What must protect the bourdon tube of a steam pressure gauge?

The bourdon tube of a steam pressure gauge must be protected by a loop seal, siphon, or pigtail to ensure accurate readings and to prevent damage from the high temperature of the steam. The primary function of these protective devices is to create a barrier between the hot steam and the sensitive material of the bourdon tube, which can be adversely affected by extreme heat.

When steam enters the gauge, it can cause rapid temperature increases, potentially leading to equipment failure or inaccurate pressure readings. The loop, siphon, or pigtail creates a hydraulic seal that traps a small amount of water, which absorbs much of the heat from the steam before it reaches the bourdon tube. This helps maintain the integrity of the measuring component and extends the functionality and reliability of the pressure gauge in high-temperature environments.

Other choices, such as a pressure relief valve, heat shield, or insulation tape, do not provide the appropriate direct protection needed for the bourdon tube against the specific hazards posed by steam. While they may serve other purposes in various systems, they do not fulfill the same protective role as a siphon, loop seal, or pigtail in the context of steam pressure measurement.