Keeping separable fluid fittings secure can be a challenge. Here are a few helpful tips.
When failure is not an option
Mission-critical applications such as jet-engine-fuel manifolds typically incorporate a secondary locking mechanism to secure fluid fittings. Lockwire was once the method of choice and still finds use in many cases. But lockwire is widely recognized as a leading cause of foreign object damage (FOD). It's also difficult to maintain and only minimizes the chance of loosening, but doesn't prevent it. This is because (ideally) lockwire is not installed in tension. Lockwire can fatigue crack and fail in some cases, especially when it is under tension. For these reasons, many newer military weapons systems specify "no lockwire."
Other secondary locking techniques for fluid fittings include safety cable (similar to lockwire but made from cable with crimpedon ends), thread-locking compounds, deformed threads, clips, and tab washers. Most of these products can't be reused, and clips and tab washers are yet another potential FOD source.
Fuel manifolds for PW127 turboprop engines from Pratt & Whitney Canada Corp., use Moeller Click-Loc technology on the fluid couplings. Fingerlike springs made of Inconel 718 engage a multitooth cam of the same material on the mating fitting, securely locking the two halves together.
Click-Loc secondary locking technology can be integrated into fittings or added to existing ones. Click-Loc-equipped fittings can be reused 100 times or more before replacement and have a perfect record of reliability (no failures) in hundreds of millions of component service hours.
Photo: Jean Claude Belanger
Moeller Mfg. Co. Inc., www.moelleraircraft.com