The rotor seal is the polymeric disc that makes a high pressureseal against the stator. The seal wears with use and is one of theonly parts that may need routine replacement. Stators needreplacement only if the ports become damaged. Vespel blend rotor seals have an operating pH range from 0 to10. Tefzel blend and PEEK blend rotor seals have a pH range from 0to 14. Strong oxidizing acids such as concentrated nitric andsulfuric are not compatible with PEEK. Don't risk using imitation parts. Only Genuine PerkinElmer authorized Rheodyne rotor seals confidently maintain Rheodyne Valveperformance in your validated instruments.