FRL units are parts installed to prevent problems in air-pressure lines. The name FRL unit comes from the 3 items usually used in the set—an air filter (F), regulator (R) and lubricator (L). FRL units function primarily by stably operating equipment and parts incorporated into air-pressure lines. Specifically, they remove dust, tar, impurities and condensate (condensation) that are generated in the line or enter it. They also supply and maintain pressure, supply lubricating oil and perform other functions. Some FRL units use combinations of a separate filter, regulator and lubricator. There are also combination-type products in which 2 or all 3 of the 3 items are preconnected.