Special elements are used sometimes in panel filters, which increase their rigidity during exploitation. These are specially made glue trickles, metal or plastic nets. They harden the filter, especially in large capacity engines or turbo engines where the requirement for air is relatively high. The filter cartridge in exposed then to major bending forces trying to suck it into the engine. It is quite a dangerous effect in the final stage of filter exploitation when contaminants clog the pores of the filter medium and cause major air flow resistance, increasing the pressure difference before and behind the filter. The characteristic symptoms in this case are significant engine power drops and increased fuel usage.Filter replacement should not be omitted considering not only the amount of kilometres but also exploitation conditions (high air dustiness).