The Nimrod Review - Official Documents

5.7
Figure 5.6: FRS Coupling Technical Diagram
Chapter 5 – Leak from Fuel Coupling
Research by the manufacturers of FRS seals, Eaton Aerospace, has shown that large numbers and types of RAF
and civilian aircraft have been, and are, currently fitted with the same kind of elastomeric fuel seal as used on
the Nimrod fleet. In total, an estimated 13,000 aircraft have been fitted with FRS110 couplings, of which over
half are still in service.
Avimo couplings
5.8
Two types of Avimo couplings are used within the Nimrod: the Avimo ‘Original’ and the Avimo ‘O’ ring Type
MR8610. Prior to fitting an Avimo original coupling, grooved sleeves are welded or brazed onto the pipe ends.
The Avimo Original coupling comprises a rubber seal fitted over the pipe ends and retained by two semi-circular
metal shells held in place by a jubilee clip. The seals used in the Avimo Original couplings were manufactured
from polychloroprene (often referred to as Neoprene). In 2008, however, it was discovered that, since 2000,
the Avimo seals have been made from a Neoprene compound which does not match exactly the required
material specification, provoking early degradation (discussed later in this Chapter). As a result, the seals are
now manufactured from a Nitrile material similar to that used in the FRS coupling.
Figure 5.7: Avimo Coupling Assembly
FRS and Avimo couplings in the starboard No. 7 tank dry bay
There are eight
5.9 FRS couplings and one Avimo Original coupling in the starboard No. 7 Tank Dry Bay. They are all
located higher than the Cross-Feed/Supplementary Cooling Pack (SCP), ducts.
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