What is the purpose of a siphon or pigtail on a steam boiler?

The purpose of a siphon or pigtail on a steam boiler is to protect the steam gauge. It acts as a barrier between the high-temperature steam in the boiler and the steam gauge, helping to prevent direct exposure to the steam. This is crucial because direct exposure can cause damage to the gauge due to the extreme temperature and pressure conditions, leading to inaccurate readings or complete failure of the gauge.

The design of the siphon or pigtail allows it to trap a small amount of water, which acts as a cushion to absorb the heat. This water cools the steam before it reaches the gauge, ensuring that the gauge can accurately measure the steam pressure without being affected by the high temperature.

The other options focus on functions that do not pertain to the primary role of a siphon or pigtail. For instance, increasing boiler pressure, enhancing heat transfer, and regulating water levels are not functions performed by these components, as the siphon is specifically designed to protect measurement instruments rather than alter operational conditions of the boiler itself.