Fluorosilicone (FVMQ) O-Rings
The only material that combines silicone's -60°C low-temperature flexibility with fuel and oil resistance for aerospace and automotive fuel systems.
Overview
FVMQ (Fluorosilicone, also called FSI or MFQ) is a silicone elastomer in which methyl side groups are partially replaced by fluorinated alkyl groups — typically trifluoropropyl (-CH₂CH₂CF₃). This modification transforms standard VMQ silicone from a material with poor fuel resistance into one that tolerates petroleum oils, gasoline, jet fuel, and aromatic hydrocarbons while retaining silicone's signature wide temperature flexibility.
FVMQ O-rings operate from -60°C to +175°C continuous — a 235°C span that no other fuel-resistant elastomer achieves. Standard FKM (Viton) handles fuel to +200°C but becomes stiff below -20°C. Standard VMQ silicone remains flexible to -60°C but swells excessively in fuel. FVMQ bridges this gap: it is the only elastomer that seals reliably in aerospace fuel systems experiencing both arctic ground temperatures and hot-soak engine-bay conditions.
Typical fluorine content of 23–30% by weight provides resistance to aliphatic and aromatic fuels, petroleum-based oils, and synthetic hydraulic fluids. Volume swell in ASTM Reference Fuel B (isooctane/toluene) is typically 10–25% for FVMQ versus 100–200% for standard VMQ — the difference between a functional seal and a failed one.
FVMQ is most commonly specified in blue color, which has become an industry convention for fluorosilicone seals in aerospace and military applications. The blue pigment provides visual traceability and distinguishes FVMQ from black FKM and red VMQ in mixed-inventory environments.
Limitations: FVMQ tensile strength (5–9 MPa) and tear resistance remain low — comparable to standard VMQ. It is not suitable for high-pressure dynamic sealing without backup rings. Acid and base resistance is inferior to FKM. Cost is 3–5× standard VMQ and 2–3× FKM.
Lead time: 10–20 days; 3–5 days for stocked sizes. MOQ: 1 piece. ISO 9001 certified. MIL-PRF-25988 and SAE AMS-R-83485 grades available.
Sizes and tolerances: FVMQ O-rings are molded in all standard AS568 inch sizes and ISO 3601 / DIN 3771 metric sizes, plus custom cross sections and inside diameters for non-standard grooves. Standard tolerance follows ISO 3601-1 Class B unless otherwise specified; tighter tolerances are available for aerospace fuel fittings where squeeze must be controlled to maintain both low-temperature sealing force and assembly load limits.
Compound options: the standard offering is a blue, 70 Shore A peroxide-cured fluorosilicone meeting ASTM D2000 FK callouts. Hardnesses from 50 to 80 Shore A cover most static fuel applications — softer 50–60 Shore A compounds maximize conformability at low temperature and low squeeze, while 75–80 Shore A compounds improve extrusion resistance in higher-pressure fittings. MIL-PRF-25988 and SAE AMS-R-83485 compounds are supplied with full lot traceability, material test reports, and certificates of conformance.
Selection checklist — choose FVMQ when all of the following are true: the fluid is a hydrocarbon fuel, petroleum oil, or synthetic lubricant; service temperatures drop below -20°C (where FKM stiffens); the seal is static or low-duty-cycle dynamic; and acid, base, or ketone exposure is not expected. If temperature never falls below -20°C, FKM is usually the more economical and chemically broader choice. If fuel resistance is not required, standard VMQ delivers the same low-temperature flexibility at roughly one-third the cost.
Material Properties
| Temperature Range | -60°C to +175°C (-76°F to +347°F); short-term to +200°C |
| Hardness Range | 50–80 Shore A (ASTM D2240) |
| Tensile Strength | 5–9 MPa (ASTM D412) |
| Elongation at Break | 100–400% (ASTM D412) |
| Compression Set (70 h/150°C) | ≤ 35% (ASTM D395 Method B) |
| Low-Temperature Flexibility (TR10) | -55°C to -60°C (ASTM D1329) |
| Fluorine Content | 23–30% by weight |
| Color (standard) | Blue (industry convention) |
| Compliance | MIL-PRF-25988, SAE AMS-R-83485, ASTM D2000 FK |
Typical Applications
Aerospace
Jet fuel system static seals, fuel line couplings, and APU seals where -40°C cold-start flexibility and jet fuel resistance are both required per MIL-PRF-25988.
Automotive
Fuel injector seals, fuel rail O-rings, and evaporative emission system seals in direct-injection gasoline and diesel engines.
Military
Tactical vehicle fuel system seals and Arctic-grade hydraulic seals meeting SAE AMS-R-83485 for extreme cold climate operations.
Aviation Ground Support
Fuel dispensing equipment, hydrant couplers, and refueling nozzle seals exposed to both jet fuel and wide ambient temperature swings.
Marine
Outboard motor fuel system seals and small-craft fuel line fittings where salt air, UV, and fuel contact coexist.
Chemical Compatibility Summary
Compatible With
- - Gasoline and diesel fuels
- - Jet fuel (Jet A, JP-4, JP-8)
- - Petroleum-based oils
- - Synthetic lubricants
- - Silicone oils and greases
Incompatible With
- - Concentrated acids
- - Strong bases and amines
- - Ketones and esters
- - Hot water and steam
- - Abrasive slurries
Key Advantages
Widest Temperature Range of Any Fuel-Resistant Elastomer
FVMQ spans -60°C to +175°C with fuel resistance — a combination no other elastomer achieves. FKM handles fuel to +200°C but stiffens below -20°C; NBR handles fuel to +120°C and embrittles below -30°C. FVMQ is the only material for aerospace fuel seals that must start reliably after overnight exposure at -40°C and then seal against hot fuel at +100°C.
Excellent Fuel and Oil Resistance with Silicone Flexibility
Trifluoropropyl side groups provide resistance to gasoline, jet fuel (Jet A, JP-4, JP-8), diesel, and synthetic lubricating oils. ASTM D471 volume swell in fuel is 10–25% versus 100–200% for standard VMQ. FVMQ maintains the low glass transition temperature (Tg ≈ -65°C) of silicone, ensuring seal conformability at cryogenic and arctic conditions.
Superior Low-Temperature Performance vs FKM
TR10 of -55°C to -60°C means FVMQ retains elastomeric sealing force at temperatures where FKM has become a rigid solid. In aerospace fuel systems, this is the difference between a leak-free cold-start and fuel weeping past a stiffened seal during engine startup at altitude or in arctic bases.
Aerospace and Military Grade Certifications
FVMQ compounds are available to MIL-PRF-25988 (military fluorosilicone rubber) and SAE AMS-R-83485 (aerospace fluorosilicone) with full lot traceability, material test reports, and certificates of conformance. These specifications control tensile strength, elongation, compression set, fuel resistance, and low-temperature flexibility within tight bands.
Color-Coded Visual Identification
Blue is the industry-standard color for FVMQ O-rings, providing immediate visual differentiation from black FKM, red VMQ, and brown FKM seals in maintenance operations. This color convention is widely adopted in aerospace, military, and automotive industries to prevent material mix-ups in fuel system service.
Good UV and Ozone Resistance
The siloxane backbone retains the inherent UV and ozone resistance of standard silicone. FVMQ seals tolerate years of outdoor exposure without surface cracking, making them suitable for aircraft parked on tarmacs, military vehicles in desert environments, and marine fuel systems.
Frequently Asked Questions - FVMQ
What is the difference between FVMQ and standard VMQ silicone?
FVMQ (fluorosilicone) is VMQ silicone with fluorinated alkyl side groups added to the polymer backbone. Standard VMQ has excellent temperature range (-60°C to +230°C) but poor fuel resistance — it swells 100–200% in gasoline and jet fuel. FVMQ retains the wide temperature range (-60°C to +175°C) while reducing fuel swell to 10–25%. The trade-off is slightly higher cost (3–5× VMQ) and lower acid/base resistance than FKM. FVMQ is the correct choice when both low temperature AND fuel resistance are required.
When should I choose FVMQ over FKM?
Choose FVMQ when the application requires fuel resistance combined with low-temperature flexibility below -20°C. FKM handles fuel to +200°C but becomes too stiff for reliable sealing below -20°C (TR10 ≈ -15°C). FVMQ seals reliably to -60°C. Typical FVMQ applications: aerospace fuel systems, arctic military vehicles, and automotive fuel injectors in cold climates. Choose FKM when the temperature is above -20°C and chemical resistance to acids, bases, or ketones is also required — FKM has broader chemical resistance than FVMQ.
Are fluorosilicone O-rings available in colors other than blue?
Blue is the industry convention and most common color for FVMQ, but other colors are available on request. Black, brown, and custom colors can be produced for specific color-coding systems. However, blue is strongly recommended for aerospace and military applications because it is the recognized visual identifier for fluorosilicone in maintenance manuals and supply chains.
What is the pressure limit for FVMQ O-rings?
FVMQ has low tensile strength (5–9 MPa) and tear resistance — similar to standard VMQ. For static seals without backup rings, the practical pressure limit is approximately 10–15 bar in a well-toleranced groove. Above 15 bar, use PTFE anti-extrusion backup rings. FVMQ is not recommended for dynamic reciprocating or rotary service above 5 bar due to its poor abrasion resistance. For high-pressure fuel sealing, consider spring-energized PTFE seals or FKM with appropriate groove design.
Do FVMQ O-rings meet aerospace and military specifications?
Yes. We supply FVMQ O-rings to MIL-PRF-25988 and SAE AMS-R-83485 specifications with full material certification. These standards control: tensile strength (≥ 5.5 MPa), elongation (≥ 150%), compression set at 150°C (≤ 35%), fuel resistance (volume swell in ASTM Reference Fuel B), and low-temperature brittleness (pass at -55°C). Each lot includes a certificate of conformance referencing the specification, compound designation, and test results.
Is FVMQ compatible with synthetic lubricants and hydraulic fluids?
FVMQ is compatible with petroleum-based oils, synthetic hydrocarbon lubricants (PAO, ester-based), and phosphate ester hydraulic fluids (Skydrol) — unlike standard VMQ which swells in these fluids. FVMQ is also compatible with silicone-based fluids and greases. It is not compatible with concentrated acids, strong bases (amines, caustic), or ketones (MEK, acetone) — for these chemicals, specify FKM or FFKM.
Can I replace a standard VMQ O-ring with FVMQ in a fuel application?
Yes — FVMQ is the direct upgrade when a silicone seal is needed in fuel contact. The dimensions are identical (AS568 and ISO 3601 sizes are interchangeable), and FVMQ uses the same groove design as VMQ. However, verify that the fuel type is within FVMQ's compatibility range (gasoline, jet fuel, diesel, mineral oil). FVMQ should not be used as a drop-in replacement for FKM in high-temperature or chemically aggressive environments — FVMQ's acid and base resistance is inferior to FKM.
What is the shelf life and storage requirement for FVMQ O-rings?
FVMQ has excellent shelf stability due to the saturated siloxane backbone. When stored in original packaging away from direct sunlight, ozone sources, and temperatures above +40°C, FVMQ O-rings maintain properties for 10+ years. The fluorinated side groups do not introduce additional aging mechanisms. Standard storage per SAE ARP 5316 applies: sealed opaque bags, 15–25°C, <75% relative humidity, no ozone exposure.
How does FVMQ compression set compare to FKM and VMQ?
FVMQ compression set at 150°C/70h is typically 25–35% — worse than FKM (≤ 20% at 200°C) but comparable to VMQ (≤ 30% at 175°C). The higher compression set of FVMQ is a consequence of the lower crosslink density required to maintain low-temperature flexibility. For long-life static seals, this means FVMQ may require more frequent replacement than FKM in warm climates. In cold climates where FKM would fail due to stiffness, FVMQ's moderate compression set is an acceptable trade-off for functional low-temperature sealing.
What groove design should I use for FVMQ O-rings?
FVMQ uses standard AS568 and ISO 3601 groove dimensions — identical to VMQ and most other elastomers. Target 15–20% compression for static seals and 10–15% for dynamic seals. Because FVMQ has low extrusion resistance, use PTFE backup rings at pressures above 15 bar or when clearance gaps exceed 0.1 mm. Groove surface finish should be Ra 0.4–0.8 μm for dynamic service and Ra 0.8–1.6 μm for static service. Corner radii of 0.1–0.25 mm prevent O-ring nicking during assembly.
Is FVMQ the same material as FKM (Viton)?
No. FVMQ and FKM are completely different polymer families. FKM is a fluorocarbon elastomer with a fully fluorinated carbon-carbon backbone — it offers broad chemical resistance and continuous service to +200°C but loses flexibility below about -20°C. FVMQ is a fluorosilicone: a siloxane (silicon-oxygen) backbone with fluorinated side groups. It keeps silicone's flexibility to -60°C and adds fuel resistance, but its chemical resistance is narrower than FKM — acids, bases, amines, and ketones attack it. The two materials are specified for different reasons: FKM for chemical breadth and heat, FVMQ for fuel contact combined with extreme cold.
What does FVMQ stand for?
FVMQ is the ASTM D1418 / ISO 1629 designation for fluorosilicone rubber. The letters break down as: F (fluoro), V (vinyl), M (methyl), Q (silicone backbone). The same material is also designated FSI in some older U.S. specifications and MFQ in certain European documents. All three refer to a methyl vinyl silicone polymer in which some methyl side groups are replaced by trifluoropropyl groups.
Can FVMQ O-rings be used with ethanol-blended gasoline?
FVMQ tolerates low-level ethanol blends such as E10 commonly encountered in automotive fuel systems, and it is widely used in fuel system seals for exactly this service. For high-ethanol fuels such as E85, FVMQ is not the preferred material — high-alcohol fuels swell fluorosilicone significantly, and FKM is the standard recommendation for flex-fuel and high-ethanol applications. Always verify compatibility against the actual fuel composition, since aromatic content and oxygenate level both affect swell.
What sizes are FVMQ O-rings available in?
We supply FVMQ O-rings in the complete AS568 inch size series, ISO 3601 and DIN 3771 metric sizes, and JIS B 2401 sizes, plus custom-molded non-standard dimensions. Stocked 70 Shore A blue compound ships in 3–5 days for common sizes; custom sizes and certified MIL-PRF-25988 / SAE AMS-R-83485 compounds run 10–20 days. Minimum order is 1 piece for stock sizes.