Tyre suddenly leaks air at valve. HELP!

Last night I decided to increase the pressure in the tyre a little bit,
so I clamped the pump on and the pumps' own pressure gauge read 37psi as
I expected. I pumped expected to get a target of around 50psi, but once
it got to just about 42psi there was a sudden hissing of air, and within
seconds my tyre had gone completely flat!

I checked the pump was clamped on firmly and pumped it up again from
scratch, and again, and again, and then realised that the valve itself
is leaking. All attempts to reinflate the tyre have been disastrously
unsuccessful, since as soon as the pump is removed all the air escapes
through the valve within seconds.

If I push the valve partially into the tyre while pumping, it will hold
up to about 20psi before starting to leak slowly. Of course as soon as I
release the pressure (i.e. take the pump off) all that air escapes
again.

It is not a tyre puncture, since I can actually feel the air escaping
from the valve itself and the air escapes *in seconds*. The uni has only
ever been ridden indoors,

It is not a fault with the pump, since the valve hissing continues even
*after* I have removed the pump from the valve.

It is a 20x1.95 Maxxis Hookworm tyre that is rated up to 110psi, with a
(leaking) Schrader valve.

So what could it be? And more importantly can I do anything about it? Is
my one month old unicycle already damaged? I can't bear to be without
it!


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gkmac - Shy Nervous Newbie
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the stick in the middle of the valve is like a screw. turn it clockwise
to stop the leak.

Use needlenose pliers, or check the back of the valve cap to see if
there is a slot on the reverse side to use as the unscrewwing tool


--
Sofa - You Tu Tu Tuni?

'You can usually engineer something to be fool proof, but never
damn-fool proof' - cyberbellum
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Sofa wrote:
*the stick in the middle of the valve... *

...is this the stick which lets air out if you push it down?

*is like a screw. turn it clockwise to stop the leak.

Use needlenose pliers... *

...I don't have any needlenose pliers, and being a quarter to midnight
can't get hold of some right now. Of course the stick being totally
round means I cannot shift it with the tweezers.

*...or check the back of the valve cap to see if there is a slot on
the reverse side to use as the unscrewing tool *

Unfortunately there isn't.

If I cannot fix this, is this something that a bike shop would be able
to fix?


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gkmac - Shy Nervous Newbie
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gkmac wrote:
*If I cannot fix this, is this something that a bike shop would be
able to fix? *

Yes, they would be able to fix it. It is not uncommon for the valve
core in a schrader valve to loose air and need to be tightened.

There are automobile valve caps that have a little extension on them for
tightening the valve core.
'valve cap with valve core tool' (http://tinyurl.com/z4mk)
Small needle nose pliers will also work to tighten the valve core.


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john_childs - Guinness Mojo

john_childs (at) hotmail (dot) com
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Thanks for your help people.

The bike shop found that the actual problem was much deeper, in that the
black part of the valve where the valve joins onto the tube was
ruptured. They fitted a new inner tube; problem solved.


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gkmac - Shy Nervous Newbie
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Yes, tubes are cheap. If the problem is only the valve, sometimes it can
be fixed with a little spit!

For this you need a Schraeder valve tool.

Okay, let me back up. What's a Schraeder valve? That's the kind of valve
cars have. If your unicycle or bike has the same valve, with the thingie
in the middle you push down to let the air out, it's a Schraeder. These
are not the best valves for cycling, for several reasons, but they are
very common in the States.

The Schraeder valve's insides can be unscrewed. I never tried a
needlenose pliers, but that might work. Better to use a valve tool. It
fits over part of the inside of the valve, and then you can unscrew it.
As John Childs mentioned, sometimes these are built into the heads of
metal valve caps. It looks like a little piece of tube with a slot cut
in the end.

If your tire is leaking at the valve, and you've determined the problem
is in the valve and not a leak just next to it (new tube needed then),
take out the valve and spit on it. This is a common technique for
mechanics, car and bike. Get some saliva on there, on the seal, then put
the valve back in. This often fixes the problem and off you go!

If your tire continues to leak from the valve, I suppose you could try a
new valve in the same tube. Otherwise, it's time for a new tube. Tubes
are cheap, especially when you're not 5 miles from the car, on a
mountain trail!


--
johnfoss - IUF Director

John Foss, the Uni-Cyclone
"jfoss" at "unicycling.com"
www.unicycling.com

"My sister wanted to buy the new Eminem CD. I had to say to her, 'Like,
you can't hear it.'" — my nephew Austin Miller, whose sister Alexa is
100% deaf... But she can ride a unicycle!

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