Dual-seal valve
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What does dual sealing of a valve mean? Is it a soft seal plus a hard seal, or two seals of the same type? Also, do fire valves that meet API 607 requirements – those that can form a hard seal after the soft seal is burned out – qualify as double-sealed?
Double sealing can take the form of a combination of soft + hard seals, or soft + soft seals; a hard + hard combination is also possible. This depends on the specific technical requirements and structural design. Fire valves are generally not considered to have double sealing; in most cases, double sealing does function, with the aim of reducing internal leakage in the valve.
What is specified in API607 cannot be considered a double seal. Double sealing refers to a sealing arrangement that features two sealing surfaces, which can be soft-soft seals or soft-hard seals.
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