Combination of off-line filter unit and plate heat exchanger with low water consumption or air blast coolers. A selection of high quality filter elements for specified system cleanliness. The reliability and working life of hydraulic, lubricant or coolant oil and components depends on the cleanliness of the fluid and the regulation of the operating temperature. Independent of pressure ripples and flow surges, off-line filters develop potentially the best possible particulate retention. When combined with other system components such as coolers, installation cost and space can be minimised.