A booster compressor is a compressor that works with air that has been compressed and compresses it to a higher pressure. It is used to compensate the pressure drop in long pipelines or in applications where a higher pressure is required for a sub-process. Compression may be single or multi-staged and the compressor can be of a dynamic or displacement type, but piston compressors are the most common. The power requirement for a booster compressor increases with a rising pressure ratio, while the mass flow drops. The curve for power requirement as a function of the intake pressure has the same general form as the curve for a vacuum pump.