PERMCO BACK UP RING

In a Permco hydraulic gear pump or motor, the back up ring sits with an O-ring and helps keep that primary seal from extruding when pressure spikes. It is there to support the seal so it holds its shape and keeps sealing through tougher duty cycles.

Genuine Permco OEM is exactly what this is. It's sourced directly from Permco and made to original equipment tolerances, so it'll fit and function the same as what came out of the pump when it was new. For a rebuild, that matters a lot more than folks sometimes realize, especially when you're trying to get a good seal the first time around.