Why is a pigtail used when connecting a Bourdon tube steam gauge to a boiler?

A pigtail is used when connecting a Bourdon tube steam gauge to a boiler primarily to protect the Bourdon tube from direct exposure to steam. This is crucial because direct contact with high-temperature steam can cause the Bourdon tube to experience thermal stress, potentially leading to inaccurate readings or even damage to the gauge. The pigtail design acts as a buffer, allowing steam to cool before it reaches the gauge, thus ensuring the instrument operates within safe temperature limits.

In addition to protection from steam, the pigtail can help prevent the accumulation of condensate within the gauge, which could further compromise its function and accuracy. The design enhances the durability of the gauge in high-pressure steam systems, extending its lifespan and maintaining the reliability of the readings it provides.

This aspect of gauge installation is fundamental to ensuring accurate monitoring and operational safety in a system where pressure and temperature management are critical.