The overall balance design of TW body and air barrel reduces the operation noise and vibration, and increases the service life of moving parts through low-speed rotation. In order to improve the sealing performance and reliability, high-strength grease lubricated bearings are used. In addition, crankcase cooling holes are added to prolong the service life of the bearing. The two-stage compression design of models above 5HP reduces the exhaust temperature and improves the efficiency. The suction and exhaust valve adopts a special high-temperature resistant disc valve design to improve the air tightness, and the stainless steel material is used to improve the quality and reliability. The compression ring used by the piston is a spring compression ring, which improves the air tightness during compression, reduces air leakage and greatly improves the volumetric efficiency.