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Correct selection of mechanical seal is a key to prevent pump leakage

by:Lepu Seal     2020-04-04
Seal mechanical seal is the use of the basic elements of two surfaces friction between the principle of operation, to achieve the purpose of sealing. Rotating seal face installed in the pump shaft, the fixed seal face installed in the gland. Due to a sealing surface is in motion, and the other a sealing surface is stationary, so will the class is called dynamic sealing seal. The latter two commonly used static seal leakage pathways, because there is no relative movement between the two parts. This part of the seal are usually called three seal, the sealing material for gasket or compatible with process fluid sealing ring (o-ring). In older seal design, surface of revolution in the secondary seal have certain gap, but on the main shaft movement before and after, so easily lead to wear and premature failure. In the new seal design, however, secondary seal in the static state, thus can avoid wear corrosion problems on the spindle. In the normal operation of pump, rotating between surface and the surface of the stationary for stuffing box produced by the liquid pressure and keep it in a sealed condition, when starting and stopping, stuffing box pressure produced by spring pressure to maintain, Can even by spring pressure to replace) 。 Most of the design of the mechanical seal with soft materials to make the surface of revolution, the rotating friction on the surface of the harder still. Over the years, the combination of the most common is the use of carbon materials as a surface of revolution, to make it run on the surface of the ceramic stationary. This kind of material is still in common use, but still face is select stainless steel or more rigid materials, such as tungsten carbide and silicon carbide. No matter use what material, in a word between the contact surface must be kept in a layer of liquid membrane, in order to play the role of lubrication. However, in the packing box, use the spring load and the way of the combination of liquid pressure, can have very good sealing effect between the sealing surface. But sealing pressure is too high, will affect the interface formed between the liquid membrane, increase heat and premature wear and tear. If sealing pressure is too low, contact surface between the gap increases, easy to cause liquid leakage. Seal manufacturers are constantly trying to improve the contact area of straightness, they adopt special grinding polishing plate. Then, using monochromatic light grating surface of the test. From this point of view, on the sealing contact surfaces must be handled with care, and in strict accordance with the installation instructions, ensure the sealing surface protection and correct properly in place, it is very important. Seal the flexibility to choose the main shaft of axial and radial motion to maintain flexibility with spring, to ensure the sealing between the contact surface. However, can only provide a certain degree of flexibility. Pump mechanical condition and its length diameter ratio ( A spindle diameter and the ratio of the extension length measure, the lower the ratio, the better) The reliability of sealing plays an important role. Seal the flexibility of general by a large main spring and a series of small spring or corrugated ensure sealing device. Chemical industry adopted by the traditional seal design, its sealing pressure is applied to rotary surface, this seal is called rotating seal, because the spring or corrugated sealing device with the spindle rotation. Is new design, its spring or corrugated sealing device installed on stationary base. On the mechanical seal, the above two types of seal are very common, so that have certain flexibility for the installation. Early design of many mechanical seal using a single large spring around the main shaft is arranged, in the process of pump starting, can provide strong sealing force for sealing surface. Sealing effect depends on the rotation of the spindle to tighten the spring rolls. To many corrosive strong application field, the general design is to use metal bellows seal device. The corrugated pipe is made up of a series of metal plate welded together, forming a seal to prevent leakage of ripple. Using this device can make the sealing surface sealing pressure between more uniform, and do not need to increase the secondary seal on the seal, such natural won't produce any corrosion wear phenomenon. In general, the main sealing pressure depends on the stuffing box itself, but spring and bellows compensation pump during starting and stopping an insufficient pressure of spindle motion, make the sealing surface sealing always maintain pressure. Corrosion and wear problems due to many reasons, such as including bearing tolerance, shaft end clearance, vibration and spindle deviation, can make the pump spindle radial and axial movement. In addition, because it is very hard to maintain absolute parallel between contact surfaces, so the mechanical seal is produced inside the mobile also is very normal. This kind of mobile is often due to the equipment and installation of tolerance, thermal expansion, piping stress that caused by improper or spindle debugging. In order to keep each other between the sealing surface, spring between the mechanical seal and motor spindle constant adjustment. When the rotation surface using artificial rubber seal, between the spindle and the elastomer will back and forth on the spindle motion. Will this repeat friction, abrasion on the main shaft of anti-corrosion materials, loss of the spindle of the oxide film layer, eventually formed on the surface of the spindle of the friction wear grooves, cause liquid leakage from the groove, and add the necessary maintenance workload or even replace the spindle. In order to solve this problem, generally in the packing box installed a replaceable shaft sleeve. However, the only permanent solution to solve the problem of corrosion and wear is to remove the internal dynamic seal. Now, most of the main seal factory production of corrosion and wear type seal, in order to prevent the corrosion and wear of pump parts.
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