PTFE bellow mechanical seals are desinged to endure extremely corrosive mechanicals including as concentrated acids and salts,strong oxidizing and reducing agents,and chemically active organic compounds. Mechanical seals often need to be used in chemicals because mechanical seals with elastomers made of FKM, Kalrez or Chemrez can't hold up extreme corrosion and PTFE/Teflon can work properly in extremely corrosive chemicals.