While the Pomon wasn't a perfect filter (it only cleaned the air to 80% purity at 1 gram per cubic centimeter), the Soviets already had a better filter in 1940: the "Vortex", planned for installation on the T-50. The Vortex, developed at factory # 174, could filter the air to 98% purity without being cleaned for 10 hours. However, the T-50 fate was rather unfortunate, and it was not made in large numbers. The filter was then successfully used on KV tanks, until it was replaced by the Cyclone filter. It was also used on early KV-1S tanks, SU-152 SPGs, and the KV-13.
Figure 44: "Vortex" type air filter, used on KV tanks. CAMD RF 38-11355-2543
The air is cleared by entering the filter at an angle, and forming a vortex, dropping the dust into the oil pan underneath. The Cyclone filter, Vortex's replacement, reverses the flow of air, dropping the dust out of it more effectively, like so:
I have previously mentioned the Multicyclone filter. Let's take a closer look.
CAMD RF 38-11355-1630
Multicyclone filters installed in the KV-1S (top) and IS tanks (bottom)
Even the Cyclone filter, which provided 99.4% air purity at air dustiness of 1 gram per cubic meter, was unsatisfactory to the Soviets. In May of 1943, a new filter was tested on the KV-13 (Object 233), which provided 100% air purity at dustiness of 3 grams per cubic meter, and could operate without cleaning for twice as long as Cyclone.
The air filter was installed in all Soviet medium and heavy tanks from 1943 onward.