HP seal surfaces

[guruboy]

Curious to know more details about HP seal requirements. Specifically, how the contour of the sealing surfaces affect the ability of the oring to seal.

Let's take the seal between tank neck and valve. Quote below was taken from another thread.

On an aluminum tank the recess for the o-ring is milled into the tank neck and is more or less square in cross section and provides surfaces for the o-ring to seal. On a steel tank this recess is more of a cone shaped shoulder so the anlges and seatign surfaces are a bit different.

However in either case, when the valve is installed properly, the valve comes into metal to metal contact with the tank neck and fully contains the o-ring. If there is no gap between the metal surfaces, there will be no extrusion of the o-ring and it will not leak as it is fully supported.

What happens if the recess on the tank where the o-ring sits is irregular shaped? For example, what if it was shaped like a gear/cog instead?

Can the o-ring still seal as long as there is metal to metal contact with no chance of extrusion?

 

[redacted]

If an O-ring does not make good contact with the sealing surface, the seal may be compromised.

 

[Belzelbub]

The sealing surface needs to be smooth in order to provide a good seal. The other surfaces can be shaped like a cog, but I don't know why you'd want to do that. It could provide a bit better retention when not engaged, but won't help with sealing at all.

In the cases of the tank necks, you'd likely not want to do that, but if it was done in an area that was not a sealing surface, it wouldn't hurt.

 

[guruboy]

So the o-ring needs a surface to seal against, even if it can't extrude.

What if it's just a tiny scratch/dent on the corner on the tank o-ring groove?


So the o-ring can still make a good seal with the side of the tank o-ring groove and the bottom of the valve, but there's a small defect in the corner between them.

(red star is the scratch/dent)

 

[KeithG]

Curious to know more details about HP seal requirements. Specifically, how the contour of the sealing surfaces affect the ability of the oring to seal.

Let's take the seal between tank neck and valve. Quote below was taken from another thread.



What happens if the recess on the tank where the o-ring sits is irregular shaped? For example, what if it was shaped like a gear/cog instead?

Can the o-ring still seal as long as there is metal to metal contact with no chance of extrusion?

Google parker Hannigan oring handbook. It has lots of good info about using orings as seals.

 

[KeithG]

Google parker Hannigan oring handbook. It has lots of good info about using orings as seals.

Parker hannifin

 

[guruboy]

Will do. thanks

 

[Belzelbub]

So the o-ring needs a surface to seal against, even if it can't extrude.

What if it's just a tiny scratch/dent on the corner on the tank o-ring groove?

In your example, that scratch/dent isn't in a place that is part of the sealing surface, so it shouldn't cause any issues by itself.

 

[guruboy]

so the critical surfaces are the side of the tank o-ring groove and the bottom of the valve?

 

[Belzelbub]

so the critical surfaces are the side of the tank o-ring groove and the bottom of the valve?

In this case, yes. Primarily since we are talking about round cross-section o-rings. In other applications, the corners may come into play, but not in this case.