Internormen Filters Private Ltd. Manufactures Vertical Return Line Suction Filter. Internormen Filters Private Ltd. Is an ISO 9001: 2000 certified company offering a wide range of filters for hydraulic and lubricating fluids and contamination monitoring system. The Vertical Return Line Suction Filter of model number RF 210-320 is designed for connection in return pipes and allows feed pressure at ,IN" connection to be pressurized to 10 bar. The Vertical Return Line Suction Filter can be used with mineral oils, bio-oils, emulsions and most synthetic hydraulic fluids and lubricating oils.