DELTA 50-875 3-Speed Air Filtration System with Remote Highest airflow 3-speed air cleaner in its class Filters shop air faster than competition Remote control allows you to select from three speeds and set your time delay shut-off up to four hours Patent-pending dirty filter indicator determines the efficiency of your filter. When the needle points to the red it is time to clean your filter. Filters trap particles larger than 1 micron; Electrostatic filter is standard