Sealing Shielding

New O-Ring Materials for Jet Fuel Lengthen Maintenance Cycles and Reduce Costs

New Seals & O-Ring Materials for Jet Fuel ApplicationsFor years, fluorosilicone rubber has been the go-to seal material for jet fuel applications in the aerospace industry. It offers good resistance to jet fuel with outstanding low temperature properties (sealing down to -100°F) and thermal stability up to 350°F. But, O-rings made of this material have to be replaced yearly or any time the engine comes in for any other maintenance or repair. As one engine manufacturer said, ideally, O-rings would last an entire C-check cycle (about 5 years for most aircraft). Fluorocarbon O-rings consistently do that, but only seal down to about -35 or -40°F.  Spring-energized PTFE lip seals are a potential alternative, but this usually means the joint has to be completely re-engineered.

Parker now offers two new elastomer materials for longer-lasting O-rings that can handle jet fuel and maintain a reliable seal over the critical application temperature range of -65 to +300°F. 

Next-generation fluorosilicone

Parker’s next generation fluorosilicone, LM100-70, meets AMS-R-25988 and MIL-DTL-25988 specs and offers considerable savings without the engineering expense of material specification changes. Most fluorosilicone seal applications begin to leak because the O-ring takes a compression set—it permanently flattens out and no longer makes good contact with the mating surfaces.

A two-week lab test comparing standard fluorosilicone materials with LM100-70 (see Table 1) showed that performance of Parker’s material far surpasses “generic” materials, which can permanently lose more than half the amount they are squeezed. Although some functional testing is needed to say exactly how much longer LM100-70 lasts in real-world applications, this performance correlates to a significantly improved service life.

 

 Compression Set

 336 hours @ 302°F

 M25988/1-214 O-ring

 Standard fluorosilicone

 53%

 LM100-70

 10%

Table 1: LM100-70 compared with generic fluorosilicone

New extreme low temperature fluorocarbon

Parker’s new extreme low temperature fluorocarbon, VX065-75, offers even greater improvements in service life and overall seal performance than LM100-70. This new technology far surpasses even the lowest temperature fluorocarbon compounds currently on the market.

A ballpark estimate (see Table 2) shows the financial impact of extending the service life of elastomer seals in fuel applications. (This example is for a single O-ring that is replaced four times over a 5-year C-check period.)

 

 Cost Per Seal

# of Seals

 Extended Cost

 Replacement O-rings

 $0.30

4

 $1.20

 Installation Labor

 $100 per hour * 0.1667 hour

4

 $66.67

 Downtime

 $10,000 per hour * 0.1667 hour

4

 $6,666.67

 Total

 

 

 $6,734.54

Using seals made from VX065-75 to extend seal service life to a typical 5-year C-check offers a significant savings opportunity. Even if a single VX065 O-ring cost an absurd $3,000 (don’t worry, it’s actually closer to $3), the maintenance savings would still be astronomical.

Conclusion

Standard fluorosilicone O-rings and seals have long been used to seal jet fuel, but dramatically improved service life is possible with Parker’s new extreme low-temperature fluorocarbon, VX065-75. Service life improvements are also possible with Parker’s next generation fluorosilicone, LM100-70. Both options can significantly reduce the maintenance cost associated with replacing seals before regularly scheduled C-check inspections.

 

Seals & O-Rings, New Materials by Parker Hannifin O-Ring Division

 

 

This article contributed by Dan Ewing, Senior Chemical Engineer, Parker Hannifin O-Ring Division.

 

 

 

 

Related Content:

What You Should Know About Advanced Bonding Technology

Aerospace Technologies and Key Markets

 

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