Sealing AN flare Fittings using O-Rings

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Well-Known Member
HMEM Supporting Member
Jan 26, 2022
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I use AN-10 flare fittings on my boiler's input and output connections and have experienced more than a few problems with leaky connections. No matter how much torque I apply, I almost always get a small leak. Smaller AN sizes, such as AN-4 & AN-6 connectors, almost never leak, but I always had problems with the larger AN-10,...but not any longer.

Using my lathe, I cut a small channel into the beveled face of the male flared end as shown below:
AN-10 O-ring channel.jpg

The channel is large enough to hold a 16 or 17mm (OD) x 1.5mm O-Ring as shown below with the Red silicone O-Ring on the right side of the pic.
Boiler Out Sensor Block sml.jpg

I recently pressure tested my modified AN-10 fittings with O-rings up to 800 psi with no sign of leaks. As an added bonus, the connection seals using only minimal tightening torque :)