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valve and pressure question

Started by Mark Shaw · · Last activity · 7 posts · 261 views

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01 / Original postvalve and pressure questionMark Shaw · 8 Apr 2005 02 / This pagePosts 1–7Page 1 of 1 · chronological order 03 / Latest replyPost #7Bob Anderson · 11 Apr 2005

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Road Cycling
Published
8 April 2005
Last activity
11 April 2005
Original author
Mark Shaw
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7
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Public discussion
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  1. Original post
    Mark Shaw
    Archived post
    #1

    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. David L. Johnson
    Archived post
    #2
    Mark Shaw said:

    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

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  3. Leo Lichtman
    Archived post
    #3

    "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.

    Report
  4. Maggie
    Archived post
    #4
    Leo Lichtman said:

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


    defective,

    Quoted message said:

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


    a

    Quoted message said:

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


    the

    Quoted message said:

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


    you

    Quoted message said:

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


    It could

    Quoted message said:

    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

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  5. Mark Shaw
    Archived post
    #5
    Leo Lichtman said:

    "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

    Report
  6. Mark Shaw
    Archived post
    #6
    Mark Shaw said:

    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.

    Quoted message said:

    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

    Report
  7. Bob Anderson
    Archived post
    #7
    Mark Shaw said:

    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

    Report

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