What is a dynamic seal
Dynamic Sealing, it refers primarily to stem seal. Not in the media with the valve stem leakage campaign is the center of the valve dynamic seal issue.
1) Fill the form letter
At present, the dynamic seal valves, mainly to fill letter. Filler is the basic form letter:
(1) gland -
This is the most used form.
While many of the details of the same distinction. For example, from the clamping bolt, the bolt can be divided into T-shaped (for pressure ≤ 16 kg / cm2 of low pressure valves), the double-headed bolts and bolts of living. From the gland, can be combined and the overall style.
(2) clamping nut -
This form, shape, small size, but the clamping force restricted use only in the small valve.
2) Fill
Fill letter in order to stem direct contact with the filler and full of filler letter to prevent the media leakage. To fill the following requirements:
(1) sealing properly;
(2) corrosion-resistant;
(3) the friction coefficient small;
(4) to medium temperature and pressure.
Common filler:
(1) Asbestos Pan-gen: asbestos Pan-gen, temperature and corrosion resistance are very good, but when used alone, poor sealing effect, always dipping or surcharge other materials. Oil asbestos Pan-gen: it forms the basic structure of the two, is a torsion system, and the other is for guitar. There are also circular and square.
(2) Pan-gen PTFE weaving: PTFE fine weaving with the Pan-gen, excellent corrosion resistance, but also for the cryogenic medium.
(3) rubber O-ring: in the low-pressure condition, sealing well. Temperature restricted use, such as natural rubber can only be used in 60 ℃.
(4) plastic molding filler: General Sanjianshi made, but also made other shapes. PTFE plastic used to more, but also using nylon 66 and nylon 1010.
Moreover, the use of units according to their own needs, and often explore effective form filler. For example, in the 250 ℃ steam valve, used asbestos Pan-gen turn again and again and lead a lap, steam leakage situation will be reduced some valves, constantly changing medium, such as asbestos and PTFE Raw Pan-gen band together and sealing effect will be better.
In order to reduce the friction on the stem, and some occasions, and molybdenum disulfide (M0S2) or other lubricants.
Currently, the new packing is carried out to explore. For example, polyacrylonitrile fiber impregnation by the PTFE emulsion, and the pre-oxidation, in the mold sintering suppression, can be excellent sealing properties forming filler; Another example is the use made of stainless steel sheets and asbestos packing waveform, high temperature, high pressure and corrosion.
3) Bellows Seal
Along with the chemical industry and the rapid development of the atomic energy industry, flammable, explosive, poisonous and radioactive substances increased, the valve seal with more stringent requirements, and some have been unable to use occasions packing seal, resulting in a new enclosed form - bellows seal. This sealed without filler, also known as a packing seal.
The two ends of corrugated pipe, and other parts of welded shut. When stem movements, stretching bellows, as long as the bellows itself is not leaking, media would not be able to Yi Chu. For the sake of insurance, often using corrugated pipe and fill the double seal.
What is a static sealing
Static seal, which usually refers to surface between two static sealing. Seal approach is the use of washers.
1) gasket materials
(1) non-metallic materials: such as paper, linen, leather, asbestos products, plastics, rubber.
Paper, linen, such as leather, nonporous and easy to infiltrate, use should be dipping oil, wax or other anti-permeability material. General valve rarely used.
Asbestos products, has asbestos belt, rope, sheet rubber and asbestos panels. Which asbestos rubber plate structure is dense, pressure performance and heat resistance is also very good, in the valve and the valve itself and the pipe flange connection, the use of very wide.
Plastic products, a very good corrosion resistance, also more common use. Variety is polyethylene, polypropylene, soft PVC, Teflon, Nylon 66, Nylon, such as 1010.
Rubber products, soft texture, all kinds of rubber were certain acid and alkali resistance, oil resistance, water-resistant capacity.
Variety natural rubber, styrene-butadiene rubber, nitrile rubber, neoprene, iso rubber, polyurethane rubber, fluorine rubber.
(2) Metal: Generally speaking, metal materials high strength, heat resistance strong. But this does not lead, it only admitted dilute sulfuric acid-resistant properties. Common varieties are brass, copper, aluminum, low-carbon steel, stainless steel, Monel alloy, silver and nickel.