Help With a Leaky BSPP Fitting??

JohnC

Missing a few cylinders
Lifetime Supporter
I have a leak in a high pressure hydraulic circuit at a BSPP male plug fitting. This plug is the type that has a machined recess for the o-ring, and there was a square cross section o-ring there. It looked flatter than it should have, so I replaced it with a round section o-ring from a Dowty seal and it still leaked.

Next I replaced the plug fitting with another type that simply had a large flat sealing surface, and I used a Dowty fitting on it, which leaked, then a plastic washer with a much larger surface area than the Dowty and it leaked too.

Since I've now tried two different fittings and three different types of seals, I'm thinking it's not the fittings that have a problem, but the female port that I'm trying to plug.

I've got some Stat-o-Seals arriving tomorrow, but if those don't hold, my options are narrowing down quickly.

Anyone ever used thread sealer or teflon tape on these fittings? I realise with a BSPP fitting, the threads aren't supposed to do the sealing, the o-ring is, but in my case it's not, so I'm looking at all alternatives.
 

Russ Noble

GT40s Supporter
Lifetime Supporter
Sounds like not enough crush on the o ring John. Have you tried a slightly thicker o ring?

Naturally you have checked the machined surfaces are not damaged etc.
 

JohnC

Missing a few cylinders
Lifetime Supporter
Cheers Russ & good to hear from you.

I did swap the first square section o-ring out for a thicker round one. I may try an even larger one, however. Thought the plastic washer would do the trick, but no joy with it.

I've visually inspected the surfaces, and didn't see any damage, but that doesn't mean much with my vision. I really need to get a closeup view with a strong light. I'll put my trusty digicam on macro and see if that picks up anything on the o-ring sealing surfaces. I've found its lens is far better than my eyes for closeup work.
 

JohnC

Missing a few cylinders
Lifetime Supporter
Found the culprit with the help of the digicam. The inner threads for the fitting came too high and interfered with the chamfer surface for the o-ring. So the o-ring doesn't have a full, unbroken surface to seat against. Hmmm.

I've put the plastic washer back on the fitting, then put the square o-ring on after that, so the o-ring will fit down in this semi-groove, tweaked it back up, pressured the system and am waiting to see if it weeps.

IMG_3527Custom.jpg
 
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