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leaving a compressor is hot, dirty and wet, which can be damaging to—and also shorten the lives of— downstream components, such as valves and cylinders. Before air can be reliably used, it needs to be filtered, regulated and sometimes lubricated. An air line filter traps particle and liquid contamination in compressed air. It strains the air to trap solid particles (dust, dirt, rust), and also separates liquids (like water and oil) entrained in the compressed air. Filters are installed in the line upstream of regulators, lubricators, directional control valves and airdriven devices such as cylinders and motors. Filters remove impurities from the pneumatic system, preventing damage to equipment and reducing production losses due to contaminant-related downtime. Downtime in an industrial plant is expensive and is often the result of a contaminated and poorly maintained compressed air system. The size of an air filter is selected based on the maximum airflow through the unit, and care should be taken in referencing the manufacturer’s flow characteristics chart. Just like any pneumatic component, inlet and outlet pressure factor into air flow, but you should also consider the pressure drop characteristics of the filter itself, which can be high if the unit is undersized, causing a reduction in flow.
FLUID POWER WORLD
6 • 2016
There are three types of filters: general purpose, coalescing and vapor removal. General purpose filters are used to remove water and particles, coalescing to remove oil, and vapor removal to evacuate oil vapor and odor. Pressure regulators reduce and control fluid pressure in compressed air systems. Regulators are also frequently referred to as PRVs (pressure reducing valves). Optimally, a regulator maintains a constant output pressure regardless of variations in the input pressure and downstream flow requirements, so long as upstream pressure doesn’t drop below that of downstream. In practice, output pressure is influenced to some degree by variations in primary pressure and flow. Pressure regulators are used to control pressure to air tools, impact wrenches, blow guns, air gauging equipment, air cylinders, air bearings, air motors, spraying devices, fluidic systems, air logic valves, aerosol lubrication systems and most other fluid power applications requiring subordinated pressure. Regulators employ a control-spring acting upon a diaphragm to regulate pressure, and its spring rate determines the range of pressure adjustment. General purpose regulators are available in relieving or nonrelieving types. Relieving regulators can be adjusted over a wide pressure range, and even when downstream flow is blocked at the reducing valve, relieving regulators will
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Fluid Power World Handbook 2016