Which of the following system applications would require the use of a siphon tube (pigtail) to prevent gauge damage?

Correct Answer: Option D — Steam pressure

Siphon tubes, or pigtails, are required for steam pressure gauges to prevent live steam from entering the gauge mechanism. The loop traps condensate, creating a cool water seal that protects the delicate Bourdon tube from the damaging effects of high-temperature steam, ensuring accurate readings and long-term gauge integrity.