Top Dog track pump

On 2006-04-02, Brendo (aka Bruce)
was almost, but not quite, entirely unlike tea:

Quoted message said:

I'm assuming htese type of things are standard, but basically you slip
the nozzle over the valve, lock it on, and pump. My query is that when
you lock it on, the pressure guage reads zero. After pumping it goes up
to 110-120psi, then I release the nozzle. I would have thought that when
you locked the nozzle on the guage would read what the current pressure
is in the tyre. Is the zero reading normal, and is that just the way the
skinny Presta valves work? Or am I doing something wrong (which is not
unheard of)

First time I tried my pump, it would read zero straight off -- I
occasionally got it to read the proper amount. I thought something
was broken. Then someone pumped up my tire for me, and I saw that it
read zero straight off. Then he started pumping anyway, it "popped",
and started reading properly.

Damn, that wasn't in the instruction book.

Dunno the physics behind it, but it seems normal.

--
TimC
"The Internet is the most powerful stupidity amplifier ever invented.
It's like television without the television part." -- James "Kibo" Parry

TimC said:

First time I tried my pump, it would read zero straight off -- I
occasionally got it to read the proper amount. I thought something
was broken. Then someone pumped up my tire for me, and I saw that it
read zero straight off. Then he started pumping anyway, it "popped",
and started reading properly.

Damn, that wasn't in the instruction book.

Dunno the physics behind it, but it seems normal.

When you first hook the pump over a Presta valve, the pressure read by
the pump is just standard atmospheric pressure -- there's no escape of
air from the main tube that would cause it to be able to "see" the
pressure of the tyre. Start pumping, and eventually, the pressure in the
pump will be sufficiently higher than the pressure in the tyre for the
valve to open and let the pump's air in. At that point, the pressure
gauge will be accurate (or as accurate as those things can be, anyway.)

You don't get that on Schrader (aka "car tyre"😉 valves because the
process of putting the pump on the valve opens the valve, meaning that
you automatically get equalisation between the pump and the tyre.

--
My Usenet From: address now expires after two weeks. If you email me, and
the mail bounces, try changing the bit before the "@ to usenet".

Stuart Lamble said:

When you first hook the pump over a Presta valve, the pressure read by
the pump is just standard atmospheric pressure -- there's no escape of
air from the main tube that would cause it to be able to "see" the
pressure of the tyre. Start pumping, and eventually, the pressure in the
pump will be sufficiently higher than the pressure in the tyre for the
valve to open and let the pump's air in. At that point, the pressure
gauge will be accurate (or as accurate as those things can be, anyway.)

You don't get that on Schrader (aka "car tyre"😉 valves because the
process of putting the pump on the valve opens the valve, meaning that
you automatically get equalisation between the pump and the tyre.

That's not what I get. My track pump (dunno brand) shows the pressure in
the tyre as soon as it connects, regardless of valve type. If it shows
zero it means I have a bad connection (hate those tubes with the little
valves).

DaveB "looking for excuses to stop studying"

DaveB said:

Stuart Lamble wrote:
That's not what I get. My track pump (dunno brand) shows the pressure in
the tyre as soon as it connects, regardless of valve type. If it shows
zero it means I have a bad connection (hate those tubes with the little
valves).

*shrugs* different brands, different designs, etc?

--
My Usenet From: address now expires after two weeks. If you email me, and
the mail bounces, try changing the bit before the "@ to usenet".

DaveB said:

Stuart Lamble said:

When you first hook the pump over a Presta valve, the pressure read by
the pump is just standard atmospheric pressure -- there's no escape of
air from the main tube that would cause it to be able to "see" the
pressure of the tyre. Start pumping, and eventually, the pressure in the
pump will be sufficiently higher than the pressure in the tyre for the
valve to open and let the pump's air in. At that point, the pressure
gauge will be accurate (or as accurate as those things can be, anyway.)

You don't get that on Schrader (aka "car tyre"😉 valves because the
process of putting the pump on the valve opens the valve, meaning that
you automatically get equalisation between the pump and the tyre.

That's not what I get. My track pump (dunno brand) shows the pressure in
the tyre as soon as it connects, regardless of valve type. If it shows
zero it means I have a bad connection (hate those tubes with the little
valves).

Your pump must have some "feature" that pushes in the presta valve end.
Tim's "pop" is probably caused by a sticky presta valve. the easiest
way to aleviate this is to push the valve in by hand a little until it
lets some air out. Then you're good to pop the pump on and away you
go.

Quoted message said:

DaveB "looking for excuses to stop studying"

Worked it out!! You have to unscrew the bit at the top of the valve
before it inflates or deflates!! Spot the new rider!! Thanks for all the
help though!