Fuel, Hydraulic & Chemical-Zone Sealing

EPDM and butyl, with ePTFE and FFKM as the broad-spectrum escalations. Phosphate-ester fluids in the SAE AS1241 class attack the fluorocarbon and nitrile families that own the rest of the wet zones: FKM, fluorosilicone, and NBR all swell and degrade.

EPDM (RE-series foam and the MIL-R-83285 class solid) is the structural default; butyl covers conformable seams at ambient; ePTFE sheet is inert for bolted joints; and FFKM (AMS7257 class) keeps elastomer behavior where the joint also sees hydrocarbons. Ratings are qualitative per each family's TDS; verify your specific fluid brand and temperature. [2]

Because the two zones run on inverted compatibility maps. The families that hold up in jet fuel and mineral oils (FKM, fluorosilicone, nitrile, HNBR) are attacked by phosphate-ester hydraulic fluid, and the families that tolerate phosphate esters (EPDM, butyl) swell rapidly in fuel and oil. One part number cannot serve both unless it comes from the both-map families: FFKM (AMS7257 class) or ePTFE sheet.

That inversion is the single most expensive lesson in aircraft fluid sealing, which is why the compatibility wheel on this page shows each family's whole map at once. [1]

Fluorosilicone sponge in the AMS 3323 class is the conformable default: closed-cell, fuel-stable per the ASTM D471 immersion data on its TDS, and flexible through altitude cold soak where nitriles stiffen. For clamped flanges that want a solid, AMS 3215 class nitrile carries the legacy designation economically, and FKM (AMS 3216 class) takes the hot end.

Die-cut to the fastener pattern with the bolt-hole web widths the panel actually allows, and write the full fluid list (fuel type, icing inhibitor, cleaning solvents) on the drawing so the immersion screening covers reality. [3]

When temperature or aging exceeds what the NBR TDS supports. Standard AMS 3215 class nitrile is the economical answer at cool fuel and mineral-fluid joints. As the joint approaches gearbox and accessory heat, HNBR's hydrogenated backbone buys a wider window and better oxidative aging at moderate cost. Sustained heat, hot ester turbine oils (MIL-PRF-23699 class), and long inspection intervals push to FKM, whose AMS 3216 class TDS covers the hot end of the hydrocarbon map.

Read each family's immersion and aging data at your actual joint temperature; the matrix's headroom column orders them for exactly this walk. [8]

No, and the difference decides real joints. Fluorosilicone (FVMQ, the AMS 3323 sponge class here) is a silicone backbone with fluorinated side groups: it keeps silicone's low-temperature flexibility and conformability and adds fuel stability, but gives up the hot-oil endurance and toughness of true fluorocarbons.

FKM (the AMS 3216 / MIL-R-83248 class) is a fluorocarbon elastomer: harder working at heat, stronger, the flange-gasket material, but stiffer at deep cold. Rule of thumb: cold-soaked, wavy, low-closure-force fuel joints lean fluorosilicone sponge; hot, clamped, oil-wetted flanges lean FKM. Neither survives phosphate esters. [4]

It defines the material by specification rather than brand: AMS 3323 fluorosilicone sponge, AMS 3216 / MIL-R-83248 fluorocarbon, AMS 3215 nitrile, MIL-R-83285 EPDM, AMS7257 FFKM. The converter's job is to source stock whose TDS carries the called designation and to ship the lot-coded documentation that proves it; the design holder's job is everything above that. When a legacy drawing names both a brand and a designation and they disagree, the designation wins and we flag the conflict at quote.

If your quality flow-down needs specific cert formats from the material maker, put it on the RFQ and we quote to it.

That trajectory is the signature of fluid swell. An elastomer absorbing the wrong fluid expands first, which packs the joint tighter and briefly improves the seal; then the swollen, softened material loses mechanical integrity, extrudes from the flange, takes massive set, and the joint opens. By the time it leaks, the gasket cross-section often looks visibly grown or gummy.

The fix is chemistry, not torque: identify the fluid that reached the gasket (including the one from the system next door), rerun the family selection on this page's wheel, and replace with the right map's material.

Re-tightening a swelling gasket buys weeks and worsens the extrusion. [1]

Glycol-based de-icing and anti-icing fluids are gentle on the right families and persistent on everything: they wash leading edges, sills, hinge lines, and whatever sits downstream, repeatedly through every winter rotation. EPDM is the natural fit (glycol tolerance plus UV and ozone endurance per the TDS data), with butyl covering conformable seams. Silicone families also tolerate glycols, so dry-zone parts that catch overspray are usually fine.

The honest concern is the mixture case: a de-icing-washed sill that also catches fuel or hydraulic weep needs the cross-contamination logic, not the glycol logic. Map where the fluid travels after it hits the airframe, not just where it lands.

As an engineering review, never a catalog pick. Oxygen service is governed by a different evaluation framework (ASTM G63 is the reference guide for nonmetallic materials): ignition sensitivity, autoignition behavior, and cleanliness matter as much as chemical compatibility, and a chemically "fine" gasket can be dangerous if it arrives with shop-handling hydrocarbon residue.

The directional starting points are PTFE-class materials and specifically assessed fluorinated elastomers; the process requirements are oxygen-clean handling and packaging with documentation.

H-O converts the material your review selects and packages to the cleanliness flow-down; the oxygen-compatibility assessment itself belongs to the system designer. [10]

When the fluid list defeats every elastomer map, and the joint is bolted. ePTFE is essentially inert across this page's six fluid classes per the maker's resistance data, which makes it the default for cross-contamination boundaries and mixed-chemistry manifolds. The trade is mechanical: PTFE seals by conformation and creep control under sustained, defined bolt load rather than elastic rebound, so it needs gasket stress the flange can supply and hold, retorque per the maker's guidance, and no expectation of recovering a moving joint.

Bolted flange with impossible chemistry: ePTFE. Conformable panel seal with impossible chemistry: FFKM, at FFKM prices. [11]

Yes. The FKM sheet we convert spans 1/64″ to 1/2″ (about 16 to 500 mil) per the Fluorozone TDS thickness list, with the EPDM, nitrile, and HNBR solids in comparable sheet ranges and the sponge families per their TDS gauges. Thin sponge and solid cut cleanly by steel-rule die; thick or hard sections move to waterjet, which keeps edges square without heat-affecting the elastomer; and intricate connector patterns go to CNC knife.

Washers, flange gaskets, segmented rings for large bolt circles, and kiss-cut PSA-backed sets are all standard converting formats. Send the drawing; we route it to the right cutting method and say so in the quote.

No. H-O Products is an ISO 9001:2015 certified organization that and converts fluid-zone materials for aerospace OEMs and their suppliers. Compatibility statements on this page are qualitative classifications of the immersion data the material makers publish (ASTM D471 framing) on the TDS we keep on file, and the designations cited (AMS 3323, AMS 3216, AMS 3215, AMS7257, MIL-R-83285) are the classes those TDS documents carry.

Seal-level qualification against your fluid, temperature, and life requirement belongs to the design holder's test program. We supply the converted parts, the lot-coded documentation, and an honest screening direction; your coupons and rigs supply the proof.

H-O is a die-cutter and converter, so every gasket is made-to-order to your drawing, including samples. We maintain working material relationships with the fluorosilicone, FKM, nitrile, EPDM, and ePTFE makers and keep common stocks on hand for faster turnaround.

Samples typically ship in 3–5 business days for common configurations on materials we keep on hand. Standard production runs ship about 2 weeks after drawing approval, including waterjet-cut thick sections and kiss-cut sets. Expedited service is available for AOG and line-stop dates. MOQ varies by material and part; prototype quantities through production runs are equally accepted. Send the drawing and quantity through the form below for a specific commitment with your quote.