Provision is made for removing gaseous impurities, such as air, from hydraulic fluid in a hydraulic power system. A sump tank serves as a reservoir for the hydraulic fluid which passes through the power unit in a closed loop manner. The fluid inlet and outlet lines are connected to the tank below the...http://www.google.com.au/patents/US4385909?utm_source=gb-gplus-sharePatent US4385909 - De-aerator for hydraulic power units
