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presta valve screws out



 
 
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  #1  
Old September 12th 04, 02:44 PM
Paul Nevai
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Default presta valve screws out

Another day, another surprise. I found out that the presta valve on one of my
tubes screws out. In fact, it screws out and the tube loses pressure
appr. one out of ten times when I screw of the little plastic valve cap from
it. I never knew that those cores can be screwed out and it appears that on
all but one of my tubes it can't be screwed out, and are in fact not even
separate pieces but are part of the valve stem.

Let me try to specify. It's not the "core" what screws out but the thing
which holds the core and which itself is screwed into the valve stem.

So when this thingie can be screwed out, is this a "lower" or "higher"
quality indicator.

Also, how can I screw it in so it would never ever screw out again, I tried
to wrap a rubber piece around it and then use a wise grip plier but I am not
sure it worked.

Thanks, Paul
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  #2  
Old September 12th 04, 02:52 PM
psycholist
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Default


"Paul Nevai" wrote in message
...
Another day, another surprise. I found out that the presta valve on one of

my
tubes screws out. In fact, it screws out and the tube loses pressure
appr. one out of ten times when I screw of the little plastic valve cap

from
it. I never knew that those cores can be screwed out and it appears that

on
all but one of my tubes it can't be screwed out, and are in fact not even
separate pieces but are part of the valve stem.

Let me try to specify. It's not the "core" what screws out but the thing
which holds the core and which itself is screwed into the valve stem.

So when this thingie can be screwed out, is this a "lower" or "higher"
quality indicator.

Also, how can I screw it in so it would never ever screw out again, I

tried
to wrap a rubber piece around it and then use a wise grip plier but I am

not
sure it worked.

Thanks, Paul


I don't have any answers for you, but I share your frustration. I don't
know why some are made this way and some aren't. I suspect Jobst will chime
in and clarify this. Anyway, bonehead me left on a long ride a few weeks
back and had only one CO2 cartridge in my seat bag. I got a flat. I
changed it out. My wheels have deepish, semi-aero rims and I have to use a
valve extender to pump them up. So I've used my last CO2 cartridge to fill
the repaired tire and I go to remove the valve extender. The core of the
new tube unscrews with the valve extender and there I am ... stranded. I
live in a very rural area. I had a very long walk to get to where I had a
cell phone signal to be able to call home. I spent a lot of that time
wondering what possible reason there could be for the core of a valve to
unscrew like that. Never came up with one.

Bob C.


  #3  
Old September 12th 04, 03:23 PM
mark
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Posts: n/a
Default


"Paul Nevai" wrote ...
Another day, another surprise. I found out that the presta valve on one of

my
tubes screws out. In fact, it screws out and the tube loses pressure
appr. one out of ten times when I screw of the little plastic valve cap

from
it. I never knew that those cores can be screwed out and it appears that

on
all but one of my tubes it can't be screwed out, and are in fact not even
separate pieces but are part of the valve stem.


I discovered the same thing about a spare tube I was installing the other
day. The tube had an extra long valve stem to fit an aero or semi-aero rim.
I suspect that the removable valve lets the manufacturer install valves in
stems of varying lengths, according to consumer demand.


So when this thingie can be screwed out, is this a "lower" or "higher"
quality indicator.


Mine seems to be about the same quality as the valves on the other tubes I
buy.

Also, how can I screw it in so it would never ever screw out again, I

tried
to wrap a rubber piece around it and then use a wise grip plier but I am

not
sure it worked.


I suspect that this would distort the valve or strip the threads, making the
whole thing useless. I got mine as tight as I could with my fingers, left it
at that, and made a note not to buy that brand of tube again.
--
mark


  #4  
Old September 12th 04, 04:22 PM
david
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Default

I believe the reason is, if you bend the valve, you can replace it. As for
tubulars, you can unscrew the valve, install an extension, and then screw
the valve into the extension piece. It makes for a far far better seal then
using the valve extenders that screw on over the valve fitting. Its a great
feature.

David


  #6  
Old September 12th 04, 06:44 PM
psycholist
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Posts: n/a
Default


wrote in message
...
On 12 Sep 2004 13:44:43 GMT, (Paul
Nevai) wrote:

Another day, another surprise. I found out that the presta valve on one

of my
tubes screws out. In fact, it screws out and the tube loses pressure
appr. one out of ten times when I screw of the little plastic valve cap

from
it. I never knew that those cores can be screwed out and it appears that

on
all but one of my tubes it can't be screwed out, and are in fact not even
separate pieces but are part of the valve stem.

Let me try to specify. It's not the "core" what screws out but the thing
which holds the core and which itself is screwed into the valve stem.

So when this thingie can be screwed out, is this a "lower" or "higher"
quality indicator.

Also, how can I screw it in so it would never ever screw out again, I

tried
to wrap a rubber piece around it and then use a wise grip plier but I am

not
sure it worked.

Thanks, Paul


Dear Paul,

Sealant tubes use this design to allow pumping goo into the
tube.

If you're screwing a plastic cap onto a Presta valve so hard
that it unscrews a metal fitting, you may be using
considerablly more force than necessary.

I'm not recommending a torque wrench for valve caps, but
using two fingers and a lighter grip may help.

Carl Fogel


Carl,

If you've ever used a valve extender, you know that you sometimes have to
screw them on pretty tightly to avoid having more of the air you pump in
exit via the threads instead of going into the tube. It can be a real trick
to screw them on tight enough for inflation, but loose enough that they can
be removed without coring the valve.

FYI,
Bob C.


  #7  
Old September 12th 04, 07:12 PM
[email protected]
external usenet poster
 
Posts: n/a
Default

On Sun, 12 Sep 2004 13:44:10 -0400, "psycholist"
wrote:


wrote in message
.. .
On 12 Sep 2004 13:44:43 GMT, (Paul
Nevai) wrote:

Another day, another surprise. I found out that the presta valve on one

of my
tubes screws out. In fact, it screws out and the tube loses pressure
appr. one out of ten times when I screw of the little plastic valve cap

from
it. I never knew that those cores can be screwed out and it appears that

on
all but one of my tubes it can't be screwed out, and are in fact not even
separate pieces but are part of the valve stem.

Let me try to specify. It's not the "core" what screws out but the thing
which holds the core and which itself is screwed into the valve stem.

So when this thingie can be screwed out, is this a "lower" or "higher"
quality indicator.

Also, how can I screw it in so it would never ever screw out again, I

tried
to wrap a rubber piece around it and then use a wise grip plier but I am

not
sure it worked.

Thanks, Paul


Dear Paul,

Sealant tubes use this design to allow pumping goo into the
tube.

If you're screwing a plastic cap onto a Presta valve so hard
that it unscrews a metal fitting, you may be using
considerablly more force than necessary.

I'm not recommending a torque wrench for valve caps, but
using two fingers and a lighter grip may help.

Carl Fogel


Carl,

If you've ever used a valve extender, you know that you sometimes have to
screw them on pretty tightly to avoid having more of the air you pump in
exit via the threads instead of going into the tube. It can be a real trick
to screw them on tight enough for inflation, but loose enough that they can
be removed without coring the valve.

FYI,
Bob C.


Dear Bob,

True, but the original post specifically complains about
plastic valve caps, not extenders.

As for valve extenders, I found them so annoying that I
switched to long valve stems after fooling around with
teflon tape to seal the threads.

Another problem is that the extender is just a hollow shell
that fits down over the real Presta valve, whose lock-nut
must be left unscrewed, leaving nothing but air-pressure to
seal the valve.

In addition to the obvious problem of losing air-pressure
without a lock-nut, the extender makes it hard to break a
stuck valve free.

This can cause two problems. First, you can't pump the tube
any further if the valve sticks on a mostly-filled tube.
Second, you can't let the air out to collapse a slow-leak
flat to remove the tire.

So you have to remove and replace the extender, an awkward
job, or else carry something to poke down into it to free
the hidden Presta valve.

In general, most small adaptors, extenders, and adjustable
devices fail to work as well as the real things whose
specific purpose they are meant to imitate.

Carl Fogel
  #8  
Old September 12th 04, 09:59 PM
Chuck Davis
external usenet poster
 
Posts: n/a
Default


wrote in message
...
.....
As for valve extenders, I found them so annoying that I
switched to long valve stems after fooling around with
teflon tape to seal the threads.

Another problem is that the extender is just a hollow shell
that fits down over the real Presta valve, whose lock-nut
must be left unscrewed, leaving nothing but air-pressure to
seal the valve.

In addition to the obvious problem of losing air-pressure
without a lock-nut, the extender makes it hard to break a
stuck valve free.

This can cause two problems. First, you can't pump the tube
any further if the valve sticks on a mostly-filled tube.
Second, you can't let the air out to collapse a slow-leak
flat to remove the tire.

So you have to remove and replace the extender, an awkward
job, or else carry something to poke down into it to free
the hidden Presta valve.

In general, most small adaptors, extenders, and adjustable
devices fail to work as well as the real things whose
specific purpose they are meant to imitate.

Carl Fogel


If you use an extender such as:

http://www.worldclasscycles.com/valv...nsion_tube.htm

you'll find that they have a valve control that allows you to open and close
the valve. The metal extenders do need an O-ring or Teflon tape for a good
seal on the valve, but plastic versions of this type of extender will seal
as is.

Chuck Davis


  #9  
Old September 12th 04, 10:44 PM
Paul Kopit
external usenet poster
 
Posts: n/a
Default

On Sun, 12 Sep 2004 13:44:10 -0400, "psycholist"
wrote:

If you've ever used a valve extender, you know that you sometimes have to
screw them on pretty tightly to avoid having more of the air you pump in
exit via the threads instead of going into the tube. It can be a real trick
to screw them on tight enough for inflation, but loose enough that they can
be removed without coring the valve.


If you put some teflon tape on the valve stem, the extenders work
fine. You can also put a piece of teflon into your patch kit.
 




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