That's unfortunate. But that's not my experience.

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Swim. Overbike. Walk.

To provide some balance I have experienced the same failure you are describing on 2 or 3 of these extenders so yes they do break. However they aren't/weren't designed to be like traditional valve extenders and are brilliant when used as designed. For the price I think they last long enough that I have no problem recommending them.

The extenders are designed to get you out of a tough bind i.e. I have a flat and **** the valve stems I brought don't fit the wheel. Twice on club rides they saved the day when someone flatted only to realize that they didn't have the right tubes but as I could readily lend then the extenders it wasn't an issue. Similarly come race day these can be packed very easily along with the spare replacement kit and deployed rapidly rather than having to store a tube with a pre-attached long valve extender. [I have damage valve stems trying to manipulate them and the extenders into place for packing so pre-attaching extenders is not without some risk].

If you need something for day to day use, which you would with latex tubes, they are not the right solution. Specifically they should not be left onto the original valve stems because the metal of the stems will expand/contract with temperature differently to the plastic of the extender and help the rubber bit break free. But what they lack in durability they make up for in being able to get you out of a tough situation.

For my first IM, I used these on tubular tires. When I was pumping up my tires a few minutes before the start and I pulled the pump head off the valve, the Topeak extender came right off with it.

I froze for a moment mortified - 10 minutes to go, my very first IM, all that training and I was about to get a flat in transition with glue-on tires

But of course it didn't go flat. The normal valve below was held tight by the force of the air. Rode the whole IM that way, worrying all the time. It turned out OK, but I've never used the Topeaks since.

Not my experience either. I use this on my Hed Jet 9 front wheel and have kept it on there for >2yrs without problem. It is only providing the seal when you inflate, because you keep the original valve core and this has a knurled thingybob that allows you to open and close the valve head through the extender.

If it helps any, I wrapped the threaded part of the valve I attach this to with PTFE tape. I never take the thing off, and I'm using it pretty often because of latex tubes (albeit on my race bike which generally lives on the turbo).

I think one trick, aside from the plumbers tape, is to not try and tighten the valve nut too much when you've finished pumping. I can see how this would eventually strip the knurls on the valve nut. There isn't much need, the valve is kept closed by air pressure anyway.. just tighten it up enough to reduce the risk of it being pressed in somehow.

Perhaps it's luck. Perhaps its manufacturing defect. Perhaps it's just user error. In any case, for me - it was probably due to a mixture of user error and an inherent design problem with it.

User Error in that I didn't know what was the protocol w these extenders. My initial extender (from the bike shop) told me that the ones w/ the removable cores are better and are meant to stay in place and not be taken out. But since my latex tubes weren't with removable valve cores, I had to return the removable valve core extenders and find another retailer. (the other retailer didn't provide any helpful hints and thus I just used it like the removable valve core extenders)

I have now kept the remaining one (which I fixed using some Glue and just glued the 2 pieces back together) in the saddle bag.

I hope that the silca extenders would be better. and I think it's supposed to be left there

https://silca.cc/...or-all-presta-valves

I tried PTFE tape too, but it ended up being too fat and can't go into the rim hole. That could also have expanded the extenders which made things worst.

As a word of warning I would be careful about the one you fixed with glue. I have tried it before and it failed extremely quickly when I tried to use it.

Thanks for the warning. As a matter of fact, it failed spectacularly after I glued it and tried to use it> (although I didn't wait that long for the glue to set).
In any case, It will have to do for now until my new ones comes. Right now, they are all I have.