presta valves

rowman

I've been having an issue with presta valves since I purchased a new zefal track pump. After topping up the pressure a few times the valve initially starts to leak air when I unscrew the top nut. Eventually the valve blows out of the body? Anyone any ideas what’s going on?

Wooliferkins

Blows out or unscrews?

keef66

Does the pump connector screw on to the valve? If so I suspect you're unscrewing the valve core a bit each time you remove it.

You can get tubes with cores that can't be unscrewed.

dabber

I've had problems with my conti inner valve core unscrewing when reinflating out on the road after punctures. This has been when using my Lenzyne Pressure Drive pump which has a screw on hose.
As I've got a few new conti inners and I never wanted to chuck them and replace them with inners with non removable cores I tried to find a solution. What seems to have worked is to take the cores out and wrap around the thread a thin layer of ptfe plumbers tape.

Reading inner tubes descriptions I've found it generally unclear as to which have removable cores and those that don't.

Mike67

I've had the same happen with a Conti innner tube 5mins before that start of a cross race whilst letting a bit of air out. Seems to be a compulsory activity on the start line
Not fun :evil:

Undoing the top nut also unscrewed the core with the inevitable results. Seems to be an issue with all my conti inner tubes.

I didn't go as far as ptfe tape but undid the top nut and applied a thin spanner to the flats on the valve core whilst gripping the valve stem and nipped them up. Also put a touch of GT85 on the top nut to give it less stiction than the core itself.

Seems to have worked so far.

rowman

They are indeed conti tubes. I'll try retightening the valve core? Thanks.

Wooliferkins

I had the same Lezyne/Conti valve malarkey. Light touch of threadlock carefully applied and judicious use of a valve core spanner. Problem sorted.

sungod

conti ships tubes with the valves loose

use pliers or a valve core tool, make the valves *tight*, then they won't come undone, get the habit of doing it to new tubes when you first get them

i use a lezyne screw-on hand pump, i've never had a core come loose once i've tightened it

also, when you screw on the pump hose, you don't need to do it up tight, only just enough to prevent leakage - there's a rubber seal inside the pump head - so start gently, as the pressure goes up if it starts to leak then just give it another half-turn

dabber

sungod wrote:

conti ships tubes with the valves loose

use pliers or a valve core tool, make the valves *tight*, then they won't come undone, get the habit of doing it to new tubes when you first get them

i use a lezyne screw-on hand pump, i've never had a core come loose once i've tightened it

also, when you screw on the pump hose, you don't need to do it up tight, only just enough to prevent leakage - there's a rubber seal inside the pump head - so start gently, as the pressure goes up if it starts to leak then just give it another half-turn

I did pre-tighten them as you suggest but it never made any difference for me. I do agree about not overtightening the the hose to the valve. This problem is an irritation when you've just had your ride disrupted by a puncture, think you've fixed and then have to start fuffing around with the valve.