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valve and pressure question



 
 
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  #1  
Old April 8th 05, 03:24 PM
Mark Shaw
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Default valve and pressure question

I'm a newbie. I haven't seriously ridden bicycles since I was
in high school, which was thirty years ago. Recently I bought a
nice used Cannondale, and am still getting back into it. So
bear with me, if you will.

I bought a floor pump (Blackburn Airtower 4) fitted with two
terminals, one for Shrader valves and the other for Prestas. I
have Prestas. The pump also has a pressure gauge.

My tires are rated for 80psi. If I pump them to that pressure
by the pump's gauge, and then check with a handheld digital gauge
and a Shrader/Presta adapter, they show about 56psi. If I then
leave the adapter on the valve stem and attach the pump via the
Shrader side of the hose, I also see 56psi. So I pump it up to
80, and check again with the handheld gauge. Dead on.

So I'm seeing two different pressure readings, depending on the
presence of the adapter and which terminus of the pump I'm using.

The tires feel like the readings with the adapter are probably
right, based on my thirty-year-old experience. So I'm probably
going to just continue using it, unless somene raises a red
flag.

I'm curious about what might be going on here, though. Could
the adapter possibly make that much difference?

Thanks.

--
Mark Shaw moc TOD liamg TA wahsnm
================================================== ======================
"All of my mistakes are giving me ideas." - Natalie Lileks
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  #2  
Old April 8th 05, 03:43 PM
David L. Johnson
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On Fri, 08 Apr 2005 14:24:15 +0000, Mark Shaw wrote:

So I'm seeing two different pressure readings, depending on the
presence of the adapter and which terminus of the pump I'm using.


I take it the pump is one of those double-headed jobs, with Shader on one
side of the head, Presta on the other.

The air pressure is read, though, back at the pump body, so it should not
even know what end is used. Something is wrong.

Chances are that the separate pressure gauge is correct. Take your pump
back to the shop where you got it and explain your situation. I guess the
pump is somehow defective, with some blockage in the presta side of the
head.

--

David L. Johnson

__o | "A foolish consistency is the hobgoblin of little minds, adored
_`\(,_ | by little statesmen and philosophers and divines." --Ralph Waldo
(_)/ (_) | Emerson


  #3  
Old April 8th 05, 05:16 PM
Leo Lichtman
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"David L. Johnson" wrote: (clip) I guess the pump is somehow defective,
with some blockage in the presta side of the head.
^^^^^^^^^^^^^^
If you operate the pump with the Presta setting, but not connected to a
valve, does it register any pressure on the gauge? Compare this to the
Shraeder setting. Is there a difference? On the Presta setting can you
compress air, so you have a gauge reading that does not bleed off? It could
be that there is a scrap of rubber in the valve that is blocking air flow.


  #4  
Old April 8th 05, 05:51 PM
Maggie
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Default


Leo Lichtman wrote:
"David L. Johnson" wrote: (clip) I guess the pump is somehow

defective,
with some blockage in the presta side of the head.
^^^^^^^^^^^^^^
If you operate the pump with the Presta setting, but not connected to

a
valve, does it register any pressure on the gauge? Compare this to

the
Shraeder setting. Is there a difference? On the Presta setting can

you
compress air, so you have a gauge reading that does not bleed off?

It could
be that there is a scrap of rubber in the valve that is blocking air

flow.


I think I will give some advice on this one....ummmmm......maybe not.
TGIF.
Maggie

  #5  
Old April 8th 05, 08:24 PM
Mark Shaw
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Default

Leo Lichtman wrote:

"David L. Johnson" wrote: (clip) I guess the pump is somehow defective,
with some blockage in the presta side of the head.
^^^^^^^^^^^^^^
If you operate the pump with the Presta setting, but not connected to a
valve, does it register any pressure on the gauge? Compare this to the
Shraeder setting. Is there a difference? On the Presta setting can you
compress air, so you have a gauge reading that does not bleed off? It could
be that there is a scrap of rubber in the valve that is blocking air flow.


There's no "setting" per se, just two holes in the chuck end of the
hose - one for Presta, the other for Schrader. They both seem to be
able to hold compressing air pretty well.

I'll just take it back to the shop and ask them to check it out. It
could very well be that I'm not using it correctly.

--
Mark Shaw moc TOD liamg TA wahsnm
================================================== ======================
"All of my mistakes are giving me ideas." - Natalie Lileks
  #6  
Old April 9th 05, 12:09 AM
Mark Shaw
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Default

Mark Shaw wrote:
There's no "setting" per se, just two holes in the chuck end of the
hose - one for Presta, the other for Schrader. They both seem to be
able to hold compressing air pretty well.


I'll just take it back to the shop and ask them to check it out. It
could very well be that I'm not using it correctly.


Well, I took it in. And the tech demostrated it working perfectly
on their bike. So I don't know what's up.

I'll continue playing with it; maybe I released too much air. The
Presta valve is a new thing to me....

Thanks for all the help.

--
Mark Shaw moc TOD liamg TA wahsnm
================================================== ======================
"All of my mistakes are giving me ideas." - Natalie Lileks
  #7  
Old April 11th 05, 02:13 AM
Bob Anderson
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Default

On Fri, 8 Apr 2005 14:24:15 +0000 (UTC), Mark Shaw
wrote:

I'm a newbie. I haven't seriously ridden bicycles since I was
in high school, which was thirty years ago. Recently I bought a
nice used Cannondale, and am still getting back into it. So
bear with me, if you will.


Right on, good move. Enjoy the riding, welcome to the group.


---
"BitwiseBob" - Bob Anderson
Eugene Oregon
 




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