The ways filters are classified, from how they work and how they are rated to where they sit in a hydraulic system and how they are built.

A guide to the main filter media: cellulose, glass fibre, synthetic fibre, membranes, woven wire mesh, sintered metal and activated carbon.

How the ASTM D2276 field method and the D5452 laboratory method weigh the dirt in aviation fuel, and what that means for fuel filtration.

How the ASTM D3948 and D7224 MSEP tests rate jet fuel's ability to give up water, and why the rating matters for coalescers and filter separators.

How ASTM D7619 counts particles in diesel, jet fuel and biodiesel, and what the counts mean for fuel filtration.

Why particles matter in transformer oil, how ASTM D6786 counts them, and how the counts show whether oil filtration is working.

How ASTM D7647 counts particles in hydraulic and lubricating oils, why it dilutes the sample, and how the result guides the choice of filter element.

How ASTM F838 challenges a membrane filter with bacteria to show it is sterilising grade, and how that result links to the bubble point test.

How the ASTM F316 bubble point and mean flow pore tests measure the pore size of membrane filters, and what the results mean for a membrane cartridge.

Which ASTM standards apply to filters and filter elements, what each one measures, and which Vens filters meet them.

What each test in the Vens filter laboratory measures: multipass, integrity, particle counting, flow versus pressure drop, efficiency, and visual and dimensional checks.

FilterDex holds 65,223 filter element part numbers from 35 brands and finds an element by part number, by size or from a whole list. Here is what it does and how it compares.

FilterDex holds 507 element part numbers for Caterpillar, Komatsu, John Deere, WIX, MANN-FILTER, Bosch, Moog and UFI. Find yours and get the Vens Hydroluft equivalent.

FilterDex holds 208 Argo-Hytos element part numbers. Find yours, see its size and micron rating, and get the Vens Hydroluft equivalent.

FilterDex holds 233 PTI element part numbers. Find yours, see its size and micron rating, and get the Vens Hydroluft equivalent.

FilterDex holds 274 FBN element part numbers. Find yours, see its size and micron rating, and get the Vens Hydroluft equivalent.

FilterDex holds 365 Baldwin element part numbers. Find yours, see its size and micron rating, and get the Vens Hydroluft equivalent.

FilterDex holds 405 Fleetguard element part numbers. Find yours, see its size and micron rating, and get the Vens Hydroluft equivalent.

FilterDex holds 437 FBO element part numbers. Find yours, see its size and micron rating, and get the Vens Hydroluft equivalent.

FilterDex holds 444 HIFI Filter element part numbers. Find yours, see its size and micron rating, and get the Vens Hydroluft equivalent.