O-ring seal VS soft rubber ring gaskets

[Spoonful]

Hi All,

Seeking some expert advise here.

Here we got a low pressure application, around 150 kpa, water service. client to want to use as less torque as possible on the blind flange nut to create the seal. ideally finger tighten. we are planing to use some soft rubber ring gaskets, as it would be easier to create the seal at low compressive stress. or use 0 rings.

The question is which one, would expected to create the seal with less bolt torque? both rubber and o ring have the m factor of 0, meaning, they do not need a compressive stress to create the seal, and they are self-energized.

I am under the impression that if a o ring on the SO flange, the blind flange just need to be placed close enough to the the SO flange, so bolting stress required, when pressurized, the o-ring would just deform and fill the gap the create the seal. Where for the rubber ring gasket, you somehow have to give it a little bit of compression to seal. we can reduce the width of the rubber ring gasket to increase its compressive stress at the same bolt force, but when become too thinner, may risk of gasket blow out.

Hence the winner is o ring.

Any comments?

 

[SnTMan]

Spoonful, not sure what you are proposing, just place the O-ring between two RF flanges? If not familiar, see the Parker O-ring handbook:

http://www.parker.com/portal/site/P...7575e210VgnVCM10000048021dacRCRD&vgnextfmt=EN

Why the need for the low bolt loads?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[moltenmetal]

A rubber gasket (flat surface) does need some compressive stress to seal- just not much. They are somewhat forgiving of non-uniform bolt torque also.

An o-ring is self-energizing in that pressure energizes the seal. But an o-ring should be placed into a designed groove machined into the face of the blind flange, such that the bolting compresses the o-ring uniformly without squashing it. This eliminates the need for accurate bolt torquing, as any idiot can feel the sharp rise in torque when the metal faces come together.

 

[Sengland]

I would go for the o-ring, as stated previously it's easier to tell visually that it is assembled properly. There is a range of modified B16.5 flanges called ASA flanges that have o-ring grooves in them.

 

[SnTMan]

What I don't like about an O-ring seal is, if you properly assemble it and it leaks, tightening the bolts further will gain you ....nothing. You are done.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

The secret; good design groove / gland dimension an detail finishes as required for O-ring
Regards
r6155

 

[Spoonful]

Sorry If I made the question not clear, it is rubber ring basket on flat flange sealing face VS o-ring in grooves, and which one require less torque to create the seal.
Client want to a design that require less bolt torque as possible, ideally no tools required, by only finger tighten with wing nuts and like.

 

[SnTMan]

r6155, absolutely, both design and manufacturing, when possible.

Spoonful, I'd say O-ring then if it can be made properly. However I'd be a little wary of bolt loads that low. May seal, may not. May remain tight in service, may not.

A radial seal, rather than a face seal would be less sensitive to clamp force, it seem to me.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Spoonful]

Hi Mike,

A agree with you, especially for 0 ring seal, if the pressure is not remained, it might leak, until the pressure it back to the original level.

If I understood your term radial seal correctly, a o ring at the side of the raised face rather than on its face. And yes, it would be less sensitive to clamp load, as the seal is maintained by the tolerance build in within the spigot. But this is a more expensive option for manufacturing, more machining and thicker material.


Back to the topic, oring vs rubber ring gasket. Would you say oring required finer flatness for the non-grooved part? where rubber ring gasket can be a little more for tolerant?

 

[SnTMan]

Spoonful, yes a radial seal would seal against two concentric surfaces, rather than parallel surfaces, and yes more expensive to make.

To the topic, O-ring would not necessarily require greater degree of flatness, except for the low clamp force that is wanted. Either type gasket needs to have the mating surfaces brought into intimate contact with the gasket, and held so during operation. With either type gasket enough bolt load will (presumably) achieve this. I have real misgivings about the reliability of any gasketed joint that is merely "finger tight".

O-rings also need finer surface finishes and tighter manufacturing tolerances than is normally used in conventional gasketed joints. Might not be a problem for smaller parts in free-machining materials, but it might in larger parts or difficult to machine materials.

Recommend you review the Parker handbook, especially on face seals. Very useful info.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

The secret Nº 2: for O-ring, hardly lubrication on contact surfaces
Regards
r6155

 

[SnTMan]

r6155, "hardly"? Care to clarify?

Thx

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

For O-ring, only little quantity of lubricant on contact surfaces.
Regards
r6155

 

[SnTMan]

r6155, ah, just what it said

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

Secret Nº3: for O-ring, the roughness of surface shall be measured. Surface finish values shall be obtained by several readings.
Regards
r6155