A filter device separating impurities from a gas, including a filter housing having a lid and a pot; the lid having an inlet and an outlet; a filter element in the pot with a top cap and a bottom cap with a filter cartridge therebetween; the top cap has an inlet duct connected to the lid inlet so that the gas to be purified is passed through the inlet duct to the filter cartridge; a space is between the lid and the top cap which is connected to the outlet of the lid; a switching element to be installed rotatably in the lid and rotatable between an off-position in which the inlet port or the outlet port connects to respectively the inlet or outlet of the lid, and a twisted position, in which the entrance of the inlet duct of the top cap can connect to the lid inlet.