High Pressure O-Rings

High Pressure O-Ring Materials:

The system operating pressure is always a consideration as it effects the choice of seal materials in several ways.

Hardness (Durometer)

First is hardness, as may be required to resist extrusion in dynamic designs or where there is a large gap between sealed members in static applications. At very low pressures, proper sealing may be more easily obtained with lower durometer hardness (50-60 shore A). With higher pressures, the combination of pressure and material shore hardness determine the maximum clearance that may safely be tolerated.

Second is at-rest vs operating conditions and requirements for “leakless” at rest conditions which would suggest due consideration be given to the long-term compression set properties of a given material.

O-ring Extrusion

Extrusion of O-rings may also be prevented by the use of anti-extrusion (back-up) devices. These are thin rings of much harder material fitted into the gland between the seal and the clearance gaps, which essentially provide zero clearance. They are available in hard elastomer compounds, leather, PTFE, Nylon and other similar materials. Parker Parbaks® are elastomer back-up rings and are generally recommended based on their proven functional superiority. The exact point at which it becomes necessary to use anti-extrusion devices will depend on the pressure, type of elastomer being used, its Shore hardness, the size of the clearance gap, and the degree of “breathing” of the metal parts which will be encountered.

Limits of Extrusion
*chart courtesy of Parker O-Ring Handbook (ORD 5700)

Parker Urethane (AU) O-Ring Compound:

Parker Urethane (AU) O-Ring Compound:

Brand Parker Compound Number Datasheet Hardness (Shore A) Low Temp High Temp Color Recommended For
Parker P0642-70 PDF 70 +- 5 -40 180 Black Drive Belt Applications, Millable

High Pressure PTFE Materails:

Material Description Service Temp °F Tensile Strength at Break (psi) Hardness Shore D
Virgin PTFE Excellent for Cryogenic applications. Good for gases -425 to 450 4500 60
Modified PTFE Lower creep, reduced permeability and good wear resistance. -320 to 450 4600 60
Mineral Filled PTFE Excellent low abrasion to soft surfaces & improved upper temperature performances. FDA Materials. -360 to 550 4070 65
Fiberglass Filled PTFE Excellent compressive strength and good wear resistance. -200 to 575 3400 67
Fiberglass & Molly Filled PTFE Excellent for extreme conditions: high pressure & temperature & for longer wear life on hardened dynamic surfaces -200 to 575 3100 62
Graphite Filled PTFE Excellent for corrosive service. Low abrasion to soft shafts. Good in unlubricated service. -250 to 550 3200 60
Carbon-Graphite Filled PTFE Excellent wear resistance and reduces creep. -360 to 575 2200 64
Bronze Filled PTFE Excellent extrusion resistance and high compressive loads. -200 to 575 3200 63
Carbon Fiber Filled PTFE Good for strong alkali and hydrofluoric acid. Good in water service. -200 to 550 3200 60
Aromatic Polyester Filled PTFE Excellent high temperature capabilities & excellent wear resistance -200 to 575 2500 61