pfa of pfa ball valve is very similar in composition to the fluoropolymers ptfe and fep (fluorinated ethylene-propylene). pfa and fep both share ptfe's useful properties of low coefficient of friction and non-reactivity, but are more easily formable. fep is softer than ptfe and melts at 260 °c; it is highly transparent and resistant to sunlight.
提升卡
置顶卡
沉默卡
喧嚣卡
变色卡
千斤顶
显身卡