nesdog

Had a rear flat yesterday. After inflating the replacement tube nicely, I unscrewed the hose from the pump and the top of the valve unscrewed out of the stem with it. Psssst.....Ah, nuts. Took me several attempts to get it to stay on and I had to limp home with a partially filled tire.

Once home, I took a pliers and tightened the top down. Haven't had this occur before so I'm wondering if I should be concerned that the top will blow off at some point and should just replace the tube now.

bikepro

The problem was simply due to the valve not being tight in the stem. It happens. Check that the valves in your spare tubes are tight and go on.

rpeterson

Yup, just something that happens sometimes. Tighten it down and don't worry about it.

xjustice09x

If you dont want that to happen buy tubes without a removable core.

That happened to me before when I bought some continental tubes which I didnt realize had removable cores. Newer lezyne pumps have a air bleed system that lets you release the pressure in the hose by pressing a button before unscrewing the hose from the valve. That helps prevent the presta core from unthreading.

B. Carfree

And yet the Lezyne pump that arrived last week came with instructions to use Loc-tite on removable cores to prevent them from coming out when the pump head is removed.

rpeterson

Bleeding can help prevent it, but that's not its main purpose and with a screw on pump loctite is probably a good idea.

Bah Humbug

Happens to me periodically with Continental tubes. I think it's responsible for my one race flat.

nesdog

Thanks for the feedback. Also using Conti tubes and a Lezyne mini pump...no bleed setting though that I'm aware of.

Nachoman

It's happened to me too. And it was quite annoying.

MikeyBoyAz

I stopped using pumps... uhh, at all... I use a N2 tank with a cnc'd presta head inflator; It's pretty awesome. Only costs $37 to fill a 125cf tank once a year... While on the road I make sure I have 1 more CO2 than I have tubes and a cell phone for when/if the second tube goes down. I also make it a point to not ride so far out into nowhere that I don't have signal.

On topic... I had a Lyzne pump and it did what the OP described; it was annoying. I made sure I tightened down the valves on my tubes before I installed them, once I did that I didn't experience that issue anymore; a spritz of compressed PTFE spray also made it that much easier to remove under pressure, and though I had to reapply now and again, it was worth it for the easy operation.

StanSeven

Lezyne floor pumps are the textbook example of a solution looking for a problem. The screw off head is a good idea for a mini pump but doesn't make sense for a floor pump at all. I returned mine and a got a really solid one from Giant with the standard lever that works so much better - and doesn't pull the core out.

And Lezyne's solution to having to put locktite on cores is ridiculous. Anyone that thinks that makes sense is so brand loyal you aren't being objective.

topflightpro

I don't entirely disagree with this statement. That said, I have found the screw on Lezyne to be the among the easier and more effective pump heads to use. (I also have a Silca and Park pump in my garage.) The biggest problem with the Lezyne design is that it doesn't work with valve extenders.

Bah Humbug

My Conti valve cores, by the way, sometimes loosen from floor pumps; it isn't only from the Lezyne screw-on types.

Smiziley

I have a Lezyne pump too and it happens occassionally. It's just annoying, as the threaded head chuck is threading onto the valve core instead of the valve stem. I find it helps to have a small wrench, or needle nose pliers handy to tighten the core in this situation. Bleeding does nothing except remove the pressurized air from the tube.

What causes the valve core to unseat from the stem is that you're putting the head chuck on at a slight angle, and it needs to go on straight. I find that rotating the wheel 90* or so and being careful to thread the head chuck straight on helps prevent the valve core from unthreading.