Presta
Valves
(a
beginners guide)
from Dr. Schraedor
Shraeder and presta are the types of valve stems used on innertubes.In
the U.S., shraeder valves are used on everything from cars to bicycles,
so it's a common style. However, presta valves are common in Europe,
and found on sew-up tires and ultra-lightweight clincher
tubes that need an aerodynamic, lightweight valve-stem, such as
higher end bikes. This is probably why more expensive bikes are sold
with presta and lower end bikes are sold with schraeder.
Presta Valve Basics
Before you can put air in a presta valve, you must unscrew its
tip. Look closely and you'll see that the valve's tip is knurled
to make
it easy to turn it by hand. Unscrew it all the way (counter-
clockwise) and then press the tip down until some air escapes. This
is important because it frees the valve, which usually sticks after
being sealed for a while. Until you free it, it can be difficult to
impossible to put air into the valve.
Here are six other valuable valve facts:
- Replaceable Presta Cores
Some presta valves have replaceable cores. You can tell if yours
is by looking for wrench flats on the sides of the valve just below
the
tip. A replaceable core is a nice thing if yours gets damaged
somehow. However, it's also something to check regularly because
if it loosens, you'll develop a slow leak and get flats all the
time. The solution is simple, just snug the valve by tightening it
with
an
adjustable wrench (turn clockwise).
- CO2 Cautions
Take extra precautions using CO2 inflators on valves with replaceable
cores. The drastic pressure drop as the CO2 leaves the cartridge
super-cools the cartridge and adapter. In damp weather, this
can freeze the cartridge to the valve. And when you unscrew the
adapter, you extract the valve core with it, deflating the tube.
To prevent
this, after inflation, squirt the valve with some water from
your
water bottle to de-ice things and then carefully remove the
adapter from the core.
- Converting Schraeder
Holes For Presta Valves
If you use a presta valve tube in a rim drilled
for schraeder
valves, you'll notice that the hole is too big. This isn't a
problem unless
you ride with low air pressures as some off-ride cyclists
like to. In that case, the presta valve may creep as the tube shifts
inside the
tire. This can lead to a bent or broken valve over time.
To
prevent this miscue, install rim grommets, O-ring-like rubber washers
that
fit in the valve hole reducing its diameter to match the
Presta's.
- Protect
The Valve When Pumping
An important tip about valves is that they're
not indestructible
and they're at the most risk when you're pumping up the tire
using
your
frame-mounted pump. To protect the valve, always support
it by holding the end of the pump that's on the valve in such a
way
that you can hook a thumb or finger over the tire. That way,
as
you push
to inflate the tire, you're pushing against your hand and
not the valve, which will bend or break if you push against it
alone.
- Valve Nuts
A common question with presta valves is whether or
not it's important to install the valve nuts (knurled metal rings
that
are
used
with
threaded valves). Not all presta valves are threaded
from top
to bottom. But, if yours are threaded, there's a good chance
that there
are valve nuts on them. These can make it easier to
inflate the tire because they hold the valve proud of the rim making
it easier to
get the pump head on them. Be sure not to tighten them
too
much, however, or they'll be difficult to remove by hand when
you have
to fix a
flat
on the road or trail. Over tightening the nut can also
put pressure on the valve/tube junction where it passes through the
rim and cause a flat.
- Dealing With Slow Leaks
One final tip: when you're
searching for a slow leak, don't
ignore the valve. Sometimes valves fail and
air seeps out. To check,
put a little spit on the end of the valve and
stare at it for a few
seconds. If the valve is leaking, a bubble will
form. Often you can tighten the valve and the leaking will cease.
If this
doesn't do the
trick on a schraeder valve, try removing the valve
core, putting a drop of oil on the spring and reinstalling the
core.
This will
usually stop the leak.
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Most
quality bicycle pumps sold today are convertible and will inflate both
schraeder and presta valves once the pump head is unscrewed and the
parts are
reinstalled
per the manufacturer's instructions.
 If
your schraeder pump is not convertible, a schrader pump to presta valve
adapter like
the one pictured can be bought for around $1
 Many
racers use CO2 or canned air cartridges to inflate their tires quickly
in a race.
Dr. Schraedor demonstrating
the proper way to check the tightness of your valve nuts.
"Turn your head and..."
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