Most elastomeric seals are designed to operate to about 1,500 PSI. At very high pressures, the seal must avoid extrusion into the clearance. There are several strategies that can be used to allow the o-ring to seal at higher pressures. How much pressure an o-ring can handle depends on several factors:
- Clearance (Extrusion Gap)
- O-Ring Durometer
- Backup Rings
- Static vs. Dynamic Applications
The relationship between fluid pressure, clearance, and durometer is expressed visually in the graph to the right.
Techniques to avoid extrusion in high-pressure applications include decreasing the clearance gap, increasing the durometer, and adding a backup ring(s).
Clearance (Extrusion Gap)
As a general rule, the lower the clearance, the higher the pressures the o-ring can tolerate before being extruded. The wider the clearance, the higher the probability for the o-ring to be extruded. High pressure and high clearance together create the worst scenario for the o-ring to maintain its form and function. For more information on o-ring groove design, click here.
High-durometer o-rings are better suited for higher pressures and are more resistant to extrusion. Hard material yields higher pressure required to force the o-ring into extruding. The only drawback to a high durometer is the decreased squeeze of the o-ring.
With backup rings providing added extrusion resistance, the gap is all but eliminated to allow essentially zero clearance. If high pressure is coming from one direction, a single backup ring should suffice when placed on the low-pressure side within the gland. If high pressure is coming from both directions, two backup rings (one on each side of the o-ring) are recommended. Backup ring materials include Buna (NBR), Viton® (FKM), PTFE, PEEK, and Nylon.
Static vs. Dynamic Applications
O-Rings can withstand higher pressures in static applications compared to dynamic applications. In dynamic applications, if the friction of the moving metal surface across the o-ring is in the same direction as the pressure, the o-ring can potentially be dragged into the gap. This can occur at less than half the pressure of what it normally takes to cause extrusion.
If you would like more information about o-rings and/or backup rings in regards to your high-pressure application, please give us a call at 832-448-5550 or submit a contact form with your specifications.