In a GPS two-stage series screw compressor, the high temperature air produced after the first stage of compression is first cooled down by oil while remaining at constant pressure before reaching the second stage of compression. The entire compression process is close to isothermal compression, which reduces potential energy loss. The pressure ratio for each stage of two-stage compression is decreased and leakage at the rotor seals is reduced significantly. In comparison with single-stage compression, the theoretical air delivery volume can be increased by up to 8 – 15% and the energy consumption can be reduced by 8 – 15% correspondingly. The price–performance ratio is best when running at full load for long periods of time. With two-stage compression, parts are enduring less stress at each stage and the thermal load is lower, therefore allowing for a longer service life.