High service intervals in combination with outstanding fuel cleanliness are the current demands for fuel filter systems, reports Mann+Hummel, and an alignment of different filter stages is an alternative to one single, high efficiency filter cartridge. By balancing the size and increasing the efficiency at each stage, ultra-high filtration efficiencies can be realized in a compact design.
The efficiency and dust holding capacity of fuel filters are characterized by test standards such as ISO 4020-6.4 and ISO 19438. Usually pre- and main filters are characterized separately and designed based on test results for each stage. Up to now there is no established test method and test bench for multi-stage filter testing.
Mann+Hummel has developed a new test rig to enable the testing of up to four stages in line with using different test dusts such as the ISO 12103‑A3, ISO 12103‑A2, ISO 12103‑M2, ISO 12103‑M2 with soot and JIS Z8901 Class 11. Different test liquids can also be used.
In contrast to most of the standard test methods this bench test is designed to use more field relevant low viscous test fluids and variable test contaminants. In addition, up to four different flat sheet samples connected in series can be tested simultaneously. For each stage the differential pressure increase during particle loading can be determined. This enables an ideal design of different filter media layers and/or pre- and main filter combinations can be implemented to reach the optimum dust holding capacity. The filtration area of each flat sheet can be varied independently and allows a further degree of freedom in filter design and development.