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For the true gurus...what is this o-ring.
1 Attachment(s)
I've attached a Vans Aircraft photo of inlet and outlet fitting they sell for the Lycoming mechanical fuel pump. These fittings screw into the fuel pump with a straight thread that incorporates an o-ring. I believe the same o-ring is used on each fitting.
I want to replace my o-rings. Does anybody here know authoritatively (not guessing) what spec these o-rings are. I suspect they are either an MS29513-112 or they could be an MS29512-06. Or these could be interchangeable. Vans doesn't seem to list these o-rings as spares. Feedback would be appreciated. Attachment 273 |
According to Spruce, it’s a MS 29513-111.
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Maybe check with Tom at TS Flightlines.
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I replaced mine recently. They aren’t actually milspec. Although it references multiple MS part numbers on aircraft spruce website, an inquiry directly with spruce resulted in the part number 3-906 NBR
You can purchase these from you local bear / seal shop. Once again, not a milspec seal. Hope this helps |
A variety box of viton o rings should get you the size you need. Summit, jegs, Russel, etc. all sell these straight thread to AN adapters and they all use generic viton o rings.
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Lycoming lists them as MS29512-06, but that was an old number. Most certainly from a different material now, since the fuel additives probably have changed. Industrial fittings use an elastomer/viton/buna neoprene---or did.
I dont recall hearing of any fuel leakage with a stock o'ring, and I'll bet most arent changed at conditional inspections. Tom |
Why do you want to change yours? Is it leaking? As noted, I don't think anybody (or most anybody) messes with these at annual CIs, other than to ensure they're still tight.
If it ain't broke, don't fix it... |
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O-rings
I use the MS29512-06 o-rings on those. Check for loose connections between the tanks and the fuel pump. A loose connection on the suction side can sometimes leak air but not fuel. Look at all your tubing flares and make sure they are not cracked or not flared properly, or even over tightened and damaged. Fuel pressure fluctuations are not that uncommon and sometimes its a sender or indication problem. Also an old fuel pump (5-6 yrs) can cause that problem because the diaphragms get stiff and the check valves and springs get weak.
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For the true gurus...what is this o-ring.
The GAHCO catalog lists the MS29513-XX as "Aircraft fuels/Standard sizes" and the MS29512-XX as "Aircraft fuels/Boss sizes".
For the fuel pump fittings you are showing, these are "boss sizes" in that the o-ring is trapped between the flat end of the fitting (or nut and washer for adjustable angle types) and a chamfer in the straight thread female component (MS33649). So the MS29512-XX is the correct specification for these fittings. Incidentally any AN fitting has an unthreaded shank next to the nut and can also be used with these o-rings in a "boss type" straight thread female component. Selected sizes are: O-ring Tubing Nominal OD O-ring ID MS29512-03 3/16 0.301 MS29512-04 1/4" 0.351 MS29512-05 5/16 0.414 MS29512-06 3/8 0.468 MS29512-07 7/16 0.530 MS29512-08 1/2 0.644 MS29512-09 9/16 0.706 MS29512-10 5/8 0.755 Updated specs, for example AS5202 use a 900 series o-ring number. Parker's numbering for this series goes from 3-901 through 3-932. These o-rings are also used in the SAE J1926 industrial straight thread tube fittings. In the typical sizes used in our airplanes the o-rings and fitting thread sizes are: O-ring Thread Size O-ring ID 3-901 .250"-28 0.185 3-902 .312"-24 0.239 3-903 .375"-24 0.301 3-904 .437-20 0.351 3-905 .500-20 0.414 3-906 .562-18 0.468 3-907 .625-18 0.530 3-908 .750-16 0.644 3-909 .812-16 0.706 3-910 .875-14 0.755 The elastomer compounds are suitable for aircraft fuels (avgas, jet-a etc.) so trying to substitute a viton compound is not necessary. |
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