Rubber: Fluorocarbon Elastomer (FKM) 70 to 80 Hardness, Low Temperature Sealing Tg -50 °F (-46 °C) For Elastomeric Seals in Aircraft Engine Oil, Fuel and Hydraulics Systems
This specification covers high temperature, compression set and fluid resistant fluorocarbon elastomer material to be used in the form of O-rings, compression seals, O-ring cord, and molded-in-place gaskets for aeronautical and aerospace
These products have resistance to a variety of gas turbine engine oils, including high thermal stability (HTS) oils, fuels,
and hydraulic fluids, but usage is not limited to such applications. Each application should be considered separately. This fluorocarbon (FKM) has a service temperature range of -65 to +400 °F (-54 to +204 °C) in air.
1.3 Safety - Hazardous Materials
While the materials, methods, applications, and processes described or referenced in this specification may involve the
use of hazardous materials, this specification does not address the hazards, which may be involved in such use. It is the
sole responsibility of the user to ensure familiarity with the safe and proper use of any hazardous materials and to take
necessary precautionary measures to ensure the health and safety of all personnel involved.
FKM fluoroelastomer material) technology has advanced since AMS 7379 was written for Low Temperature Sealing Tg -40 F ( -40 C)
New generation of FKM can now achieve Tg -50 F ( -46 C)
True alternative to NBR or low temperature needs below - 65 F (-54 C ) since MILPRF-87257 fluid, the low temperature limit shall be –65 °F (-54 °C).
Boeing supports the development of this specification (Dan Zierten). The industry does not have a seal material which meets the long standing AS5440 “Hydraulic Systems, Military Aircraft, Design and Installation, Requirements For” specification which has had the following requirements which relate to temperature for many many years:
Type I Maximum fluid operating temperature +160 °F (+71 °C).
Type II Maximum fluid operating temperature +275 °F (+135 °C).
3.6.1 Fluid Temperature Limitations
Fluid temperatures shall not exceed +160 °F (+71 °C) for Type I systems and +275 °F (+135 °C) for Type II systems at any point in the system. Operation at these temperatures shall not result in any degradation of the system. With MILPRF-87257 fluid, the low temperature limit shall be –65 °F (-54 °C).
To date, traditional Nitrile ages and hardens when operated over 240F and then leaks at lower temperatures and traditional fluorocarbons tend to leak below -40F.
The industry does not have a seal material which provides good performance over life when operating over the AS5440 temperature range for a Type II system (which is the most common type used in military applications).