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From the point of view of convenience, fast connectors have appeared in the fluid system. Fast joint is a fluid connection mechanism which can realize fast connection and disassembly assembly without using tools….
Many valves can adapt to a variety of working conditions,but if the selection of valve materials is not reasonable,the performance and service life of the valve will be greatly reduced.First of all,according to the range of use of various valve materials,we can make it play a good performance.
Material for body,bonnet and disc
Valve body,cover and disc are the main parts of the valve.They are directly subjected to medium pressure.The materials used must meet the requirements of”pressure and temperature grade of the valve”.
Commonly used materials are as follows:
1 gray cast iron
Gray cast iron is suitable for medium such as water,steam,air,gas and oil,whose nominal pressure PN is less than 1.0 MPa and temperature is-10~200~C.
Common grades of gray cast iron:HT200,HT250,HT300,HT350.
2 malleable cast iron
It is suitable for water,steam,air and oil medium whose nominal pressure PN is less than 2.5 MPa and temperature is-30-300 C.
3 Ductile Iron
It is suitable for medium such as water,steam,air and oil with PN less than 4.0 MPa and temperature ranging from-30 to 350 C.
Common brands:QT400-15,QT450-10,and QT500-7.
4 acid-resistant High Silicon Ductile Iron
It is suitable for corrosive media whose nominal pressure PN is less than 0.25 MPa and temperature is lower than 120 C.
5 carbon steel
It is suitable for medium such as water,steam,air,hydrogen,ammonia,nitrogen and petroleum products whose nominal pressure PN is less than 32.0 MPa and temperature is-30-425 C.
Common grades:WC1,WCB,ZG25 and high quality steel 20,25,30 and low alloy structural steel 16Mn.
6 copper alloy
It is suitable for water,sea water,oxygen,air,oil and steam media with PN<2.5 MPa and temperature-40-250 C.
Common brands:ZGnSn10Zn2(tin bronze),H62,Hpb59-1(brass),QAZ19-2,QA19-4(aluminum bronze).
7 high temperature copper
It is suitable for steam and petroleum products whose nominal pressure PN is less than 17.0 MPA and temperature is less than 570 C.
8 low temperature steel
It is suitable for medium such as ethylene,propylene,liquid natural gas and liquid nitrogen with nominal pressure PN<6.4Mpa and temperature(-196 C).
9 Stainless acid-resistant steel
It is suitable for medium such as PN<6.4Mpa,nitric acid and acetic acid at temperature<200 C.
ZG0Cr18Ni10<Nitric Acid Resistance>
ZG1Cr18Ni12Mo2Ti<Acid and Urea Resistance>
Relation between Valve Material and Temperature
Sealing surface material
1 Soft Material
Rubber(including butadiene rubber,fluorine rubber,etc.)
2 Hard Sealing Material
Copper alloy(for low pressure valves)
Chromium stainless steel(for ordinary high and medium pressure valves)
Stellite alloy(for high temperature and pressure valves and strongly corroded valves)
Nickel-based alloys(for corrosive media)
During the opening and closing process of the valve,the stem bears tension,pressure and torsion forces,and contacts with the medium directly.At the same time,there is relative friction movement between the stem and the filler.
Therefore,the stem material must be guaranteed to have sufficient strength and impact toughness,corrosion resistance,scratch resistance and good workmanship at the specified temperature.
1 carbon steel
A5 common carbon steel is generally used in water and steam medium with low pressure and medium temperature not exceeding 300 C.
When used in medium pressure and medium temperature not exceeding 450 C for water and steam medium,35 high quality carbon steel is generally selected.
2 alloy steel
40Cr(chromium steel)is generally used in medium pressure and high pressure media,such as water,steam and petroleum,where the medium temperature does not exceed 450 C.
38CrMoALA nitriding steel can be used in high pressure and medium temperature not exceeding 540 for water,steam and other media.
25Cr2MoVA chromium-molybdenum-vanadium steel is generally used in steam medium with high pressure and medium temperature not exceeding 570 C.
3 Stainless acid-resistant steel
For medium and high pressure non-corrosive medium and weak corrosive medium with medium temperature not exceeding 450 C,1Cr13,2Cr13 and 3Cr13 stainless steel can be selected.
When used in corrosive medium,stainless acid-resistant steel such as Cr17Ni2,1Cr18Ni9Ti,Cr18Ni12Mo2Ti,Cr18Ni12Mo3Ti and precipitation hardening steel PH15-7Mo can be selected.
4 heat resistant steel
4Cr10Si2Mo martensitic heat resistant steel and 4Cr14Ni14W2Mo austenitic heat resistant steel can be used for high temperature valves with medium temperature not exceeding 600 C.
Stem nut material
In the process of opening and closing the valve,the stem nut bears the axial force of the valve stem directly,so it must have certain strength.
At the same time,it and the valve stem are threaded transmission,requiring small friction coefficient,no rust and avoid biting phenomenon.
1 copper alloy
Copper alloy is one of the most widely used materials because of its low friction coefficient and non-rusting.
ZHMn58-2-2 brass can be used for low pressure valves with Pg<1.6Mpa.
For Pg16-6.4Mpa medium pressure valves,ZQAL9-4 tin-free bronze can be used.
ZHAL66-6-3-2 brass can be used for high pressure valves.
When copper alloy is not allowed to be used in working conditions,high quality carbon steels such as 35 and 40,stainless acid-resistant steels such as 2Cr13,1Cr18Ni9 and Cr17Ni2 can be selected.
Working conditions are not allowed to refer to the following circumstances.
For electric valves,stem nuts with melon clutch need heat treatment to obtain high hardness or surface hardness.
The working medium corrodes copper.When choosing steel stem nuts,special attention should be paid to the screw thread biting phenomenon.
On valves,packing is used to fill the space in the packing chamber of the valve cover to prevent medium leakage through the stem and the packing chamber space of the valve cover.
1 soft filler
Vegetable packing is cheaper and is often used in low-pressure valves below 100 degrees Celsius.
Mineral fillers can be used in valves at 450-500 C.
The filling medium temperature of rubber O-ring is generally limited to below 60 C.
The packing on the high temperature and high pressure valve is also compacted by pure asbestos and flake graphite powder.
2 rigid filler
Botanical substances,such as hemp,flax,cotton,jute,etc.,or minerals,such as asbestos fibers,or yarns woven by asbestos fibers with metal wires inside and graphite powder outside,also have compacted fillers and flexible graphite fillers developed in recent years.
Temperature Selection of Common Packing