ISO 21018-3:2008规定了使用过滤器堵塞技术（也称为网格遮蔽法或孔隙堵塞技术）在线或离线测定容器中颗粒污染水平的半定量方法。ISO 21018-3:2008还规定了在实验室和使用中校准仪器和验证其正确运行的程序。 一般来说，这些技术适用于监测液压系统的一般清洁度水平、冲洗操作的进度、支持设备和试验台。 ISO 21018-3:2008适用于所有单相或多相液体系统。

ISO 21018-3:2008 specifies a method for the semi-quantitative determination of the particulate contamination level using the filter blockage technique (also known as the mesh-obscuration method or the pore-blockage technique) either on-line or off-line in containers. ISO 21018-3:2008 also defines procedures for calibrating the instruments and verifying their correct operation both in the laboratory and in service. In general, the techniques are suitable for monitoring the general cleanliness level in hydraulic systems, the progress in flushing operations and support equipment and test rigs. The use of ISO 21018-3:2008 is applicable to all single- or multi-phase liquid systems.