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So I have just semi retired my 2009 Stumpy and bought a new bike with 650b tubeless wheels which seem to be a big improvement. However while out at Greno woods this morning thought I may need some more air in rear tyre so attached my Lezyne pump with the flex hose and put a couple of PSI of air into tyre. Undid the pump at which point all the air came out of my valve! I took a look and the valve core had come undone and was still attached to the pump hose - never-mind put it back in the valve and try again. Same thing happens so tried again but with the hose not so tight and only put a few pounds in and took pump off for a test all fine so ensured core was tight and attached hose and pumped to desired pressure. Yep you guessed it undid the hose AHHH all the bloody air comes out with core firmly attached to the hose - so am I being dumb, incompetent or do I just need to MTFU and not use a screw on hose pump?
Clip on pump might be better, athlough of you not the sort that needs to remove valve cores, thread lock or glue it in. And when you next replace the tube, you can get them with non removable cores.
Thanks I thought that may be the answer, i forgot to say I was running tubeless!
Those pumps are notorious for doing that, I've had the same experience and also broken a tubeless valve (never get alu valves) with it. If you press the pressure release button on the hose it can help but not always. Best thing is to make sure the core is nipped up tight enough.
Yep they may not be tight enough, they are new so may just need some tinkering
Just read on Lezyene website "Â on presta valves with a removable valve core: Before use with pump, remove valve core and apply small amout of LOCTITE thread locker to valve core threads. Reinstall valve core and securely tighten" teach me not to RTFM!
Yeh I had it once with a conti tube, sometimes they are just a bit loose when new and need a good nip up.
also, they heat up with air being pumped in... had it happen to me before and i pumped up the tyre, then sat about for 5 mins whilst it cooled down, then unscrewed the hose.... a faff
Had this problem too. Solved it by accident. Use a valve extender like you need for deep aero rims. Keep this screwed into the hose and just screw that on instead. Can keep it permanently attached as there's enough room in the pump barrel once you put the hose away.
Newer ones have a button on the hose to release the pressure. Pressing this before unscrewing greatly reduces the chance of the core coming out.
I've also noticed on mine that the grommet  still grips the valve core after the thread is disengaged. This can be enough to unscrew the core.
I think what I'm saying is, tightening the core will help.
Great tip Clubby. Ta 🙂
It is slightly annoying, but you don't need to do it up that tight you need loctite on valve core!?
What annoys me more about the Lezyne is that it screws onto the core in the first place. WTF not screw onto the body so I can pump it up without the core in for seating? FFS!
Anyone know of a converter so you can attach the Lezyne head to a coreless valve? Or just find a replacement head from some other manufacturer?
Clubby you sir are a genius! Valve extender ordered, delivered and does the job! thanks again