Parker Back Up Ring Seal 180004N0300 prevents migration of O-rings into the sealing gap when subjected to high pressures.

Parker Parbak Back Up Ring is a Parker Parbak standard rubber back-up ring of contoured design. It is intended for use in dynamic and static seal applications.
Features of Parker Parbak Back Up Ring:
Elastic memory permits Parker Parbak Back Up Ring to be stretched into place for assembly without preconditioning or cutting.
Continuous construction prevents damage to the o-ring seal.
Lubrication is enhanced by rubber which absorbs system fluid and does not plate out on rubbing surfaces.
We have in total 4 kinds of brands back up ring with a total number of 440 types of back up rings.
1, Parker back up ring 
2, HITACHI  back up ring 
3,Sidahang  back up ring 
4,Hallite  back up ring