Final answer:
A siphon coil, also known as a pigtail, is used in a steam gauge line to protect the Bourdon tube from steam exposure. It acts as a barrier, preventing steam from directly contacting the tube and causing damage. The siphon coil also protects the piping and the draft gauge by cooling the steam before it reaches them.
Step-by-step explanation:
A siphon coil, also known as a pigtail, is employed in a steam gauge line to protect the Bourdon tube from the effects of steam. The Bourdon tube is the measuring element in a steam gauge, and it can be damaged by direct exposure to steam. The siphon coil acts as a barrier between the steam and the Bourdon tube, preventing steam from directly contacting the tube and causing damage.
The Bourdon tube is a curved tube that changes shape as pressure changes. It is connected to a pointer that indicates the pressure on a dial. When steam enters the siphon coil, it condenses into liquid and prevents the hot steam from reaching the Bourdon tube. This protects the Bourdon tube and ensures accurate pressure readings.
In addition to protecting the Bourdon tube, a siphon coil also protects the piping and the draft gauge. The siphon coil acts as a heat exchanger, cooling the steam before it reaches the piping and the draft gauge. This prevents damage to the piping and ensures accurate readings on the draft gauge.