Quick answer: A spring-energized seal is a precision-engineered sealing device that uses a metallic spring to apply continuous contact force through a polymer jacket. It is the correct choice when an elastomeric O-ring cannot survive the service conditions — specifically cryogenic temperatures below −60°C, ultra-high vacuum below 10⁻⁶ mbar, aggressive chemicals that attack every elastomer, or precision dynamic motion requiring extremely low friction. The jacket is most commonly PTFE, but PEEK and UHMWPE are used for specialized pressure, wear, or purity requirements. The spring is the heart of the design: it compensates for jacket cold flow, wear, and thermal contraction so the seal maintains force without relying on elastic recovery.
This guide covers the jacket materials, spring types, load curves, temperature and pressure limits, chemical resistance, groove design rules, and application selection for spring-energized seals. If you are evaluating whether to upgrade from an O-ring or encapsulated O-ring, see our related comparisons on spring-energized seals vs O-rings and encapsulated O-rings vs spring-energized seals.
What Are Spring-Energized Seals?
A spring-energized seal (SES) consists of two functional parts:
- Polymer jacket — the process-contact sealing element, most often machined PTFE in a U-cup, lip, or C-ring profile.
- Metallic energizer spring — installed inside the jacket and applies a defined contact force between the jacket lip and the mating surface.
Unlike an elastomeric O-ring, which depends on the elastic recovery of compressed rubber, a spring-energized seal depends on the spring for force. The jacket provides the chemical barrier and low-friction sealing surface; the spring provides the mechanical compliance. This separation of functions is what allows SES technology to operate where elastomers fail.
Spring-energized seals are manufactured by machining the jacket from PTFE rod or tube stock, installing the spring, and then finishing the seal to the specified groove dimensions. Because they are machined rather than molded, they are almost always custom-built to the application. Lead times are typically 3–6 weeks, with minimum order quantities of 5–10 pieces for custom sizes. For standard catalog requirements, standard O-ring products remain the faster and lower-cost option.
Jacket Materials: PTFE, PEEK, UHMWPE, and Filled PTFE
The jacket material determines the seal's chemical compatibility, temperature limit, friction, wear rate, and load capacity. PTFE is the default choice, but PEEK and UHMWPE are specified when mechanical properties or purity requirements demand them.
PTFE jacket grades
| Jacket Grade | Filler | Max Temp | COF (Dry) | Wear Resistance | Best Application |
|---|---|---|---|---|---|
| Virgin PTFE | None | +260°C | 0.05–0.08 | Low — high cold flow | Pharmaceutical, semiconductor, food, UHV |
| 15% glass-filled PTFE | Glass fiber | +260°C | 0.06–0.10 | Good | General dynamic reciprocating seals |
| 25% carbon-filled PTFE | Carbon | +260°C | 0.04–0.07 | Excellent | Dry-running rotary seals |
| Carbon + graphite PTFE | 15% C + 5% graphite | +260°C | 0.04–0.07 | Excellent | Self-lubricated dynamic service |
| 60% bronze-filled PTFE | Bronze | +260°C | 0.08–0.15 | Very high | Heavy-load hydraulics, heat sinking |
| PEEK-filled PTFE | PEEK | +260°C | 0.06–0.10 | Very good | High-pressure static, hard surfaces |
Virgin PTFE offers the broadest chemical resistance and lowest coefficient of friction, but it creeps significantly under load. Filled grades trade a small amount of chemical resistance for dramatically improved wear resistance and dimensional stability. For dynamic service, a filled grade is almost always specified. For static service where chemical purity is critical — such as semiconductor or pharmaceutical process equipment — virgin PTFE is the required material.
PEEK and UHMWPE jackets
| Material | Temp Range | Key Properties | Typical Use |
|---|---|---|---|
| PEEK | −70°C to +250°C | High modulus, excellent creep resistance, steam-compatible | High-pressure steam, autoclaves, load-bearing static seals |
| UHMWPE | −200°C to +80°C | Very low friction, high impact resistance, FDA grades | Food processing, water hydraulics, low-temp dynamic |
| PTFE composites | −270°C to +260°C | Best chemical resistance, lowest friction, moderate wear | Cryogenic, chemical, vacuum, general dynamic |
PEEK jackets are selected when the seal must resist mechanical deformation under high load or high-pressure steam. UHMWPE is used when FDA compliance, low cost, and impact resistance matter more than high-temperature capability. Neither PEEK nor UHMWPE matches PTFE's universal chemical resistance, so media compatibility must be verified before specifying them.
Spring Types: Cantilever, Canted Coil, and Helical
The spring type defines the load-deflection behavior of the seal. Choosing the wrong spring type is one of the most common causes of SES field failures.
Spring type comparison
| Spring Type | Load Profile | Deflection Range | Friction | Best Application |
|---|---|---|---|---|
| Cantilever (single-turn) | Moderate, relatively flat | Limited | Low | Precision face seals, instrumentation valves |
| Canted coil | Near-constant over wide range | Wide | Very low | Dynamic reciprocating, rotary, semiconductor |
| Helical (garter) | High force, rising rate | Moderate | Moderate | High-pressure static, slow dynamic |
| V-spring | Very high, stiff | Limited | Higher | High-pressure static seals, wellhead valves |
| Nested V-spring | Highest force | Very limited | High | Extreme-pressure static, high-temperature |
Cantilever springs are a single continuous strip formed into a ring, with flexible fingers pressing outward. They are simple, cost-effective, and provide a consistent force over a small deflection range. They work well in face seals and light dynamic applications but are less tolerant of wear or large thermal movements.
Canted coil springs are the most common choice for dynamic service. Each coil is tilted relative to the seal axis, which produces a flat load curve: as the jacket wears or cold-flows, the spring deflects further but the contact force changes very little. This self-compensating behavior makes canted coil SES ideal for long-stroke reciprocating seals, rotary feedthroughs, and semiconductor wafer handling equipment.
Helical garter springs are formed from a coiled wire joined into a circle. They deliver higher force than canted coil springs but with a steeper load curve, meaning small changes in groove dimension create larger force variations. They are commonly used in high-pressure static seals where high initial contact force is required.
V-springs and nested V-springs provide the highest contact forces and are used when pressure loads are extreme. The trade-off is higher friction and limited deflection range, which makes them unsuitable for high-speed dynamic service.
How Spring-Energized Seals Work: The Load Curve
The sealing performance of an SES is governed by the relationship between spring force, jacket geometry, and system pressure.
When the seal is installed in the groove, the spring is partially compressed. This preload creates an initial contact stress between the jacket lip and the mating surface. As system pressure increases, pressure acts on the inner face of the jacket, pushing the lip harder against the sealing surface. This pressure-energization effect is similar to how an O-ring is energized by pressure, but the spring provides the baseline force that makes sealing possible at vacuum or very low pressures.
The ideal load curve has three characteristics:
- Adequate initial contact stress — typically 0.05–0.30 MPa at assembly — to seal at low pressure and vacuum.
- A flat spring curve — so contact stress does not fall excessively as the jacket wears or cold-flows.
- Pressure energization — system pressure increases contact stress proportionally above the spring preload.
| Seal Parameter | Typical Value | Effect on Performance |
|---|---|---|
| Initial contact stress (canted coil) | 0.05–0.20 MPa | Low friction; seals vacuum and low pressure |
| Initial contact stress (helical/V-spring) | 0.20–0.50 MPa | Higher sealing force; higher friction |
| Pressure-energized contact stress at 200 bar | 2–8 MPa | Dominates at high pressure |
| Deflection reserve | 15–40% of spring travel | Compensates for wear and cold flow |
PTFE cold flow is the main reason the spring is necessary. Under sustained contact load, PTFE creeps permanently. In a solid PTFE seal, that creep would reduce contact force to zero. In a spring-energized seal, the spring expands to follow the creeping jacket and maintains contact force. For more background on PTFE behavior, see our PTFE O-ring complete guide.
Temperature Range: From Cryogenic to +260°C
Spring-energized seals span the widest temperature range of any commercial sealing technology.
| Spring Material | Minimum Temp | Maximum Temp | Notes |
|---|---|---|---|
| 302/304 stainless steel | −196°C | +315°C | General industrial and mild chemical |
| 316 stainless steel | −196°C | +315°C | Better chloride resistance |
| 17-7 PH stainless steel | −196°C | +315°C | Higher spring force retention |
| Elgiloy (Co-Cr-Ni) | −270°C | +550°C | Cryogenic and corrosive service |
| Hastelloy C-276 | −270°C | +430°C | Chloride and acid environments |
| Inconel 718 | −270°C | +650°C | Aerospace, high-temperature cryogenic |
The jacket almost always sets the upper temperature limit. PTFE, PEEK, and UHMWPE are all limited to approximately +260°C, +250°C, and +80°C respectively. The spring sets the lower temperature limit. With metallic springs, cryogenic service down to −270°C is routine. This is the defining advantage for liquid helium, hydrogen, nitrogen, oxygen, and LNG systems.
For guidance on selecting seals for low-temperature service, see cryogenic O-ring selection. For high-temperature seal materials above +200°C, spring-energized PTFE is often compared against FFKM and specialized metal seals.
Pressure Capability
Spring-energized seals operate across an exceptionally wide pressure envelope.
| Service Condition | Pressure Range | SES Configuration |
|---|---|---|
| Ultra-high vacuum | 10⁻⁹ torr and below | Virgin PTFE, canted coil or cantilever spring |
| Medium vacuum | 10⁻³ to 10⁻⁶ torr | Virgin or filled PTFE, metal spring |
| Low pressure / atmospheric | 0–10 bar | Canted coil for dynamic; cantilever for static |
| Moderate pressure | 10–200 bar | Canted coil or helical, filled PTFE for dynamic |
| High pressure | 200–700 bar | Helical, V-spring, or nested V-spring |
| Extreme pressure | 700+ bar | Nested V-spring, PEEK jacket, tight clearance |
At high pressure, the SES must be designed so that spring preload plus pressure-energized force exceeds the separation force trying to lift the jacket lip away from the sealing surface. The groove must also prevent jacket extrusion into clearance gaps. In ultra-high-pressure service, PEEK jackets or PTFE backup rings may be added alongside the SES to support the jacket against extrusion.
Chemical Resistance
The chemical resistance of a spring-energized seal is determined almost entirely by the jacket material. PTFE provides the broadest resistance of any commercial polymer.
| Chemical Family | Virgin PTFE | Filled PTFE | PEEK | UHMWPE |
|---|---|---|---|---|
| Strong acids (HCl, H₂SO₄, HNO₃, HF) | Excellent | Excellent to good | Good | Good |
| Strong bases (NaOH, KOH, NH₃) | Excellent | Excellent to good | Good | Good |
| Organic solvents (ketones, esters, aromatics) | Excellent | Excellent | Good | Good |
| Oxidizing agents (H₂O₂, ozone, ClO₂) | Excellent | Good | Fair | Good |
| Steam / hot water | Excellent | Excellent | Excellent | Good |
| Petroleum oils and fuels | Excellent | Excellent | Excellent | Good |
| Chlorinated solvents | Excellent | Good | Good | Good |
| Molten alkali metals, F₂, ClF₃ | Not suitable | Not suitable | Not suitable | Not suitable |
For environments where even FFKM has limits, PTFE is often the only elastomeric-type seal option. However, FFKM remains a simpler and lower-cost solution for many aggressive chemical applications. See our comparison of Kalrez vs Chemraz vs FFKM for context on when a perfluoroelastomer O-ring may be preferable.
Groove Design for Spring-Energized Seals
Spring-energized seals require application-specific groove geometry. A standard O-ring groove cannot be used without modification.
Groove design parameters
| Parameter | Typical Requirement | Notes |
|---|---|---|
| Groove width | Jacket width + running clearance | Must allow lip deflection and spring travel |
| Groove depth | Sets spring deflection and preload | Defined by seal supplier drawing |
| Corner radius | 0.3–0.5 mm minimum | Prevents jacket cutting during assembly |
| Lead-in chamfer | 20–30° over 2–3 mm | PTFE cannot be stretched like elastomer |
| Surface finish (dynamic) | Ra 0.1–0.25 µm | Same as precision elastomer dynamic seals |
| Surface finish (static) | Ra 0.4–0.8 µm | Less critical than dynamic |
| Clearance gap | Tight — typically 0.05–0.20 mm | Prevents jacket extrusion |
The groove depth is the most critical dimension: too shallow and the spring is under-deflected, producing insufficient contact force; too deep and the spring over-deflects, increasing friction and accelerating wear. Always work from the seal manufacturer's groove drawing.
PTFE elongation at break is 250–400%, much lower than elastomers. SES installation requires folding or compressing the jacket into the groove, not stretching it over a sharp edge. Generous lead-in chamfers and installation sleeves are required to prevent jacket damage.
Spring-Energized Seal vs O-Ring vs Encapsulated O-Ring
| Factor | Elastomeric O-Ring | Encapsulated O-Ring | Spring-Energized Seal |
|---|---|---|---|
| Temperature range | −60°C to +300°C (VMQ to FFKM) | −55°C to +205°C | −270°C to +260°C |
| Cryogenic service | No | No | Yes |
| Ultra-high vacuum | Marginal | Limited to ~10⁻⁶ Torr | Yes, to 10⁻⁹ Torr |
| Dynamic service | Good | Poor — FEP jacket abrades | Excellent with filled PTFE |
| Chemical resistance | Material-dependent | Near-PTFE at surface | Near-universal with PTFE |
| Friction coefficient | 0.15–0.30 | 0.30–0.60 | 0.04–0.10 |
| Groove | Standard AS568/ISO | Standard AS568/ISO | Custom groove required |
| Relative cost | Low | Moderate | High (10–100× O-ring) |
| Lead time | 3–7 days stock | 7–15 days | 3–6 weeks custom |
Choose an elastomeric O-ring for standard industrial, hydraulic, automotive, and process applications where temperature, pressure, and chemistry are within elastomer limits. Choose an encapsulated O-ring for static chemical service in existing standard grooves where the FEP/PFA jacket provides chemical protection. Choose a spring-energized seal when service conditions exceed all elastomeric options: cryogenic temperatures, ultra-high vacuum, universal chemical attack, or ultra-low-friction dynamic motion. For a deeper comparison, read encapsulated O-rings vs spring-energized seals.
Applications by Industry
Semiconductor
Semiconductor process equipment requires seals that are chemically inert, low-outgassing, low-friction, and particle-free. Spring-energized PTFE seals with virgin PTFE jackets and canted coil springs are standard for wafer handling, chemical delivery modules, vacuum chambers, and valve seats. Outgassing rates below 10⁻⁹ mbar·L/(s·cm²) are achievable with virgin PTFE.
Cryogenics
Liquid nitrogen (−196°C), liquid oxygen (−183°C), liquid hydrogen (−253°C), and liquid helium (−269°C) all require metallic-spring SES. No elastomer remains functional at these temperatures. Elgiloy or Inconel 718 springs are standard for the coldest services.
Oil and gas
Spring-energized seals are used in subsea connectors, wellhead valves, BOP systems, and cryogenic LNG transfer. In these applications they often replace metal seals where some compliance is needed, or complement PTFE backup rings in high-pressure valve packing.
Aerospace
Aerospace applications include cryogenic propellant seals, high-temperature pneumatic systems, and vacuum-rated hardware. Inconel 718 springs are preferred for their combination of cryogenic toughness and high-temperature strength.
Medical and pharmaceutical
FDA-compliant virgin PTFE spring-energized seals are used in surgical instruments, drug delivery devices, analytical pumps, and sterilizable equipment. The low-friction, non-stick surface reduces actuation force and eliminates elastomer extractables.
Related Technical Guides
- Spring energized seals vs O-rings
- Encapsulated O-rings vs spring energized seals
- PTFE O-ring complete guide
- High-temperature seal materials
- Cryogenic O-ring selection
- Kalrez vs Chemraz vs FFKM
- PTFE encapsulated O-ring guide
- Spring-energized seals product page
- PTFE products
- PTFE backup rings
FAQ
Q1: What is the main advantage of a spring-energized seal over an O-ring?
The spring provides continuous contact force independent of elastomeric recovery. This allows the seal to function at cryogenic temperatures, in ultra-high vacuum, and across wide thermal cycles where elastomeric O-rings become rigid or lose compression set recovery. PTFE jackets also provide near-universal chemical resistance and much lower friction.
Q2: Which spring type should I choose for a dynamic reciprocating application?
Specify a canted coil spring for most dynamic reciprocating applications. Its near-constant force curve compensates for jacket wear and thermal movement without large changes in contact force or friction. For high-speed or dry-running rotary service, canted coil with carbon-filled PTFE is also the standard choice.
Q3: Can spring-energized seals be used in rotary applications?
Yes. Canted coil spring-energized seals are commonly used in rotary feedthroughs, valve stems, and precision rotary joints. PTFE's low friction coefficient minimizes heat generation, and the canted coil spring maintains consistent lip contact as the jacket wears asymmetrically.
Q4: What spring material is best for cryogenic service?
For liquid nitrogen and liquid oxygen, 17-7 PH or Elgiloy springs are standard. For liquid hydrogen and liquid helium, Elgiloy or Inconel 718 are preferred because they retain spring characteristics and fatigue resistance at the lowest temperatures. Avoid standard 302/304 stainless in liquid hydrogen or helium service due to embrittlement concerns.
Q5: Why does the jacket material matter more than the spring for chemical resistance?
The jacket is the only component in continuous contact with the process fluid. The spring is enclosed within the jacket and is protected from direct chemical exposure. Therefore, chemical compatibility is determined by the jacket material. PTFE provides the broadest resistance; PEEK and UHMWPE are selected for specific mechanical or purity requirements.
Q6: Can I install a spring-energized seal in a standard O-ring groove?
No. Spring-energized seals require a custom groove profile designed around the jacket width, spring deflection, and lip geometry. Installing an SES in an O-ring groove will result in incorrect preload, possible jacket damage, and unreliable sealing. Groove dimensions must come from the seal manufacturer.
Q7: How do filled PTFE grades affect spring-energized seal performance?
Fillers improve wear resistance, reduce cold flow, and increase load capacity. Glass-filled PTFE is common for general dynamic service. Carbon-filled PTFE is preferred for dry-running and rotary applications. Bronze-filled PTFE handles the highest mechanical loads but is not suitable for oxidizing acids. Virgin PTFE remains the choice for maximum chemical purity and lowest outgassing.
Q8: When should I choose PEEK instead of PTFE for the jacket?
Choose PEEK when the seal must resist high-pressure steam, autoclave sterilization, or mechanical loads that would cause PTFE to cold-flow excessively. PEEK has much better creep resistance and higher modulus than PTFE. However, PEEK does not match PTFE's chemical inertness or low friction, and its low-temperature limit is higher.
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Need spring-energized seals for cryogenic, vacuum, or high-pressure service? Request a quote with your groove dimensions, operating temperature, pressure, fluid media, and motion type. Our engineering team specifies jacket grade, spring type, and spring material for your application. We manufacture custom spring-energized PTFE, PEEK, and UHMWPE seals with MOQ as low as 5 pieces and 3–6 week lead time. For standard applications, contact us to compare elastomeric and spring-energized options.