Why is a Teflon backup ring used when pressure is over about 1500 psi?

Why is a Teflon backup ring used when pressure is over about 1500 psi?

• A. To seal better
• B. To reduce friction
• C. To improve heat transfer
• D. To prevent extrusion of the O-ring

Answer: (D)

When a seal is pressed by high pressure, the elastomer O-ring can be forced to flow into the clearance gap between the mating surfaces, causing extrusion and a leak. A Teflon (PTFE) backup ring placed in the seal groove provides a rigid barrier that resists that flow. It bears most of the pressure on the O-ring side and prevents the O-ring from being squeezed out into the gap, so the seal stays intact even at higher pressures like around 1500 psi. This is the primary purpose of a backup ring. The other options describe less relevant effects—the backup ring isn’t mainly for making the seal itself better, reducing friction, or improving heat transfer.

When a seal is pressed by high pressure, the elastomer O-ring can be forced to flow into the clearance gap between the mating surfaces, causing extrusion and a leak. A Teflon (PTFE) backup ring placed in the seal groove provides a rigid barrier that resists that flow. It bears most of the pressure on the O-ring side and prevents the O-ring from being squeezed out into the gap, so the seal stays intact even at higher pressures like around 1500 psi. This is the primary purpose of a backup ring. The other options describe less relevant effects—the backup ring isn’t mainly for making the seal itself better, reducing friction, or improving heat transfer.