What is used to prevent extrusion of an O-ring seal in a high-pressure system?

In high-pressure systems, preventing the extrusion of an O-ring seal is crucial for maintaining integrity and performance. The use of a metal cover for the O-ring is effective because it mechanically restrains the O-ring under pressure, ensuring that the seal maintains its shape and position. Metal covers provide rigidity and prevent the O-ring from being pushed out of its groove, which is a common issue under high pressures where the O-ring can deform and extrude into the clearance gap.

While other methods such as backup rings are commonly used and have their specific advantages, they are specifically designed to support the O-ring from the side that is opposite to the pressure. A split ring or gel sealant would not provide the same level of structural support needed to prevent the O-ring from being extruded by high-pressure fluids. Therefore, the metal cover stands out as the proper solution for addressing extrusion in high-pressure environments.