What is the purpose of the siphon between the boiler and the steam pressure gauge?

The purpose of the siphon between the boiler and the steam pressure gauge is primarily to prevent steam from entering the pressure gauge. This is accomplished by creating a barrier that keeps the high-temperature steam away from the gauge's internal mechanisms, which can be sensitive to heat.

By using a siphon, the steam cools as it travels through the pipe, which reduces the likelihood of damage or distortion within the gauge itself. This cooling effect allows the gauge to measure pressure more accurately and enhances the longevity of the instrument by protecting it from the damaging effects of direct steam exposure.

The other options, while they may sound relevant, do not capture the primary function of the siphon. For instance, while the siphon may incidentally help reduce pressure fluctuations or increase gauge lifespan by protecting it, its fundamental design is aimed more specifically at preventing steam ingress. Similarly, the siphon is not primarily designed for drainage or enhancing gauge accuracy, as its main job is to act as a coolant barrier for the gauge.