Vent dryers remove moisture from headspaces

As well as preventing water vapour adsorption occurring whenever vessel contents are exposed to ambient humidity during normal use, these rechargeable units also minimise pressure differential and odour emissions, give full weather protection, assist flame suppression and reduce the build-up of ignitable vapours.

An active desiccant bed retains any moisture before it can enter the vessel; Brownell says that field trials have proven that all existing condensation is quickly removed when these vent dryers are fitted to new vessels of polished fluid. A colour change visible from outside indicates when to change the beaded silica gel, and this is achieved by simply removing an access port plug.

If a fluid is contaminated by moisture adsorption, many of its active properties can be altered significantly. Opening an unprotected vessel immediately admits humidity, which can contaminate the fluid. Similarly, temperature changes in the fluid and headspace can lead to air being drawn in via the vent, which can lead to problems unless measures are taken to remove the moisture.