Air compressors are used to push air into the fuel cell stack. The fuel cell extracts oxygen from the incoming air to enable the reaction at the cathode. In fuel cell systems, the air compressor is also sometimes called an air blower. The performance of a fuel cell system depends significantly on the amount of air available. This makes the compressor one of the most critical components. When used in fuel cell systems it is often critical that the compressor does not introduce any impurities such as oil into the air flow, as this could be harmful to the fuel cells themselves. This is the case for instance in applications with proton exchange membrane fuel cells (PEMFC). There are several ways by which air compressors, or air blowers, can be categorized: e.g. in reciprocating air compressors, centrifugal compressors, and rotary screw compressors.