The rotor seal is the polymeric disc that makes a high pressure seal against the stator. The seal wears with use and is one of the only parts that may need routine replacement. Stators need replacement 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 and sulfuric are not compatible with PEEK. Don't Risk using imitation parts. Only Genuine PerkinElmer authorized Rheodyne rotor seals confidently maintain Rheodyne Valve performance in your validated instruments.