Needle valve performance parameters and materials used
Performance parameters and materials of needle valve:
One, nominal diameter
Nominal size DN is the numerical size of all pipe fittings in the piping system to distinguish those parts represented by thread or outside diameter. Nominal size is a rounded number used as a reference and is not completely equivalent to the number of machining dimensions.
Nominal sizes are marked with the letters "DN" followed by a numeric symbol. If nominal diameter is 250mm, it shall be marked DN250.
Two, nominal pressure
Nominal pressure PN is a pressure - related symbol expressed by Numbers, which is a convenient round integer for reference. Same nominal pressure PN value marked by the same nominal path!" All pipe accessories shall have the same connection size corresponding to the end connection type.
In China, when it comes to nominal pressure, the unit of measurement is usually given as "MPA" for the sake of clarity. In the United Kingdom, the United States and other countries, although the concept of nominal pressure has been included in the relevant standards, the British unit Class is still used in practice. There is no exact correspondence between nominal pressure and pressure level due to the difference in temperature reference. See table for a rough correspondence between the two.
The Japanese standard has a "K" system, such as 10K, 20K, 40K, etc. The concept of this pressure level is the same as that of the pressure level in the imperial system, but it is measured in metric.
Three, Pressure - temperature rating
The pressure-temperature rating of the needle valve is the maximum allowable operating pressure (z) expressed by the gauge pressure at the specified temperature. When the temperature rises, the working pressure is allowed to decrease.
Many countries have developed pressure - temperature rating standards for valves, pipe fittings and flanges. Pressure - temperature ratings, data for various materials.
The typical data of flow coefficient of needle valve and the factors that influence the flow coefficient
The value of flow coefficient varies with the size, form and structure of the valve. The flow coefficient of several typical valves varies with the diameter.
For needle valves of the same design, fluid flows through the valve in different directions. The value of the flow coefficient also changes. This change is usually due to different pressure recoveries. If the flow through the needle valve causes the disc to open, a circular diffusion channel between the disc and the body allows some pressure to be restored. The seat has a significant impact on pressure recovery when flow through the valve causes the disc to close.
For high pressure Angle valves, the flow coefficient is higher when the flow of the fluid makes the valve tend to close, because the diffusion cone of the seat restores the pressure of the fluid. The valve internal geometry is different, the flow coefficient curve is also different.
The internal pressure recovery mechanism of the needle valve is the same as that of the pressure loss caused by contraction and diffusion of the venturi. When the pressure drop inside the needle valve is the same, if the pressure inside the valve can be restored, the flow coefficient value will be larger, the flow will be larger. Pressure recovery is related to the geometry of the valve chamber, but more depends on the design of the disc and seat.
Needle valves are commonly used
Needle valves are usually composed of the body, cover, disc (gate), seat, stem, hot plate, packing and drive device (handwheel, gearbox or pneumatic, electric device, etc.).
The material of the body and cover in the needle valve is the shell material (also known as the main body material), gate (disc), ball, seat, stem, sealing seat is often called inner parts, in addition to fasteners, seals, etc.
According to shell/main body material classification, needle valve can be divided into:
1. Metal material needle valve: such as carbon steel valve, alloy steel valve, stainless steel valve, cast iron valve, titanium alloy valve, monel valve, copper alloy valve, aluminum alloy valve, lead alloy valve, etc.
2. Metal body lined needle type valve: such as lined rubber valve, lined fluorine valve, lined lead valve, lined plastic valve, lined enamel valve.
3. Non-metallic material needle valve: such as ceramic valve, glass valve, plastic valve.
Needle valve material selection
Under normal circumstances, needle valve material should be selected according to its parameters and material performance according to this standard, and should comply with the provisions of the relevant product standards. Other materials with properties not lower than those specified in this standard or agreed upon by both parties in the contract may also be selected.
The technical requirements for needle valves in special cases are as follows:
1. Gray cast iron needle valve
Used for grey cast iron valves with water, steam, air, gas and oil at nominal pressure pN≤ 1.0mpa and temperature -10 ~200℃.
2. Malleable iron needle valve
Used for malleable cast iron valves with nominal pressure pN≤2.5MPa and temperature -30 ~300℃ medium such as water, steam, air and oil.
3. Spheroidal ink-cast iron needle valve
Used for spheroidal graphite cast iron valves with nominal pressure pN≤ 4.0mpa and temperature -30 ~350℃ medium such as water, steam, air and oil.
4. Needle valve of copper alloy
Used for water, sea water, oxygen, air, oil and other media with nominal pressure pN≤ 2.5mpa, as well as copper alloy valves with vapor medium with temperature of -40 ~250℃.
5. Carbon steel needle valve
Used for carbon steel valves of water, steam, air, hydrogen, ammonia, nitrogen and petroleum products with nominal pressure pN≤32.0MPa and temperature -30 ~450℃.
6. High temperature steel needle valve
Used for high temperature steel valves with nominal pressure pN≤ 16.0mpa and temperature less than or equal to 550℃ for steam and petroleum products.
Low temperature steel needle valve
Used for low temperature steel valves of ethylene, propylene, liquid natural gas and liquid nitrogen with nominal pressure pN≤ 6.4mpa and temperature higher than or equal to -- 196℃.
8. Stainless and acid-proof steel needle type valve
Used for nominal pressure pN≤6.4MPa, low temperature