HWS Dynamical seals are manufactured, that medium can only come in contact with glass or PTFE.
They can be used under vacuum and little overpressure(* according to security rules), however a fine ground(or polished)shaft in glass, metal or other materials is necessary.
A speed of max. 800 rpm should be only be exceed for a short time.
HWS-Dynamic seal for stirrers, self-adjusting, Pat.pend.
A coil in special steel presses the PTFE lips permanently against the shaft and glassbody.