Filters for Air, Gas, and Liquids Filtration is commonly the mechanical or physical operation used for the separation of solids from fluids. A particulate air filter is a device used to remove solid particulates such as dust, pollen, mold, and bacteria from the air. An exhaust gas filter is used for internal combustion engines. Liquid filtration is the removal of solids from liquids by allowing the flow of the contaminated liquid through a filter medium that will retain the solid particulates and allow only clean liquid to pass through. At Engineered Pressure Vessels we provide only the highest quality filtration systems for our customers.