O-Ring Installation/Uses

[badazz81z28]

I took adapters off my Wilwood hydraulic clutch MC and noticed there was an O-ring on the NPT fitting for the remove reservoir. The interesting thing, this O-ring is too wide to be internal. Seems it was used more as a gasket. Is this a proper use of an O-ring? I was thinking maybe the OD should be smaller and fit around the ID of the hole. Thoughts?

[MrQuick]

is it a metal ring?

[exwestracer]

There was a period of time where a lot of plumbing fittings used NP-S (national pipe- straight) fittings rather than the typical NPT or AN bolt thread type. Those would typically have a "stat-o-seal" at the face. If the female thread has a large countersink at the top, it may use a simple o-ring that is pressed down into the countersink as the fitting is tightened. An o-ring should never be used to seal face to face without one of these 2 retention methods.

If the fittings are NPT (tapered), the o-ring is redundant and pretty much useless....

[badazz81z28]

There was a period of time where a lot of plumbing fittings used NP-S (national pipe- straight) fittings rather than the typical NPT or AN bolt thread type. Those would typically have a "stat-o-seal" at the face. If the female thread has a large countersink at the top, it may use a simple o-ring that is pressed down into the countersink as the fitting is tightened. An o-ring should never be used to seal face to face without one of these 2 retention methods.

If the fittings are NPT (tapered), the o-ring is redundant and pretty much useless....

That's basically how it's used. Its on my Keisler Hydraulic Clutch Set-up on a Wilwood Master Cylinder. The threads are not tapered and this O-ring is used as a face to face seal. Here is a Picture.

[badazz81z28]

Here is the MC. Keep in mind the O-rings OD is way too large to fit in that hole.

[badazz81z28]

Well, Looks like according to Wilwood, the hole is 7/16"-20 thread. I sent them an email to ask what the correct O-ring size is for the hole. The One Keisler provides is way to wide to fit in the hole, but it did seal before when it was on the car...so who know...But I do need a new O-ring.

[MIKE67]

O-rings can swell when exposed to fluids. I disassembled a damaged Bilstein shock and the rod seal was ridiculously large. There was no way to put it back into the housing. After it sat out for several months, it was close to it's original size.