Presta-Valve Basics
Before you can put air in a Presta valve, you must unscrew its tip. Look closely and
you will 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:
1. 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).
2. 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 waterbottle to de-ice things and then carefully remove the
adapter from the core.
3. Converting Schrader Holes For Presta Valves
If you use a Presta valve tube in a rim drilled for Schrader 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.
4. 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.
5. 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. Overtightening the nut can also put pressure on the valve/tube
junction where it passes through the rim and cause a flat.
6. 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 does not do the trick on a Schrader
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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