NPXX 非平衡式單彈簧驅動機械軸封,彈簧迫緊於軸心跟隨轉動,依型式區分:
NP1X:碳精+金屬
NP2X:單體碳精/碳化矽/碳化鎢
NP3X:碳化矽/碳化鎢+金屬
搭配"A2","A3","A4","A6","A9"固定環