The seal, which is manufactured in Hythane® 181, is designed to provide a valve action to prevent excessive pressure build up in the cavity between the buffer seal and the rod seal. A polyacetal anti-extrusion ring is fitted to provide maximum extrusion resistance against shock pressure loads.
The Hallite 653 is a patented product:
European patent no. 0427554BI.
U.S.A. patent no. 5088747.