The seat material shall be one of the following materials : ethylene - propylene - diene monomer ( epdm ) or fluoroelastomer ( fpm ) with polytetrafluoroethylene ( ptfe ) bearing support at the top and bottom 阀座材料应该是下列材料之一：乙烯-丙烯-二烯系单体(三元乙丙橡胶)或氟橡胶( fpm ) ，在顶部和底部配置聚四氟乙烯( ptfe )轴承支撑。
