ISO 28520:2009 provides guidance for flushing of lubricating oil systems, and grading of the resultant cleanliness. The flushing process is twofold:to remove dirt from the erection and installation, andto demonstrate that the pipes and the system as a whole is sufficiently clean. Crankcase and, where applicable, gearbox etc. are cleaned separately before flushing, and requirements relating to this are also specified in ISO 28520:2009. Similar considerations apply to the system tank and other components of the system.For the purposes of ISO 28520:2009, the cleaning process is considered as “washing through” when the Reynolds is equal to or less than 3 000 and “flushing” when the Reynolds number is equal to or greater than 3 000.Where available, any original equipment manufacturer requirements for flushing take precedence over the requirements outlined in ISO 28520:2009.