Some models of Caleffi's automatic air vents are equipped with a hygroscopic safety vent cap including the 5020 Series MINICAL and 5022 Series VALCAL. It's referred to as a safety cap because it will seal off the vent if water gets into the cap area. This feature protects against potential vent spit and is perfect for locations that are not easily accessible and for locations where dripping water is absolutely unacceptable.
Here's how they work: inside the cap are a number of very thin, washer-shaped discs made of a cellulose fiber - a natural plant-based material that expands by 50% immediately when wet. This expansion seals the vent opening. Once the discs dry out, they shrink down again to allow air passage.
The hygroscopic cap MUST BE HAND TIGHTENED in order to work properly; do not leave it partially unscrewed as is done with a standard vent cap. Standard caps must be left partially unscrewed to vent air and they provide an air-tight seal when tightened. The hygroscopic cap is different; it is not designed to provide an air-tight seal and if left partially unscrewed it will leak water!
Caleffi utilizes the same hygroscopic technology in the 5080 Series manual vent which is perfect for radiators and high points in piping systems. Hand-tighten the 5080 for automatic air release operation or open it to fast-release air (or water) for example when filling/purging the hydronic system.
The hygroscopic products from Caleffi are a great problem-solver and are extremely popular! Check them out and, as always, let us know if you have any questions!