How to Minimize Water Vapor in Instrument Air/Pneumatic Systems

Water is one of the most common contaminants in instrument air systems, causing corrosion of metal components and as a result clogging of orifices. Special devices referred to as air dryers installed in instrument air systems use solid materials called desiccants to absorb water entrained in the compressed air. The desiccant material is “regenerated” by the dryer mechanism on a regular cycle; however it must be periodically replaced when its water-absorbing ability diminishes.

A simple technique to help extract water from an instrument air system is an accessory termed to as a water trap, typically found on air pressure regulators, this usually comes in form of a drain valve at the bottom of the regulator which should be opened periodically by maintenance personnel to allow for the collected water to be blown out of the regulator.

Another method to help minimize the amount of water reaching pneumatic devices is to properly orient all connections to the main air pipe (called header). Ideally, each instrument air tap coming off a header should do so on the top of the header, not the bottom. This way, the collected condensation inside the header will not go directly to the points of use, but rather will drain downhill to the lowest point in the header where a drain valve may be positioned. This is illustrated in the figure below:

In order to facilitate draining the header, the header should be slightly inclined, with the drain valve installed at the lowest point. Another key point to note, copper, brass, plastic and stainless steel are the preferred materials for instrument air piping, tubing, valves and fittings, since standard (iron) pipe will inexorably rust in the presence of condensation. Particles of rust created inside an instrument air system can cause a big problem with the tiny ports, nozzles, and orifices of pneumatic instruments.

Also read: Pneumatic Actuators

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