• Common pressure ratings: In practical applications, common pressure ratings of DBB ball valves include 150LB, 300LB, 600LB, 900LB, 1500LB, and 2500LB.
• Pressure ranges under different standards: According to standards such as ASME B16.34 in American standards, the pressure ratings correspond to pound ratings. For example, 150LB corresponds to a nominal pressure of approximately PN1.6MPa, 300LB corresponds to a nominal pressure of approximately PN4.0MPa, 600LB corresponds to a nominal pressure of approximately PN10MPa, 900LB corresponds to a nominal pressure of approximately PN15MPa, 1500LB corresponds to a nominal pressure of approximately PN25MPa, and 2500LB corresponds to a nominal pressure of approximately PN42MPa.
• Pressure ranges for special applications: In some special industrial fields, such as deep-sea oil exploration, there may be a need for DBB ball valves with higher pressure requirements, and their pressure ratings may exceed 2500LB to meet the sealing and shut-off requirements under extreme working conditions.

1. CF3 (equivalent to 304L)
   • Chemical composition: It has a relatively low carbon content and is a low-carbon stainless steel, containing about 17 - 19% chromium and 8 - 12% nickel.
   • Characteristics: It has good corrosion resistance, especially strong resistance to intergranular corrosion, and is often used in valve application scenarios where welding is required and corrosion resistance is needed.
2. CF8 (equivalent to 304)
   • Chemical composition: It contains about 18 - 21% chromium and 8 - 11% nickel.
   • Characteristics: It has good comprehensive performance, with good corrosion resistance and mechanical properties, and is applied to valves dealing with general corrosive media.
3. CF3M (equivalent to 316L)
   • Chemical composition: Molybdenum is added on the basis of CF3, enhancing its corrosion resistance.
   • Characteristics: It has excellent resistance to pitting and crevice corrosion, and is used in valves in chemical, pharmaceutical and other environments with relatively strong corrosive conditions.
4. CF8M (equivalent to 316)
   • Chemical composition: It contains about 18 - 21% chromium, 8 - 11% nickel and 2 - 3% molybdenum.
   • Characteristics: It has strong corrosion resistance and good strength performance, and is widely used in various high-temperature and high-pressure valves dealing with corrosive media.

1. Parallel gate valve
   • Double-disc parallel gate valve: It has two gate plates connected by an expanding mechanism (such as a wedge, etc.). When closing, the two gate plates move towards the center and fit closely with the valve seat for sealing. It has good sealing performance and is suitable for media containing impurities, such as in sewage transmission pipelines.
   • Single-disc parallel gate valve: There is only one gate plate, and the sealing surface of the gate plate and the valve seat is parallel. It has a simple structure and low cost, and is commonly used in low-pressure and large-diameter pipelines, like the branch pipelines of urban water supply.
2. Wedge gate valve
   • Single-disc wedge gate valve: The gate plate is wedge-shaped. When closing, it descends along the slope of the valve seat and realizes sealing by the extrusion of the wedge structure. It has good sealing effect in high-pressure environments and is often used in high-pressure transmission pipelines in the petrochemical industry.
   • Double-disc wedge gate valve: It consists of two gate plates and a wedge in the middle. When closing, the wedge makes the two gate plates expand to both sides and seal with the valve seat. It can compensate for wear and prolong the service life, and is suitable for industrial pipelines that are frequently opened and closed, such as the steam transmission pipelines in power plants.

Classified by the structure form of the valve stem

1. Above-ground stem gate valve: The valve stem nut is on the valve cover or bracket, and the lifting and lowering of the valve stem can be seen 直观地. It is convenient to judge the opening and closing state of the valve, and it is widely used in water supply and drainage systems, such as the fire-fighting water system in buildings.
2. Non-rising stem gate valve: The valve stem nut is inside the gate plate, and the valve stem rises and falls with the gate plate. The movement of the valve stem cannot be seen from the outside. It has a relatively low overall height and is suitable for occasions with limited installation space, like underground sewage discharge pipelines.

1. Design Standards for Corrosion Resistance (such as NACE MR0175)
   • In corrosive environments such as in the petroleum and chemical industries, valves face serious corrosion threats. The NACE MR0175 standard is for the material requirements to resist sulfide stress corrosion cracking in the petroleum and natural gas industries. For Trunnion Mounted Ball Valves, the material selection for components such as the valve body and valve stem should comply with this standard.
   • For example, in a medium environment containing hydrogen sulfide, the materials need to have the ability to resist sulfide stress corrosion cracking. Meanwhile, the surface treatment of the valve is also important. For example, anti-corrosion coatings or linings are used to prevent corrosive media from directly contacting the base material of the valve and extend the service life of the valve.

1. Design Standards for Low Temperature Working Conditions (such as BS 6364)
   • When valves are used in low temperature environments (such as in the transportation of liquefied natural gas), relevant low temperature design standards need to be followed. The BS 6364 standard has detailed regulations on the material toughness, structural design, and measures to prevent brittle fracture of low temperature valves. For example, at low temperatures, the toughness of materials will decline and they are prone to brittle cracking. This standard requires that valve materials undergo low temperature impact tests to ensure that they can still work normally without cracking in low temperature environments.
   • There are also special requirements for seat and sealing materials to ensure good sealing performance under the combined action of low temperature and medium pressure. For instance, sealing materials with good low temperature elasticity are used to prevent the loss of sealing effect due to material hardening.