what's it for?

[buggi]

Today, i broke the presta valve on my inner tube when pumping it up. i yanked the pump off (at an awkward angle) and it broke at the base.

what i mean by "at the base" is that the twisty thing that sits on the thin bit of metal (the bit you have to undo), along with the thin bit of metal that you push in to release the air, broke off, leaving only the fat bit behind and part of the thin bit still inside the fat bit but now both are the same level. (still with me?... well, i don't know how else to explain it)

but then i noticed that this didn't make any difference at all.
my tyre didn't go down and i can even pump it up still, because when i put my pump on it still pushes the thin bit in (the bit that is left). so i just put the cap back on.

so it got me wondering. why do they bother to put the twisty thing on in the first place? why not just level the fat bit and the thin bit off the same, and put the cap on it?

 

[Mr Pig]

the twisty thing on the thin bit , along with the thin bit, broke off, leaving the fat bit and part of the thin bit inside the fat bit but now both are the same level.

I know what you mean and it still hurts my head! ;0)

 

[Hover Fly]

Because vibrations can shake the thin bit loose so it falls back into the big rubbery bit and all that invisible stuff you pushed in with that thing you push on goes out again.

 

[bonj2]

show pics.

but trying to pump it up when the valve is not unscrewed correctly will bork the valve, as it will lose its ability to spring out and thus hold the air in when its unscrewed - I did this on the last sportive, fortunately it held enough air to get me to the feed station where i borrowed a pump

 

[Gerry Attrick]

Because at high speed, centrifugal force can cause a major immediate deflation. Replace your tube now, immediately, straight away, don't wait.

 

[buggi]

Because at high speed, centrifugal force can cause a major immediate deflation. Replace your tube now, immediately, straight away, don't wait.

Really? o bollocks, that actually makes sense. you mean the high speed pressure might force the thin bit out? no that doesn't make sense after all coz the twisty thing stops it from going in only.

 

[fossyant]

Erm, that's the 'top' of the valve....the little lock nut, that stops the valve from being pressed in.... I'd replace it....i.e new tube.....

The valve is unlikely to get depressed (sob.....) but over tightening of the valve dust cover can cause loss of pressure..... and the lock nut ensures the valve sits tight and 'square'.

 

[fossyant]

Buggi...Gerry is in the wind up......... just get another as you risk failure due to the valve potentially not sitting straight with a dust cap fitted.....

 

[Gerry Attrick]

Buggi...Gerry is in the wind up......... just get another as you risk failure due to the valve potentially not sitting straight with a dust cap fitted.....

Sorry Fossy. No wind up. It has happened in the past. Why have the locknut if it is not needed?

 

[buggi]

Gerry you are winding me up? the locknut is to stop the thin bit getting depressed accidently it doesn't stop it from being pulled out does it? the whole thing has thin bit snapped off, not just the locknut, so as it's now level with the wide bit, the dust cap won't effect it will it? i've only got one spare on me, which means if i replace it now i go out tomorrow with no spare.

 

[Gerry Attrick]

The air is released when the the unscrewed "thin bit" is pressed, right? If you can press the unscrewed "thin bit", then centrifugal force certainly can. That is the reason Presta valves were designed.

 

[buggi]

The air is released when the the unscrewed "thin bit" is pressed, right? If you can press the unscrewed "thin bit", then centrifugal force certainly can. That is the reason Presta valves were designed.

o right, yea that kind of make sense. like being on a spinny thing at the fair and behind forced into your seat?

so why haven't the other type of valve got a locknut? because now my valve just looked like the other type of valve.

 

[Radius]

Erm, if you've broken the important part of the valve off, I shouldn't think using it is a very good idea...Gerry's not joking this time!

 

[Gerry Attrick]

Because the Schrader valve has a spring to keep the valve closed. The Presta valve relies on the screwed collar.

 

[longers]

Because the Schrader valve has a spring to keep the valve closed. The Presta valve relies on the crewed collar.

He's right. Wiki says so