短语词组短語liquid piston fibrous packing ring 液缸活塞纖維填料環equalizing piston packing ring 平衡活塞密封圈piston ring packing detail 活塞環密封piston ring packing 活塞環密封split -ring piston packing [機]開環式活塞脹圈 返回 piston packing ring