O-ring Guide

The leak-tight captured o-ring face seal was first incorporated into a variety of miniature 10-32 threaded pneumatic fittings in the late 1960s and early 1970s by Paul Beswick, a registered professional engineer and founder of Beswick Engineering. This novel approach to fluid power design, which was well ahead of its time, began a culture of innovation at Beswick Engineering. In succeeding years, Beswick Engineering introduced a long list of fluid power innovations and industry firsts. This history of innovation continues today as Beswick Engineering works closely with engineers at the top high technology OEMs throughout the world in developing unique solutions to fluid power control challenges.

Leaks and loose fitting connections were a common occurrence with the traditional flat gasket style fittings offered by other fluid power companies until the Beswick captured face o-ring face seal concept revolutionized the miniature fluid power industry. The Beswick captured o-ring face seal design eliminates leakage, simplifies assembly, eliminates the need for sealants, and reduces the incidence of loose fitting connections. Needless to say, the Beswick captured o-ring face seal design has become the “gold standard” in the industry. Look for the “be” logo on your fluid power products to make certain you are receiving a genuine Beswick product backed by years of experience and supported by a team of Applications Engineers. Beswick products provide the best overall value so don’t settle for anything less.

Beswick offers Buna-N as the standard elastomer on most products. Buna-N is suitable for a wide range of common applications. Do not worry if you application is not a “common” one and involves wide temperature extremes and/or corrosive gases or liquids because Beswick also offers the widest selection of elastomers in the industry.

Common O-ring Options:

O-Ring Type

Buna-N (Nitrile or NBR)

Most commonly provided in BLACK

Description: Buna-N is the standard elastomer for most Beswick products. It is the most widely used elastomer in the fluid power industry because of its favorable properties and relatively low cost. It has excellent resistance to petroleum products and can be compounded for use over a wide service temperature range. It provides excellent compression set, tear, and abrasion resistance. On the negative side, Buna-N has poor weather and ozone resistance and only moderate heat resistance.
-30°F to 250°F-34°C to 121°C

Fluorocarbon (FKM, Viton®)

Most commonly provided in BROWN or BLACK

Description: Fluorocarbon compounds are close to what could be called a universal elastomer since fluorocarbon provides resistance to a very broad range of chemicals yet is relatively low cost when compared to the excellent, but very costly, perfluoroelastomer compounds. Fluorocarbons have excellent high heat resistance. A disadvantage is performance at low temperatures. Fluorocarbons become hard at temperatures below -4°F (-20°C) however they do not fracture easily.
-15°F to 400°F-26°C to 205°C

Silicone (MQ, VMQ, PVMQ)

Most commonly provided in REDDISH ORANGE or CLEAR

Description: Silicone has exemplary high and low temperature resistance and good resistance to compression set. Generally silicone is used only for static seal applications because it has low physical strength, poor abrasion resistance and high friction. It swells considerably when exposed to petrochemicals but this is not necessarily detrimental in most static seal applications.
-65°F to 450°F-54°C to 232°C

Ethylene Propylene – Diene Monomer (EPDM, EP, EPR, EPT)

Most commonly provided in PURPLE or BLACK  

Description: Ethylene Propylene is compatible with polar chemicals that adversely affect other elastomers. It is used to seal UV curable inks and for sealing hot water and steam. It resists explosive decompression, which is a consideration in carbon dioxide applications, and has good resistance to mild acids, alkalis, silicone oils and greases, ketones, and alcohols.

-70°F to 250°F-57°C to 121°C

Fluorosilicone (FVMQ)

Most commonly provided in BLUE 

Description: Fluorosilicones provide most of the high and low temperature resistance of silicone along with resistance to petroleum oils and hydrocarbon fuels. Like silicone, fluorosilicone is generally used in static seals because of low physical strength and abrasion resistance as well as high friction. Fluorosilicone compounds are often used in aircraft fuel systems.
-100°F to 350°F-73°C to 177°C

Teflon® (PTFE)

Most commonly provided in WHITE 

Description: Teflon®is not an elastomer but it can be used as static seal if the seal joint will not be made and broken more than once or twice. Teflon®has excellent chemical resistance, inertness, heat resistance, low friction, zero water absorption, and excellent resistance to weathering.
-250°F to 450°F-160°C to 230°C

Aflas® (TFE/Propylene, FEPM)

Most commonly provided in BLACK 

Description: Aflas® provides excellent high temperature resistance along with resistance to a wide range of chemicals and high electrical resistivity. It resists hydraulic and brake fluids, lubricants, oils, transmission and power steering fluids, amine corrosion inhibitors, ozone, steam, acids, bases, alcohols, and other chemicals. A disadvantage is performance at low temperatures.
25°F to 450°F-4°C to 232°C

Perfluoroelastomer (FFKM, Kalrez®, Chemraz®)

Most commonly provided in BLACK or WHITE

Description: Perfluoroelastomer provides outstanding chemical resistance similar to Teflon® (PTFE) but unlike Teflon® (PTFE), Perfluoroelastomer is a true elastomer and therefore can be used in most traditional o-ring applications (both static and dynamic). In addition to the outstanding inertness and chemical resistance it can also handle high temperatures. The main disadvantage is high cost.
-15°F to 575°F-26°C to 302°C

NOTE: Temperature ranges shown are approximate. Actual temperature performance is a function of the specific elastomer compound, chemical exposure, and other factors.

Technical data obtained from:
Richards, J.E., H.G. Coates, J. Wilcox, C.Hudson. National O-Rings Engineering Manual
National O-Rings, 1982.

Registered Trademarks referenced are:
Viton®- E.I. DuPont De Nemours & Co.
Teflon®- E.I. DuPont De Nemours & Co.
Aflas®- Asahi Glass Co., Ltd
Kalrez®- E.I. DuPont De Nemours & Co.
Chemraz®- Greene Tweed