ISO 19438:2003 specifies a multi-pass filtration test, with continuous contaminant injection and using the on-line particle counting method, for evaluating the performance of fuel filters for internal combustion engines submitted to a constant flow rate of test liquid. The test procedure determines the contaminant capacity of a filter, its particulate removal characteristics and differential pressure. ISO 19438:2003 is applicable to filter elements having a rated flow of between 50 l/h and 800 l/h; however, by agreement between filter manufacturer and customer, and with some modification, the procedure is permitted for application to fuel filters with higher flow rates.