Female flare to pipe fitting?

I have a vacuum pump with a flare cross fitting (two 3/8" and what looks like 1/8" flare). This fitting is very well set in the pump and I could not unscrew it with about 50 ft lbs of force (guesstimated). I do not want to use more force and would prefer to get an adapter. Something like 3/8" flare to 1/4" NPT. The catch is that the adapter must be female flare, not male, as it usually happens. I looked in usual placed like our local hardware store and McMaster, and did not find much. Any suggestions?

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Just flare a bit of copper tubing and silverbraze it to a 1/4" NPT fitting. 1/4" NPT is too leaky for good vacuum but it might work OK with pipe dope down to 1 torr or so.

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Don Foreman

As I recall, your pump looked like it was an HVAC pump, so you may need to locate parts from HVAC sources. Are you sure it is 3/8"? R-12 and several other refigerants used 1/4" flare. I looked around the various Internet sources I have for automotive AC and the only pump adapters they offer are 1/4" female flare.


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My guess is that someone used Loctite on the fitting. Heat is what's needed to kill the bond, if that's the case. Heat it until it smokes, then it should be good to go once it's cooled down. What you have for a fitting sounds like what I had to get for my pump when I adapted it to automotive A/C use. Might not be a standard pipe or flare fitting thread, would explain the lack of success finding fittings. You can get vacuum hoses for the automotive A/C fittings for gauge sets and adapters from those to NPT, you'd have to look on the web at the various car A/C supplier sites to find what you need, though. Autozone and some of the other chain parts places do carry a limited selection of A/C fittings, might not match what you have, though.


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What angle is the flare, 37 or 45 degrees (relative to the centerline) and what thread size 1/2-20, 9/16- 18, etc? I'd be surprised if Mcmaster doesn't have an adapter. For instance, if they are 37 degree fittings then page 248 with the SAE J514 hydraulic hose swivels will fit.

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