O-rings
Spring-energized PTFE seals
A spring-energized seal is a jacket of PTFE, or another polymer, shaped as a U and loaded from inside by a metal spring. The spring does what rubber elasticity does in an O-ring: it keeps the jacket lips pressed against the rod, bore or face as the jacket wears and the parts move, and the system pressure adds to that load. It is specified where an elastomer O-ring cannot go: cryogenic and vacuum service, aggressive chemistry, high pressure, high speed and clean processes. Conquest Seal supplies spring-energized seals from the makers, quoted to the hardware print rather than to an AS568 size.
- Jacket
- PTFEvirgin or filled; UHMWPE and PEEK for wear
- Spring
- 3 typescantilever V, canted coil, helical
- Configurations
- Rod, piston, face, rotaryinternal or external pressure
- Sized to
- The hardwarenever an AS568 dash number
How it seals
The jacket is machined or molded from PTFE with a groove in its heel that holds the spring. Installed, the spring is compressed between the lips, so the lips bear on the sealing surfaces even with no pressure in the system. As pressure rises it enters the U and pushes the lips harder, which is why the seal tightens under load rather than extruding. The jacket wears slowly, and the spring keeps following it, which is the whole point of the design.
The three spring types
The spring decides the load, the deflection the seal can absorb and the friction it costs. Three types cover nearly every seal, and the makers name them the same way. The choice is the maker's or the print's; the jacket material and the spring alloy are named alongside it.
| Spring | Load character | Where it is used | Why |
|---|---|---|---|
| Cantilever V | Linear, over the widest deflection | Reciprocating rods and pistons; face seals; large diameters | Follows tolerance and wear across a long stroke; broad, flat contact |
| Canted coil | Near-constant over its deflection | Rotary and oscillating shafts; low-torque drives | Stable load through wear life; forgives an eccentric shaft; will not yield if over-compressed |
| Helical | Highest load, smallest deflection | Static face seals; cryogenic valves; slow or infrequent motion | Positive sealing where load matters more than friction and wear |
Jackets and spring alloys
Virgin PTFE is the jacket for chemistry, purity and food contact; filled PTFE jackets, with glass, carbon, graphite, bronze or molybdenum disulfide, add wear and extrusion resistance for dynamic and high-pressure service. UHMWPE jackets serve abrasive and food service where PTFE would wear, and PEEK jackets carry the highest loads and temperatures. Springs are made in stainless steels and, for corrosive or hot media, in the nickel and cobalt alloys their makers name; the medium that reaches the spring decides the alloy, and the print or the maker names it.
Rod, piston, face and rotary
A rod seal sits in a housing groove and seals against a moving rod; a piston seal sits in a piston groove and seals against the bore. A face seal sits in a flat groove and seals against a flat surface, with the spring loaded axially, and is the static and cryogenic-valve form. A rotary seal seals a turning shaft and usually carries a canted coil spring. Each is made to the groove and the shaft or bore it serves, and pressure can come from inside or outside the U, which decides which way the seal faces.
Where they are specified
Cryogenic pumps, valves and couplings where rubber has long gone glassy; vacuum chambers and gas systems where outgassing and permeation matter; chemical and semiconductor process equipment where the medium beats every elastomer; high-pressure hydraulic and gas service where an O-ring would extrude; high-speed rotary equipment where an elastomer would heat and tear; food and pharmaceutical machinery cleaned in place. In each case the print names the seal, the jacket, the spring and the hardware it fits.
What to send
The hardware print or the groove dimensions, the shaft or bore diameter and finish, the pressure and its direction, the speed and stroke, the medium and the temperature, and the maker's part number if the print carries one. Spring-energized seals are made to the hardware, so there is no dash number to quote from; the quote names the maker, the jacket, the spring and the sheet.
Related pages
Frequently asked
Is a spring-energized seal an O-ring?
No. It is a U-shaped polymer jacket with a metal spring inside, sized to the groove and the shaft or bore rather than to an AS568 dash number. It does the job an O-ring cannot do in cryogenic, vacuum, chemical, high-pressure and high-speed service.
Which spring type should I ask for?
Name the motion: reciprocating points to a cantilever V spring, rotary to a canted coil, static or cryogenic face sealing to a helical spring. The maker or the print settles it.
What is the jacket made of?
Virgin PTFE for chemistry and purity; filled PTFE for wear and pressure; UHMWPE for abrasive and food service; PEEK for the highest loads and heat.
What temperature and pressure can one take?
That depends on the jacket, the spring, the hardware and the medium, and no figure is published here; the maker's sheet for the seal you order governs.
Can Conquest supply a replacement for an existing seal?
Yes, from the maker's part number or from the hardware print and the groove dimensions. Send whichever you have and a Conquest representative replies.
Does a spring-energized seal need a backup ring?
Usually not; the spring and the jacket heel resist extrusion by design. At very high pressure the maker may specify a backup ring or a heavier jacket, and the print says so.
Related guides
Sources
Spring types, jacket materials and configurations, in our words from the makers' and distributors' descriptions (Bal Seal, Eclipse Engineering, Gallagher Seals, American High Performance Seals; read 2026-09-14); no figure taken; Solid PTFE and PTFE seal constructions (Parker® O-Ring Handbook ORD 5700, section 2, read 2026-09-14). Dimensional facts are stated in our own words; no standard's text or table is reproduced.
Parker is a trademark of Parker Hannifin Corporation. No affiliation or endorsement is implied.
Send the hardware print
The groove, the shaft or bore, the pressure and its direction, the motion, the medium and the temperature, or the maker's part number. A Conquest representative replies with the quote and the maker's sheet.
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