An air trap is a filtering device intended to remove contaminants from a compressed air supply. The main function of an air trap is the removal of moisture and oil from compressed air, both of which are undesirable compression cycle byproducts. Atmospheric contaminants such as soot, dust, paint, and solvent residue are also removed from the air supply in the same operation. The most common of these applications are the air traps on air compressors and air conditioners. Air traps are generally glass enclosed filter elements which are specifically rated for their intended application.
Air traps typically consist of a filter element enclosed in a transparent glass bowl. The glass enclosure allows a visual check to be made of the condition of the filter and how much water it has inside. Many air traps are fitted with a tap on the bottom of the bowl to allow for water to be periodically drained off from the filter enclosure. The cap of the filter has two fittings which allow the incoming and outgoing air hoses to be attached to the filter assembly. These filters are usually mounted between the compressor head and the storage tank or outgoing air hose.
The use of an air trap is necessary as air is heated when compressed; once it cools, moisture in the air condenses and forms water droplets which may contaminated the air supply or corrode the air storage tank. Oil vapor also enters the air supply from the compressor crankcase ventilation process and further contaminates the air supply. The air trap removes both the oil and water in addition to atmospheric pollutants which are drawn into the system. The use of air trap filters is not limited to air compressors though, and most air conditioning units also utilize them to remove condensation and compressor oil from the refrigerant gas.
There are several different types of air trap available for use on air compressors; it is important when installing one to ensure that it is correctly rated for the relevant application. Air traps cause a slight drop in the supply pressure of the compressor, and if incorrectly rated can have a negative effect on the compressors efficiency. Typically the air trap should not cause a drop in pressure of more than approximately five pounds per square inch (PSI). The internal filter element type should also be matched to the specific compressors intended use to ensure optimum filter protection and compressor efficiency.