Air filters are the only one of the four types with no bypass valve,
and that is deliberate: it is better for an engine to be starved of air than fed
unfiltered air. So a blocked air filter announces itself through lost power and black
smoke rather than quietly going out of circuit.
Two seal types appear below and they are not interchangeable even where the
dimensions look close. An axial seal clamps flat between the housing
and the cover. A radial seal seals on its inside diameter against the
housing neck. Check which one your cleaner takes.
Where a housing holds a second, inner element, that safety filter has its own number
and its own interval — the AF424 pairs with the AF820M, for instance. More in
choosing the correct air filter and
air filter troubleshooting.
The Perkins numbers are listed differently from the rest, and
deliberately. Perkins publish fitment by engine rather than by dimension,
so each card leads with the engine series and the exact models the part is fitted
to. That is how a Perkins buyer identifies a filter anyway: from the engine plate,
not from a tape measure. If you have the engine number, send it and we will match
the part to it.
The three Perkins elements below cover most of the range between them: 26510337 for
the 100 and 400 Series and smaller 1100 engines, 26510342 for the 1104 and 4.236,
and 26510353 for the six-cylinder 1006, 1106 and 1206. They are primary elements,
so check whether your housing also takes a safety element behind it.