Pressure gauge siphons are used to protect the pressure gauge from the effect of hot pressure media such as steam and also to reduce the effect of rapid pressure surges. The pressure medium forms a condensate and is collected inside the coil or pigtail portion of the siphon. The condensate prevents the hot media from coming in direct contact with the pressure instrument. When the siphon is first installed, it should be filled with water or any other suitable separating liquid.
It can also be used to reduce the potentially damaging effects of rapid pressure changes. These low-cost devices allow systems builders to use a pressure sensor with a much lower temperature range in high-temperature applications.
Forms
Pigtail syphon
Coil syphon
Pressure Gauge Siphon Heat Dissipation Chart
Different types of Pressure gauge siphons available in the market. As per our operating temperature, the Siphon’s shape, size, material, and other factors will change. Instrumentation vendors suggests the suitable siphon.

From the below example chart, the pressure gauge siphon acts as a thermal barrier between the process media and pressure gauge.
Note: The chart specifications will change based on the type of pressure gauge siphon. The below chart displays the readings for 3 different siphons.
These graphs represents the heat dissipation based on results of a specific laboratory test. These results may vary in the field based on multiple factors such as ambient temperature, type of process media and/or velocity. This data set is to be used as a reference point only. These test results are based on an ambient temperature of 68°F.
References: wika, Ashcroft