Quick Answer: How can you reduce seal weight in aircraft engine applications?
Reducing seal weight in aircraft engine applications comes down to three decisions: material, geometry, and sourcing. Polytetrafluoroethylene (PTFE) spring-energized lip seals deliver meaningful weight savings over traditional metallic designs without compromising performance under pressure, heat, or chemical exposure.
When original equipment manufacturer (OEM) seals go obsolete, custom-engineered replacements can be designed to drop in without system modifications. And when supply chain risk threatens aircraft-on-ground (AOG) situations, in-house manufacturing capability is what separates a fast solution from a long wait.
A mechanical seal is not the most glamorous component in an aircraft engine. It rarely shows up in program reviews, and nobody writes a press release about it. But when one fails — or can't be sourced at all — you feel it fast. Grounded aircraft, halted production lines, and AOG situations that nobody budgeted for.
The challenge with aerospace mechanical seals isn't just performance. It's the combination of extreme operating conditions, shrinking OEM supply chains, and the fact that many platforms are still flying on seal designs specified decades ago. When that original part number disappears from the catalog, someone has to figure out what comes next.
This guide addresses three problems aerospace OEM and maintenance, repair, and overhaul (MRO) design engineers deal with regularly: how to reduce seal weight without sacrificing reliability, how to replace a discontinued OEM seal without redesigning the surrounding system, and how to structure a supply chain that doesn't leave you exposed when lead times stretch and parts dry up.
Weight reduction in aircraft engine design is never one big win. It's a hundred small ones. Mechanical seals are exactly that kind of opportunity: individually light, but present in enough quantity across an engine and its associated systems that the aggregate adds up. Every gram saved in a rotating assembly improves thrust-to-weight ratio, reduces fuel burn, and compounds over the operating life of the aircraft.
Traditional metallic seals — steel, aluminum alloy, heavy-section elastomeric designs — carry more mass than most applications actually require. The engineering tradeoff made sense when the alternatives weren't as mature. Today, PTFE-based and spring-energized seal designs have a track record in demanding aerospace environments that justifies a closer look.
PTFE has a density advantage over metallic alternatives, but that's almost beside the point. The reason it belongs in aerospace seal applications is the combination: low friction, chemical inertness, thermal stability across a wide temperature range, and performance that holds up under dynamic loading over a long service life.
Spring-energized PTFE lip seals add another layer. A precision-formed metal spring, typically helical or cantilever, maintains consistent lip contact force regardless of what the shaft is doing: thermal expansion, runout, or wear over time. The result is a lighter seal that actually performs better in conditions where a heavier metallic design would be over-engineered for some parameters and under-engineered for others.
Geometry is where additional weight gets cut. Custom-engineered seals can be designed to the minimum cross-section the application requires, removing material that contributes mass without contributing function. Finite element analysis (FEA) simulation of contact pressure and thermal behavior lets engineers validate a design computationally before committing to hardware, which reduces physical iteration and keeps the final design tight.
Not all PTFE is the same. Compound formulation has a significant effect on how a seal performs in a specific application, and aerospace engine environments push several variables simultaneously. A few key distinctions:
Spring material matters too. Hastelloy, Elgiloy, and 316 stainless are common choices, each suited to different combinations of media exposure, temperature, and fatigue life requirements. Published data sheets will get you most of the way there. For the edge cases, there's no substitute for working with an engineer who has run these materials in comparable conditions.
OEM seal discontinuation isn't an edge case. It's a regular occurrence, and it lands hardest on platforms with long service lives, military fixed-wing and rotary aircraft running on legacy designs, and commercial operators maintaining older engine variants. When a part number goes end-of-life, the options come down quickly: find an approved equivalent, qualify a new source, or wait.
The engineering complication is that the original specification is often incomplete or simply gone. OEM documentation doesn't always survive program transitions. In the worst cases, the only thing left is a worn physical part.
"This was complicated because we only had a used seal to replicate. This design was from scratch, and the seal was very small — .419" diameter."
— Gerald Strenk, Global PTFE Product Manager, Ergoseal
That worn part is not the end of the specification. It is the specification. Surface condition, deformation patterns, and lip geometry under load all carry information about how the original design was loaded, where it succeeded, and where it was stressed. Dimensional inspection, material identification, and wear pattern analysis together build a specification that may be more complete than the original engineering record.
Ergoseal worked through exactly this scenario with a confidential U.S. aircraft manufacturer whose critical seal, used in wheel speed sensors across both commercial and military platforms, was discontinued by its original supplier. The seal protected sensor internals from pressure, temperature fluctuation, and contaminants that feed anti-skid braking function. Without it, the braking system was at risk.
The engineering team had one used part to work from. The replacement, a spring-energized PTFE rotary lip seal at .419" diameter, was designed from scratch, manufactured and tested in-house, and delivered as a drop-in with no modifications to the customer's existing system. The new design outperformed the original on durability and gave the customer control of a supply chain they'd previously had no alternative to.
In MRO and platform-level seal replacement, drop-in fit isn't a nice-to-have. Modifying surrounding hardware to accommodate a new seal design triggers qualification work that multiplies cost, time, and paperwork. A replacement seal has to meet or exceed the original performance specification within the existing envelope, full stop.
That demands precision on several fronts simultaneously:
AS9100D certification establishes the quality management framework that aerospace customers require as a starting point. Design control, material traceability, test documentation, corrective action — these aren't bureaucratic overhead. They're the process infrastructure that makes a replacement seal qualifiable, not just manufacturable.
Military fixed-wing seal replacement comes with layers of complexity that commercial programs don't face to the same degree. Platform service lives routinely exceed original design intent. Maintenance is performed against technical orders referencing part numbers that may no longer exist at any approved source. Documentation and qualification requirements are correspondingly rigorous.
The operating environment compounds this. Military aircraft span a wider range than commercial platforms: arctic ground operations, high-altitude flight, sustained exposure to hydraulic fluids and lubricants that vary across long service periods. A replacement seal specification has to account for all of it, not just the nominal mission profile.
“Unlike a typical industrial application where material certification and dimensional verification may be sufficient, this type of project requires full material traceability, lot-level documentation, and full validation against the applicable military and aerospace specifications,” explains Lazarus Adamidis, Ergoseal Business Operations Manager.
“In addition to meeting dimensional and functional requirements, we are required to provide a comprehensive documentation package that includes raw material certifications, manufacturing and process records, inspection reports, shelf-life controls, first-article inspection data, and other customer and program-specific quality deliverables.”
For operators managing legacy military platforms, that documentation burden isn't bureaucratic overhead; it's the proof of airworthiness.
A seal that can't be fully traced and validated isn't a solution, regardless of how well it fits.
AOG (aircraft on ground) is the operational condition every MRO director and procurement team is built to prevent. When a seal is the proximate cause, the root cause is almost always upstream: single-source dependency, no qualified alternative, inadequate safety stock, or a supplier discontinuation that wasn't flagged until someone needed the part.
Seal supply chain risk is easy to underestimate because the seals themselves are inexpensive relative to the systems they protect. That math changes instantly in an AOG scenario. The cost of a grounded aircraft has nothing to do with the unit price of the seal. It's measured in aircraft-down hours, expediting costs, contract penalties, and, for military operators, mission readiness that can't be quantified on a spreadsheet.
OEM seal supply chains have consolidated significantly over the past decade. Mergers, program exits, and manufacturing rationalization have reduced the number of approved sources for many aerospace seal part numbers. Operators who once had competitive multi-source options increasingly find themselves with a single approved supplier, often the OEM or their designated licensee.
When that single source extends lead times, raises prices, or discontinues a part, there's no fallback. And the qualification of an alternative takes exactly the time an AOG situation doesn't have.
The practical response is proactive diversification: identifying and qualifying alternative seal sources before a supply event forces the issue. For custom or engineered seals, that means finding a manufacturer with in-house design, engineering, and production capability, someone who isn't dependent on their own sub-tier suppliers to deliver on short notice.
Custom and low-volume aerospace seal lead times can stretch to weeks or months under normal backlog conditions. Standard aerospace is not a fast-moving supply chain, and seal manufacturers managing material procurement and qualification paperwork aren't optimized for urgency.
In-house capability across design, manufacturing, and testing compresses that timeline by eliminating handoffs. A manufacturer who designs the seal, cuts the PTFE, forms the spring, assembles, and tests without outsourcing any stage of production can respond to urgent requirements that a distributed supply chain simply cannot match.
For MRO planning, the smarter question isn't how fast a replacement can be made. It's how to avoid that situation entirely. Safety stock programs, long-term supply agreements with qualified manufacturers, and proactive qualification of alternative sources before OEM discontinuation all address the risk before it becomes a crisis.
There's an efficiency argument for supply chain consolidation that goes beyond AOG risk. Aerospace operators and OEMs managing multiple seal suppliers for different seal types — face seals, lip seals, spring-energized PTFE, rotary seals — carry qualification overhead, documentation complexity, and engineering interface friction for each relationship. That adds up.
A manufacturer with demonstrated capability across seal types and aerospace applications can consolidate that burden. Accumulated application knowledge, design familiarity with your systems, and a single quality management relationship all reduce the friction of ongoing seal engineering and procurement.
The wheel speed sensor case study above is a concrete example of what that looks like: a spring-energized PTFE rotary lip seal designed from a worn part, qualified as a drop-in replacement for a discontinued OEM seal in an aircraft braking system. That outcome required design competence, manufacturing capability, and the kind of persistent problem-solving that a catalog order doesn't provide.
For design and application engineers evaluating a custom or replacement aerospace mechanical seal, the following is a practical qualification framework. A downloadable one-page version of this checklist is available at the link below.
Bore diameter, shaft diameter, and housing depth confirmed against the worn part or original drawing
Running clearances and tolerance stack documented for dynamic applications
Feature requirements identified: retention grooves, anti-rotation, venting
Operating temperature range defined, including transient conditions, not only nominal
Media compatibility confirmed: hydraulic fluid type, lubricant, fuel, moisture exposure
Pressure differential across the seal face documented
Shaft speed and surface finish requirements established for rotary lip seals
Leakage rate specification defined
Service life expectation and replacement interval established
Torque or friction limitations identified, particularly relevant for spring-energized designs
Supplier AS9100D certification confirmed
Material certificates and traceability available
Test documentation in place: dimensional inspection and functional test results
Design documentation sufficient to support the customer's qualification process
Ergoseal designs and manufactures custom PTFE lip seals, spring-energized PTFE lip seals, and mechanical face seals for aerospace and demanding industrial applications. AS9100D and ISO 9001:2015 certified, with engineering, manufacturing, and testing capabilities in-house from initial application review through fabrication and qualification support.
For aerospace OEM and MRO engineers working on weight-reduction programs, obsolete seal replacement, or supply chain risk mitigation, Ergoseal's engineering team engages directly with the application — not the catalog.
Have an aerospace seal application? Get in touch with our team.