(1) Soft sealing material A. Nitrile rubber (NBR). Nitrile rubber has excellent oil resistance; heat resistance is superior to natural rubber and styrene-butadiene rubber; air tightness and water resistance are better. Nitrile rubber can be divided into butyronitrile-18, butyronitrile-26 and butyronitrile-40. Nitrile rubber is suitable for petroleum products with a temperature of -60 ° C ~ +120 ° ...