ISO 3668:2017规定了评估液压过滤器压差与流量特性的程序，并构成过滤器制造商和用户之间协议的基础。 它还规定了一种方法，用于测量在不同流速和粘度下由过滤器组件的相关零件、旋装式过滤器和过滤器内的任何阀门产生的压差，这些阀门位于气流中。待测试过滤器的典型类型如下: 类型1:为旋装式过滤器，其中可更换单元不包括过滤头（可能包括也可能不包括滤芯旁通阀）； 类型2:为旋装式过滤器，其中可更换滤芯与过滤头一起测试（可能包括滤芯，也可能不包括滤芯）- 旁通阀）； 类型3:为过滤器组件，通常为更换滤芯类型，即外壳（封头和滤杯）和滤芯。

ISO 3668:2017 specifies a procedure for evaluating differential pressure versus flow characteristics of hydraulic filters and constitutes a basis for agreement between the filter manufacturer and user. It also specifies a method for measurement of the differential pressure generated at different flow rates and viscosities by the relevant parts of a filter assembly, spin-on and any valves contained within the filter which are in the flow stream. The typical types of filter to be tested are as follows: Type 1: which are spin-on filters in which the replaceable unit does not include a filter head (it might or might not include the element by-pass valve); Type 2: which are spin-on filters in which the replaceable element is tested together with a filter head (it might or might not include the element by-pass valve); Type 3: which are filter assembly, usually of the replacement element type, that is the housing (head and bowl) and element.