Screw compressors operate more or less like pumps, and have continuous flow refrigerant compared to reciprocals. Reciprocal have pulsations. This results in smooth compression with little vibration. Reciprocals, on the other hand, make pulsating sounds and vibrate. They can be very noisy.
Screw compressors have almost linear capacity-control mechanisms. That results in excellent part-load performance. Due to its smooth operation, low vibration screw compressors tend to have longer life than reciprocals.
Centrifugals are constant speed machines. These machines surge under certain operating conditions. This results in poor performance and high power consumption at part load. Screw compressors have proven themselves in tough refrigeration applications including on-board ships. Today, screw compressors practically dominate refrigerated ships, transporting fruits, vegetables, meats, and frozen foods across the ocean with good reliability. These compressors have replaced the traditional shipboard centrifugal.
Screw compressors were developed in Germany in the 1800s. They were patented in 1883 in Italy, but not in the United States until 1905. This type of compressor is a positive-displacement compressor. That means it uses a rotor driving another rotor (twin) or gate rotors (single) to provide the compression cycle. Both methods use injected fluids to cool the compressed gas, seal the rotor or rotors, and lubricate the bearings.