Water syphons
Water syphons protect the pressure gauges so that, for example, hot steam from the steam line cannot directly enter the pressure gauge but the pressure is transmitted by the intermediation of the liquid present in the water syphon.
Two basic models
The most common water syphon model is a steel or an acid-proof ‘pigtail’ where the pipe makes a full 360° loop while the water cushion remains inside the water seal. The other model is a water syphon with a 90° angle.