higher air cleaning power than air cleaner of known type even though the outer dimensions of the casing 50 differ little from these this is because in addition to the known filter cartridges 62 and 118 of metal mesh it also comprises the paper filter cartridge 35 of relatively small height but of relatively high filtering power as the filter cartridge 35 is in the form of a plurality of adjacent portions 47 folded in radial directions and of relatively small height it has a very high filter area for a minimum external bulk and has good operational reliability the described air cleaner also has further characteristics which increase its air cleaning power so enabling it to be used advantageously in particularly severe conditions in this respect a suction action is generated on the oil in the minimum section region at the slots 81 leading to a more intimate mixing with the air and in addition the fins 110 on the member 108 provide a centrifugal action on the air and on the oil and impurity particles so aiding their separation the described air cleaner also has good cleaning power at low throughputs this is because at low throughputs the oil level in the bottom 53 is relatively high so that the uncovered section of the spaces 94 in the toothing 92 is relatively small there is thus a flow velocity of the air through the spaces 94 which is sufficient to allow it to associate itself with the necessary oil quantity for cleaning the air this flow velocity.