A housing module of a fluid treatment module of a fluid system is provided with a fluid housing with inlet and outlet for fluid. The fluid housing has a housing part with a receiving chamber for a fluid treatment component for treatment of fluid and an installation opening, closable by a housing closure part, for installation of the fluid treatment component in the receiving chamber. A housing connecting section is provided for connecting the housing part and the housing closure part to each other. The housing module has an externally positioned support structure that surrounds the housing part like a sleeve and has a reinforcement region that extends about the housing connecting section. The support structure has a fastening region for attachment of the housing module on a holding component of the fluid system. The connection of the housing part with the housing closure part is a direct connection.

A method for filtering a fluid that includes collecting contaminates in the fluid, passing the fluid from inside an internal cavity of a first shaft through a tight clearance at a spline connection between the first shaft and a second shaft such that the fluid is filtered of contaminates as a result of the tight clearance, and delivering the filtered fluid to a delivery location.

A method for filtering a fluid that includes collecting contaminates in the fluid, passing the fluid from inside an internal cavity of a first shaft through a tight clearance at a spline connection between the first shaft and a second shaft such that the fluid is filtered of contaminates as a result of the tight clearance, and delivering the filtered fluid to a delivery location.

An assembly for filtering a fluid includes a first rotatable shaft with a first set of splines. The first rotatable shaft has an internal cavity containing the fluid. Also included is a second rotatable shaft with a second set of splines mated to the first set of splines. The second rotatable shaft includes at least a portion of a supply hole. The first rotatable shaft and the second rotatable shaft are configured to convey the fluid from the internal cavity through a tight clearance between the first set of splines and the second set of splines, to filter the fluid, and then out the supply hole.

A lubricating oil purification system for purifying a stock solution mixed with ammonia water into lubricating oil, the lubricating oil purification system includes: an engine; a lubricating oil purifier configured to separate a stock solution containing the lubricating oil used in the engine into a light liquid which is at least the purified lubricating oil and a heavy liquid containing ammonia; and a water supply unit configured to supply water into a separation chamber during operation of the lubricating oil purifier.