John Forrest Tomlinson said:Quoted message said:John Forrest Tomlinson said:On 23 Aug 2006 07:54:33 -0700, [email hidden] wrote:
>> http://www.nashbar.com/profile.cfm?category=106&subcategory=1075&brand=&s
>> ku=17232&storetype=&estoreid=&pagename=
>
>Problem with the Nashbar pump is the pump head. I bought a couple of
>the Nashbar spare pump heads and tried them on some of my Silca pumps.
>The automatic valve inside the pump head that switches between the
>schrader or presta hole does not work all the time.That pump does not use an automatic valve -- it has separate holes for
the different valve types.What do you think keeps the air from coming out both the schrader and
presta holes at the same time on the Nashbar pump head? Magic? There
is an automatic valve inside the pump head that senses the amount of
pressure in each hole and directs the air to the hole with the most
back pressure. The hole with the inner tube valvve in it. The
automatic valve closes the other hole so no air comes out it while
pumping.What toggle switch? Is that the same lever that tightens the pump
head around a presta valve?Quoted message said:
As stated, the problem with the cheap Nashbar pump head is that
automatic valve does not sense which hole to direct the air into. So
you put the inner tube valve into the appropriate hole, flip the toggle
switch, start pumping, and the air keeps coming out the other hole.Quoted message said:For internet bicyclists this is of no concern since they don't actually
ride bikes. But for people who ride bikes, spend some more money and
get a pump head that works.I ride a bit. We'll see if mine fails. It's working now and seems
good.JT
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Dear John,
I think that there's some confusion about the varieties of dual pump
heads.
Here's an older model:
http://www.performancebike.com/product_images/400/40_1452B.jpg
It's a side view, but there are two holes on the same side of this
pump head, separate outlets for Presta and for Schrader. Sometimes the
valve inside the head sticks and air goes whooshing out the open,
unused hole. Pushing the tire against the base of the valve stem as
Ryan suggests will wake the valve up. So will an irritable rap against
the floor.
The lever doesn't control the valve. It just tightens the seal around
a Presta valve stem. You don't unscrew and reassemble anything to
switch between Presta and Schrader.
I think that this is the same 2-hole design, two holes on the same
side of the pump head:
http://www.performancebike.com/product_images/400/40_1604B.jpg
The curves indicate the two holes that you can't see.
This is the kind of pump that you're using:
http://www.performancebike.com/product_images/400/40_1872C.jpg
I'm not familiar with it. If it has only one outlet, then there's no
need for a valve. A single outlet must either work on both Presta and
Schrader without any fuss, or else you have to unscrew the nozzle,
flip an interior piece, and reassemble things.
If it's a two-hole design, then the holes are opposed, not on the same
face, and either an automatic valve works so well that you've never
noticed it, or else the valve is controlled by the yellow lever that
also tightens the seal around the Presta.
This kind is clearly a one-hole:
http://www.performancebike.com/product_images/400/40_2176B.jpg
Either it has a very clever one-hole design that fits both kinds of
valve stems without any fuss, or else you have to unscrew it, flip the
interior piece, and reassemble it to suit your tire. But it won't need
any interior valve.
Cheers,
Carl Fogel