Stem is driven open-close part makes an important part of a valve opening and closing, because the Industrial Valves stem is movable parts. So it is most likely to produce leakage parts. Therefore, the stem seal for the valve is very important. Stem usually use compression packing. Compression packing refers to the pressure into the stuffing box around the valve stem seal soft material. Filler ACTS on the lateral pressure on the surface of the support if equal to or higher than the medium pressure, but also enough to make closed the leak on the surface of the transverse groove, the packing seal can impact on the media. Compression packing gland seal pressure generated by the packing to lateral expansion. If packing pressure of party work the same as the medium, is in the end of the packing pressure will produce the same pressure on the surface of the horizontal support. Tight, therefore, the packing gland, packing of lateral pressure often higher than the medium pressure to the packing gland of a pressure value, then automatically sealing effect. 1. Most of the compression packing compression packing due to considering the performance of the asbestos make use of its fiber as basic material. It is basically from the most media, the influence of temperature and time, is a kind of good conductors. Asbestos weakness is poor lubricity, so must add do not impede the performance of asbestos lubricant, such as graphite powder and mica powder. Because of the still has the permeability, the mixture will refill liquid lubricant. Ptfe has the minimum shrinkage rate, reduction rate is the lowest, and has the characteristics of low friction coefficient. For most of the corrosive medium has high KangFuXing can. Ptfe ethylene temperature - packing in the packing work Between 150 ~ 260 ℃. In this temperature range, it is a kind of high performance, multifunction stem packing. Flexible graphite has the characteristics of high temperature resistant, it also has a small friction coefficient and resistance to most corrosive medium, in the packing of the working temperature is 600 ℃, so the power plant, petrochemical and other department of the valves are used by the high temperature of flexible graphite packing. 2. Packing of stainless steel stem the corrosion of stainless steel stem, especially made of chrome 13 series steel stem, contact with the filler surface often from corrosion. The corrosion often happens before use storage stage, this is because the packing is saturated with water after water pressure test. If the corrosion will happen immediately put into use after water pressure test. In theory, in the wet packing of the stainless steel valve stem corrode, is due to the fact that the stem is surrounded by a filler surface is the result of deoxidization environment. This kind of environment influence the activation and passivation characteristic of the metal. Stainless steel oxide layer on the surface of the oxygen sensitive produced many small anode and the anode and the anode effect of residual blunt metal together, makes the metal internal generate galvanic effect. Usually used for packing of graphite as the anode material on the stem steel cathode field enhanced the galvanic current intensity, thus greatly contributed to the corrosion of corrosion to the original point. 3. Stem packing in the form of a squeeze packing squeeze packing suitable for the name of the o-ring kind of packing. This kind of packing is installed its lateral squeeze, with the aid of the elastic deformation of material to keep its lateral preload force. When the medium from the bottom into the packing chamber, packing to the valve stem and the space between the movement of turning, to plug the leak path. When packing chamber pressure to drop, packing and restore its original shape. Lip lip filler filler due to its lips soft, in the medium pressure will be close to the retaining wall and the lateral expansion of the expandable filler can be used in the compression packing, can't use relatively hard material. Lip packing shortcoming is its sealing function is only one direction. Most used to stem the lip of packing is made of pure ptfe or filled ptfe. But there have also been made to use fiber reinforced rubber or leather. Mainly used in hydraulic aspects. Most used for lip of the stem packing into a 'V'. So even in installation and easy to expand. Thrust pad thrust packing by packing ring or installed in the Industrial Valves cover and stem shoulder washer between the composition, the valve stem can make their axial movement relative packing ring. Stem seal can be the start of the auxiliary shaft seal picture such as live shrink packing to provide, also can be provided by the spring, the spring force stem shoulder to resist thrust packing, then the medium pressure can force the valve stem shoulder more closely contact with packing. Diaphragm valve stem seal diaphragm valve stem is made of flexible and pressure Industrial Valves to seal the cover, the cover is connected to close the valve stem and pieces. This kind of seal failure, as long as the diaphragm don't can avoid any medium through the valve stem emission into the atmosphere. Diaphragm material varies according to the purpose of the valve, the available stainless steel, plastic or rubber, etc.
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