Soft sealing butterfly valve for 100 ℃ below the hot water, cold water system. If the system requires a higher temperature, available metal sealing butterfly valve (available in the system below 500 ℃). Soft sealing butterfly valve seals (all kinds of commonly used rubber, PTFE) the highest temperature: nitrile rubber NBR ≤ 80 ℃, EPDM EPDM ≤ 120 ℃, PTFE PTFE ≤ 150 ℃. In the acid-base medium, the maximum temperature is: 1, neoprene: nitric acid (10%) 29 ℃; citric acid 29 ℃; sodium hydroxide 93 ℃. 2, butyl rubber: sulfuric acid (50%) 66 ℃; nitric acid (10%) 40 ℃; sodium hydroxide 85 ℃. 3, F4: sulfuric acid (0-100%) 180 ° C; nitric acid (0-100%) 180 ° C; sodium hydroxide 180 ° C.