Abstract: This invention relates to water-based hydrophilic coatings suitable for giving hydrophilicity primarily to the surface of aluminum and to a process for manufacturing precoated fin materials for heat exchangers with use of said coatings. The coatings are composed of colloidal silica with a dispersed particle diameter of 5 to 100 nm, water-soluble polymers containing at least carboxylic acid polymers, anionic surfactants and water; the colloidal silica and the water-soluble polymers are present at a weight ratio of 30:70 to 70:30 on a solid basis in a combined content of 4 to 20% by weight, the content of carboxyl group in the carboxylic acid polymers contained in the water-soluble polymers is 20 to 63% by weight, the anionic surfactants are alkali salts of sulfosuccinic acid monoalkyl esters with alkyl groups containing 1 to 18 carbon atoms and present in an amount of 5 to 20% by weight of the combined solid content of the colloidal silica and the water-soluble polymers, and the pH is 1 to 5 as a whole.

Abstract: This invention pertains to a filter in general and particularly to a filter for use in filtering hydraulic oil circulating in a hydraulic system provided for a hydraulic machine. The filter is formed in a loop and includes at least two filtering materials having different filtration porosities. Those filtering materials are arranged in the circumferential direction of the loop. Since filtering materials are arranged in the circumferential direction, the filter can be manufactured at the same size as the existing filters so that it can be accommodated in the existing filter cases. Also, since the filter has more than one filtration accuracies, it is capable of catching impurities of various sizes. In operation, most of the liquid to be filtered tends to pass through the less fine filtration martial. Thus, the filter creates a small pressure loss.

Abstract: A filter system for a liquid, which system has a base with an inlet for incoming unfiltered liquid and an outlet for outgoing filtered liquid and a filter subassembly having a filter unit and structure for removably maintaining the filter unit in an operative position on the base. There is a first lead-in port on the base in communication with the base inlet and a first lead-out port on the base in communication with the base outlet. There is a second lead-in port on the filter unit and a second lead-out port on the filter unit. The filter unit further has structure for filtering liquid communicating between the second lead-in port and the second lead-out port.