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Old 11-01-12, 05:13 AM   #1
ctpres 
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Presta question

When you secure the valve nut does it mechanically stop or does it pull core up tighter against seal?
If tighter then seal would be damaged over time if nut closed overly thight (which is what I do). Reason I ask is because about 1,000 miles ago I installed a tube with stem to short for presta air chuck. I had to use schrader adapter which I decided to leave on with nut loose enough to add air. One month later new tube needs air weekly and the other almost daily. Newer tube uses only air pressure to seal and is holding air better than any tube I can remember.
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Old 11-01-12, 05:45 AM   #2
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Of course the nut pulls the stem and enhances the seal. All it needs is a gentle twist, not a lot of torque. All presta seals are not made the same, though. Some seal better than others if you leave the nut loose.
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Old 11-01-12, 05:56 AM   #3
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It seals with an o-ring.
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Old 11-01-12, 06:24 AM   #4
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Presta valve nuts are manually operated secondary seals that are not connected to the main valve seal itself. These captive nuts perform the same job as a Schrader valve cap.



Some Schrader valve adapters for Presta valves are known for leaking and, as such, should not be left on the tube. Sometimes your best bet is to carry a Schrader valve adapter with you for "emergency" use with Schrader valve gas station air compressors tire chucks (temporary use of Schrader valve adapters are also often used to check tire pressures if you don't have Presta pressure gauge on hand). However, I recommend that you keep a Presta valve compatible air pump and pressure gauge in your bicycle tool set.
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Old 11-01-12, 07:17 AM   #5
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Originally Posted by FMB42 View Post
Presta valve nuts are manually operated secondary seals that are not connected to the main valve seal itself. These captive nuts perform the same job as a Schrader valve cap...
Totally and unequivocally wrong.
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Old 11-01-12, 07:40 AM   #6
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Here is what I do. Presta has no spring Schrader does and you must tighten the little nut down firm but only finger tight. I use adapters and my pump on the bike is set to Schrader. I leave the adapters on the Presta stem upside down and they act like a cap and protect the stem. I take them off open the stem nut and put the adapter back on with the rubber seal side to the tube. Pump up tire reading pressure on hand pump. When removing there is no chance of letting air out or bending the stem like there is using the Presta head alone. There is one pop of air and that’s the trapped air in the pump. Take off the adapter close the little nut hand tight and reverse the adapter and put it back on the stem till next time. I try and find the aluminum adapters in the fish bowl $1 at my LBS it’s full of about half aluminum half brass. Not that it matters but less weight haha and match my rims main reason.
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Old 11-01-12, 09:51 AM   #7
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Now back home, why not put in another tube with a longer stem?
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Old 11-01-12, 05:08 PM   #8
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Now back home, why not put in another tube with a longer stem?
cause dumb me ordered 4 yes - four 32mm stems
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