By Josh Cosford, Contributing Editor
Desiccant, membrane, deliquescent, centrifugal and refrigerated air dryers are all technologies used to dry our compressed air systems. They are installed in various locations throughout the plant, although downstream of the compressor is the most critical location. Compressing air collects the volume of moisture found in a cubic foot of air and reduces it to a space only about an eighth the size, and the subsequent cooling results in a flood of condensation that must be dealt with.
The management of moisture is part and parcel to the operation of compressed air systems and is just as fundamental as emissions control on vehicles and sludge from wastewater treatment. With such an inherent source of contamination potentially affecting every air component in your plant or on your machine, how does the moisture affect pneumatic systems?
The obvious answer to how moisture affects air systems to anyone who works around pneumatics is, “very little.” The very nature of pneumatic systems requires that the constituents of any system are naturally resistant to moisture or the expulsion of it. Yes, excessive moisture accelerates wear by displacing oil, and any wet environment is more likely to encourage oxidation, especially in the presence of heat.
Although iron or steel valve bodies are no longer used in pneumatics (or at least rarely), steel cylinders are, especially in the mill-type and NFPA constructions, and we know that steel just straight-up rusts. Plus, even modern plants may still use cast-iron pipes for airline distribution, and it takes only a simple twist of the water-drain ball valve to see the rust-tainted condensation spatter your floor.
Still, with enough water, especially in a continuous state of contamination, moisture does affect performance. Even aluminum can oxidize over time, and some pneumatic seals are compatible with water. Equipment, such as air ratchets, air motors, and many cylinders, requires constant lubrication to prevent excessive wear, which is reduced or eliminated when water displaces it. And water can affect the performance of pilot-operated functions that rely on tiny holes remaining clear to transmit a pressure signal.
Of course, water in mobile systems is a different story, especially in cold climates. I don’t need to tell you that water freezes, and it can affect the performance of air cylinders on salter trucks, pneumatic tire inflation systems, and air brake systems. Freezing airlines or valves are an annoyance at best, but dangerous at the worst. This is why the components that constitute a pneumatic system must be able to handle not only moisture but also ice formation.
Expect construction materials to be moisture-resistant and to resist oxidation and corrosion, especially from within. Plastic, anodized aluminum, stainless steel, and even ceramic are all empowered to defend against the forces of evil and also allow pneumatics to maintain its respectable price point.
Manufacturers pay attention to small details to ensure reliability despite possible circulating or stagnating water. Galvanic corrosion occurs between two dissimilar metals, such as steel and aluminum, so any such combination is avoided by using similar metals. Should such unmatched pieces interface, designers will use rubber or plastic gaskets to prevent electron exchange. Of course, entirely different, non-conductive materials make great bedfellows, which is why ceramic spools are commonly used.
Moisture is ubiquitous in pneumatic systems, and because no drying system is perfectly efficient, cylinders, motors, and valves are designed to withstand even moderate amounts of water. Let’s be clear: you should avoid excessive moisture by using appropriate drying equipment, as water can degrade performance. But rest assured that even the most budget-friendly air components are resilient in the face of moisture.
