X-Ring Sealing Issues and Alternatives

[Helepolis]

Hi all,

I'm currently working on reverse engineering an aviation fuel valve to troubleshoot and eliminate recurring leakage issues.
As shown in the attached image, the primary suspect is the X-ring, which sits in a groove on the poppet.

I have limited experience with X-rings, but I suspect the current design may be suboptimal.
Specifically, the geometry of the sealing face seems poorly matched to the X-ring.
The curved profile doesn't appear to provide proper "geometry" for sealing with an X-ring, and I believe a flat, perpendicular sealing face (relative to the axial motion of the poppet) would offer more consistent and reliable sealing.
In addition, the fact of the matter is that the spring applying force to the poppet, and thus to the X-ring against the sealing face, is relatively weak, which may further compromise sealing performance.
Another issue I have with this assembly is that the instructions dictates that the seal must be glued using Loctite 495, which is brittle when dried; what reasoning might lead to using a brittle glue to bond a soft/elastic material in its groove?

I'd appreciate any insights on X-ring use in face-sealing applications, and whether this setup aligns with best practices.


Best,
SD

 

[Compositepro]

In my opinion that is a very poor design using an x-ring. It would be okay with an o-ring. The lobe of the x-ring is pressing into the the crevice it is sealing and actually tending to wedge the puppet open.This crevice opens and x lose so it will eventually pinch the ring.

Switch to an o-ring. As to the glue being stiff, so is the metal. The glue cannot match both.

 

[Helepolis]

In my opinion that is a very poor design using an x-ring. It would be okay with an o-ring. The lobe of the x-ring is pressing into the the crevice it is sealing and actually tending to wedge the puppet open.This crevice opens and x lose so it will eventually pinch the ring.

Switch to an o-ring. As to the glue being stiff, so is the metal. The glue cannot match both.

Thanks for the answer and tips.
Regarding the glue, my concern isn't just the stiffness, it's the fact that it's a cyanoacrylate adhesive.
These glues are brittle and can potentially cause chemical reactions with the seal material.
As far as I know, when bonding soft or elastic materials (regardless of whether the substrate is a rigid metal or a flexible component), it's best to use a glue with matching flexibility. A brittle adhesive like cyanoacrylate can’t absorb the movement or "shocks" the seal may experience, which can lead to cracks, detachment, or premature failure.

 

[TugboatEng]

You are correct to be suspicious of the glue as well. When the glue bond breaks it forms a capillary to draw fluid through. Adding any type of hardening sealants or glues to an o-ring should be avoided as it negates the benefits of using a resilient seal.