API 594 intermational standard covers design,material, face-to-face dimensions,pressure-temperature ratings,and examination, inspection, and test requirements for two types of check valves.
Type 'A' check valves are short face-to-face as defined in Table 3 and Table 4 and can be: wafer, lug, or double flanged; single plate or dual plate; gray iron, ductile iron, steel, nickel alloy, or other alloy designed for installation between Classes 125 and 250 cast iron flanges as specified in ASME B16.1, between Classes 150 and 300 ductile iron flanges as specified in ASME B16.42, between Classes 150 and 2500 steel flanges as specified in ASME B16.5, and between Classes 150 and 600 steel pipeline flanges as specified in MSS SP-44 or steel flanges as specified in ASME B16.47.
Type 'B' bolted cover swing check valves are long face-to-face as defined in 5.1.2 and can be:flanged or butt-
welding ends of steel, nickel alloy, or other alloy material. End flanges shall be as specified in ASME B16.5 or
ends shall be butt-welding as specified in ASME B16.25.
Structural Length and Design
Type A:
Short Structure: Shorter valve body length, compact structure, suitable for piping systems with limited installation space.
End Connection: Typically uses wafer, lug, or double flange connections.
Type B:
Long Structure: Longer valve body length, providing a larger flow area and better sealing performance.
End Connection: Typically uses flanged or weld neck connections, suitable for high-pressure or high-temperature piping systems.
Materials and Applicability
Type A:
Materials: Commonly used gray cast iron, ductile iron, or materials conforming to ASME B16.34.
Applicable Scenarios: Suitable for industrial pipelines such as oil and gas, especially suitable for space-constrained installation environments.
Type B:
Materials: Must use materials conforming to ASME B16.34, such as stainless steel or alloy steel.
Applicable Scenarios: Suitable for high-pressure, high-temperature, or piping systems requiring higher sealing performance.
Testing and Certification
Type A:
Testing Requirements: Must pass tests according to standards such as API 598 and ASME B16.10 to ensure sealing and strength.
Type B:
Testing Requirements: Also requires passing tests according to standards such as API 598 and ASME B16.10, but may involve more stringent pressure testing.
Application Scenarios
Type A:
Typical Applications: Piping systems with limited space, such as urban water supply and industrial pipe networks.
Type B:
Typical Applications: Piping systems in the oil, natural gas, and chemical industries that require high pressure, high temperature, or higher sealing performance.
Selection Recommendations
Choose Type A: If pipeline space is limited and the medium pressure and temperature are moderate, Type A is a more economical choice.
Choose Type B: If the pipeline system has high pressure and high temperature, or requires higher sealing performance, Type B is more reliable.
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