Fixed Speed with Two-Stage Airends and TEFC Induction Motor Ingersoll Rand R-Series fixed speed two stage compressors are the most reliable and energy-efficient solution for processes with constant demand. The compressors can be outfitted for continuous, trouble-free operation, and low energy consumption in the harshest conditions, even outdoors in rain and dust, from -10°F (-23°C) up to 131°F (55°C).