>I've never had any luck with inflating Prestas -- must have something to do with the little cap you
>have to unscrew. Anyone have the secret of Prestas for a mechanically challenged klutz like myself?
I'll try. First, the parts of the valve. There's a plastic cap on the end of the valve stem.
According to Sheldon this isn't necessary other than to protect a folded tubular (or tube, I guess)
from being punctured by the end of the valve core shaft. It also keeps dirt off the actual valve
cap, which is the little knurled nut that screws in to hold the valve closed or out to allow the
valve to open under pressure.
(I've seen and used Continental tubes where the fit of the plastic cap was tight enough to unscrew
the valve core, which is a separate part on these tubes. I have yet to figure out why, it's the only
brand of Presta valve I've ever seen with this "feature".)
If you're using clincher tires, the valve stem is usually threaded to accept a locknut. The locknut
is there to keep the stem from disappearing into the rim so you can get a pump on it. Tubular tires
usually have smooth stems without lockrings, you don't want a tubular locked to the rim if you roll
the tire off, and besides the valve can't drop down as it's supported by the casing.
So you have clincher tires and you're ready to pump. Take off the plastic cap and set it aside, even
if you can't find it later it isn't a critical part. The yellow ones are easier to spot later. If
its dark and raining, which it usually is, you can stick it in a pocket or something.
Unscrew the real valve cap (the knurled nut on the valve core shaft). It can't come off, but you
don't need to screw it all the way to the end of the shaft, close, though. If there's any pressure
in the tube push the valve stem in to break the seal, you should feel a slight resistance until the
valve breaks free of its seat. Air will escape, let it pop back. The more air you let out here the
more pumping is required later.
Now prepare to apply the pump. If a floor pump, I like the valve at the bottom of the wheel,
pointing up. If a frame pump, I like it at the top pointing down. This is so you can remain
standing, in this hypothetical rain storm.
Be sure the valve stem is perpendicular to the rim.
Practice at home with the pump you actually intend to use. This is because the pump chuck (the part
that fits on the valve shaft) usually has a locking lever that engages the collet (the part of the
chuck that grabs the valve stem). Most of these are locked when the lever is up, but some are locked
when the lever is down, know beforehand which kind you have.
With the lever in the unlocked position slide the chuck on to the valve stem until it bottoms out.
If it doesn't slide on easily it's very likely in the locked position. Do this carefully, because
it's possible to bend the valve core shaft. Now engage the locking lever.
You are ready to pump. In the case of the floor pump, pump away until the handy gauge (whose
calibration error is known to you) registers the appropriate pressure. Unlock the pump chuck and
pull straight off the valve, don't wiggle it. Clost the valve cap (the knurled nut on the valve core
shaft) until it is finger tight. Replace the plastic cap, or not, as it strikes your fancy.
With a frame pump, the steps are almost the same except in this case you are the pump support. The
idea is not to allow any forces that move the valve stem around. You do this by holding the air end
of the pump in a fixed position with one hand and moving only the piston, not the pump body, with
the other hand. This is much easier to accomplish in fewer strokes with a full sized frame pump than
with a minipump. You won't usually have a gauge here, or if you do you won't be able to read it in
the dark and the rain, so get useed to what a properly inflated tire feels like ahead of time.
Alternatively, stop pumping when you get tired, so to speak.
To remove the frame pump, unlock the lever and give the business end a bang with your fist such that
the chuck pops off along the axis of the valve stem. Close the valve cap and try to rember where you
put the plastic thingy.
A note on gas station air pumps: Their pressure gauges are notoriously slow to react and frequently
unreliable. It is easily possible to blow a tube out with them, so don't use them unless you have
your own pressure gauge on hand, and then use them in short shots only. If you have your own pump
stay away from them, they are only for emergencies and not for regular use.
A note on Presta to Schrader adaptors: No reason not to carry one, you may need it if your own
pump dies.
--
_______________________ALL AMIGA IN MY MIND_______________________ ------------------"Buddy Holly,
the Texas Elvis"------------------
__________306.350.357.38>>
[email protected]__________
