Silca pump gauge failed after reassembly?

Discussion in 'Cycling Equipment' started by Michael, Mar 15, 2003.

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  1. Michael

    Michael Guest

    When I needed to replace the rubber gasket in the pump head of my Silca Super Pista, I took the
    opportunity to take the pump completely apart and re-lube everything. But after I put it all back
    together, the gauge stopped working.

    On the push stroke the needle goes to approximately the right pressure reading, but immediately
    falls back to 0. The pump works fine - I can verify the pressure with a separate guauge I've got -
    but previously the needle would hold at the current pressure as I pumped. It's pretty hard to read
    the value now in the split second the needle peaks at a number, especially considering how close
    together the gauge ticks are.

    I can't believe I broke the gauge just by taking it off and putting it back on. There's no magic to
    how it attaches - it's compressed between the foot pedal and the pump body via 2 bolts, and the
    intake hole lines up with a hole at the bottom center of the pump body.

    Any ideas?
     
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  2. On Sat, 15 Mar 2003 19:12:29 -0800, Michael wrote:

    [snip]
    > On the push stroke the needle goes to approximately the right pressure reading, but immediately
    > falls back to 0. The pump works fine - I can verify the pressure with a separate guauge I've got -
    > but previously the needle would hold at the current pressure as I pumped. It's pretty hard to read
    > the value now in the split second the needle peaks at a number, especially considering how close
    > together the gauge ticks are.

    This sounds to me like a problem with a one way valve someplace. Since the pump works, I'd have to
    guess that the guage is just on the "wrong side" of the valve, or if it's set up to "pass through",
    then that one of two valves is missing. Greg
     
  3. Mark Boyd

    Mark Boyd Guest

    On Sat, 15 Mar 2003, Michael wrote:

    > When I needed to replace the rubber gasket in the pump head of my Silca Super Pista, I took the
    > opportunity to take the pump completely apart and re-lube everything. But after I put it all back
    > together, the gauge stopped working.
    >
    > On the push stroke the needle goes to approximately the right pressure reading, but immediately
    > falls back to 0. The pump works fine - I can verify the pressure with a separate guauge I've got -
    > but previously the needle would hold at the current pressure as I pumped. It's pretty hard to read
    > the value now in the split second the needle peaks at a number, especially considering how close
    > together the gauge ticks are.
    >
    > I can't believe I broke the gauge just by taking it off and putting it back on. There's no magic
    > to how it attaches - it's compressed between the foot pedal and the pump body via 2 bolts, and the
    > intake hole lines up with a hole at the bottom center of the pump body.
    >
    > Any ideas?
    >
    Yep. You didn't get the check valve back in there properly. The gauge is between the check valve and
    the tire's valve. If the tube uses a presta valve, that alos acts a check valve that keeps the air
    in the tire from coming out when you release the pressure in the pump barrel. Normally the check
    valve at the bottom of the pump barrel keeps the air in the gauge and hose from flowing back into
    the pump so that the gauge holds its reading between pump strokes.

    Think about the burst of air you hear when you remove the chuck from the stem. That is the air
    between the pump's check valve and the tire's "check valve" rushing out. That is also the air whose
    pressure is read by the pump's gauge. When the check valve in the pump isn't working, that air flows
    back into the pump each time you complete a pump stroke. You can still pump a presta valved tire up,
    but the gauge will behave as you have described.

    Mark <www.cs.unca.edu/~boyd/bicycling.html
     
  4. Tim McNamara

    Tim McNamara Guest

    In article <[email protected]>, [email protected]
    (Michael) wrote:

    > When I needed to replace the rubber gasket in the pump head of my Silca Super Pista, I took the
    > opportunity to take the pump completely apart and re-lube everything. But after I put it all back
    > together, the gauge stopped working.
    >
    > On the push stroke the needle goes to approximately the right pressure reading, but immediately
    > falls back to 0. The pump works fine - I can verify the pressure with a separate guauge I've got -
    > but previously the needle would hold at the current pressure as I pumped. It's pretty hard to read
    > the value now in the split second the needle peaks at a number, especially considering how close
    > together the gauge ticks are.
    >
    > I can't believe I broke the gauge just by taking it off and putting it back on. There's no magic
    > to how it attaches - it's compressed between the foot pedal and the pump body via 2 bolts, and the
    > intake hole lines up with a hole at the bottom center of the pump body.

    No, you've just got a pressure leak somewhere. Check all the connections- the valve chuck, the
    connections to the hose, and the connection between the gauge and the pump body. You could submerge
    the bottom 1/3 of the pump and try pumping a tire- that would rule
    in/out most of the possibilities. If it passes this check, then recheck the chuck, hose connection,
    and leather piston.
     
  5. A Muzi

    A Muzi Guest

    "Michael" <[email protected]> wrote in message
    news:[email protected]...
    > When I needed to replace the rubber gasket in the pump head of my Silca Super Pista, I took the
    > opportunity to take the pump completely apart and re-lube everything. But after I put it all back
    > together, the gauge stopped working.
    >
    > On the push stroke the needle goes to approximately the right pressure reading, but immediately
    > falls back to 0. The pump works fine - I can verify the pressure with a separate guauge I've got -
    > but previously the needle would hold at the current pressure as I pumped. It's pretty hard to read
    > the value now in the split second the needle peaks at a number, especially considering how close
    > together the gauge ticks are.
    >
    > I can't believe I broke the gauge just by taking it off and putting it back on. There's no magic
    > to how it attaches - it's compressed between the foot pedal and the pump body via 2 bolts, and the
    > intake hole lines up with a hole at the bottom center of the pump body.
    >
    > Any ideas?

    Since your gauge reads, albeit briefly, we'll assume you haven't broken the gauge itself.

    Silca's gauge reads the pressurized area between the check valve of your pump and the bicycle's
    valve. Air is escaping that area, most likely at the check valve but possibly at any one of the
    threads - check valve cover, gauge to body, etc. Ensure the check valve's rubber seal is smooth and
    doesn't have a bit of swarf stuck in it. Assembling with a drop of paint, pipe joint compound or
    teflon tape would seal the threads. (Since the threaded bits are bronze, you needn't lean on the
    wrench). It could also be something so simple as a worn washer at your tube's valve.

    If you cannot spot the leak right away, a bit of soapy water can be brushed over the joints looking
    for bubbles.

    --
    Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
     
  6. Michael

    Michael Guest

    Update: the problem turned out to be excess grease (from re-greasing the main pump tube) that had
    gotten squished down into the brass cylinder around the check valve. That gunk caused the check
    valve to get stuck in the open position. I just cleaned the whole check valve assembly and it's back
    to normal.

    "A Muzi" <[email protected]> wrote in message news:<[email protected]>...
    > "Michael" <[email protected]> wrote in message
    > news:[email protected]...
    > > When I needed to replace the rubber gasket in the pump head of my Silca Super Pista, I took the
    > > opportunity to take the pump completely apart and re-lube everything. But after I put it all
    > > back together, the gauge stopped working.
    > >
    > > On the push stroke the needle goes to approximately the right pressure reading, but immediately
    > > falls back to 0. The pump works fine - I can verify the pressure with a separate guauge I've got
    > > - but previously the needle would hold at the current pressure as I pumped. It's pretty hard to
    > > read the value now in the split second the needle peaks at a number, especially considering how
    > > close together the gauge ticks are.
    > >
    > > I can't believe I broke the gauge just by taking it off and putting it back on. There's no magic
    > > to how it attaches - it's compressed between the foot pedal and the pump body via 2 bolts, and
    > > the intake hole lines up with a hole at the bottom center of the pump body.
    > >
    > > Any ideas?
    >
    > Since your gauge reads, albeit briefly, we'll assume you haven't broken the gauge itself.
    >
    > Silca's gauge reads the pressurized area between the check valve of your pump and the bicycle's
    > valve. Air is escaping that area, most likely at the check valve but possibly at any one of the
    > threads - check valve cover, gauge to body, etc. Ensure the check valve's rubber seal is smooth
    > and doesn't have a bit of swarf stuck in it. Assembling with a drop of paint, pipe joint compound
    > or teflon tape would seal the threads. (Since the threaded bits are bronze, you needn't lean on
    > the wrench). It could also be something so simple as a worn washer at your tube's valve.
    >
    > If you cannot spot the leak right away, a bit of soapy water can be brushed over the joints
    > looking for bubbles.
     
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