What is a Steam Pressure Gauge Siphon? Refineries, petrochemical plants and industrial factories utilize steam as a pressurized fuel for energy consumption. With steam also comes very high temperature and associated process pressure. When there is a need to measure steam process line pressure, the pressure gauge must be protected from these elevated temperature and pressure surges. Without protection, the gauge could be rendered damaged and inoperable. This is where a siphon comes in. Siphons protect gauges from elevated process temperature or, in this case, steam and damage when they are exposed to surges of steam. The two most common types of siphons are: • Pigtail siphons, which are meant for vertical piping configurations. • Coil siphons, which are meant for vertical or horizontal applications and have a slight dip in the loop design to provide for the trapped water in a horizontal position. Siphons are designed to be low-cost and are typically offered in carbon steel, stainless steel or brass. Siphon materials have corresponding temperature and pressure ratings. This is important when choosing the right siphon for your application. Siphons are rated with a maximum allowable working pressure (MAWP). This correlates to the material of the siphon and the wall thickness of the siphon. Choose carefully based on your process. Although the siphon may be compatible with your MAWP and corresponding steam temperature, also consider its dissipation capability. In other words, will the siphon dissipate enough process temperature to adequately protect the instrument? Pigtail and coil siphons are looped or coiled pipes that are placed directly on piping before a pressure gauge. Pressure gauges generally have a standard operating temperature rating of 200 °F (93 °C), possibly as high as 250 °F (121 °C), and even low-temperature steam services can reach a temperature that will damage a gauge.