The primary function of a pigtail is to serve as a pressure buffer between the process and the instrument. When installed correctly, it allows condensate to collect in the coil, creating a protective fluid barrier. A pigtail is a coiled or looped section of tubing used in piping and instrumentation systems to absorb vibration, manage thermal expansion, and protect pressure instruments from direct exposure to process media. Moreover, its curved design allows it to flex under temperature or pressure changes. The most basic definition is that pigtail siphons are a type of siphon that is nothing more than a looped pipe, in this case in a spiral similar to a pigtail, hence its name, although sometimes it is also used the name lyre type siphon or just lyre. While it may seem like a minor detail, this bend serves several critical engineering purposes that protect the gauge and improve. A pigtail siphon protects pressure gauges from high-temperature steam by creating a condensed water barrier.
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