movement will cause the mechanical seal Sealing temperature is too high to speed up wear and tear, resulting in seal failure.
5, single spring mechanical seal, it neglected the direction of rotation of the spring and pump rotor rotation direction of the right combinations occur. Or the design did not specify, or assembly of negligence, did not do as by rotating the rotor mechanical seal spring force increased but the opposite result, friction ring and static ring Vice insufficient pressure to form a leak.
6, bearing wear or serious damage, so serious shaft axial movement is also one of the reasons mechanical seal leakage. With the development of science and technology, new forms of seals and sealing materials continue, it is bound to the pump seal technology have a direct impact and promote. Long life, zero leakage of pumps will be promoted more and more places and applications.