Presta Valves

oliverevilo

I know I know, this is stupid, but I just got a new bike with presta valves which are foreign to me. After unscrewing the little thing on the end and trying to attach the pump all the air just comes out. The pump i'm using isn't good, it's a Topeak Pocket Rocket which claims to be presta compatible too...so i changed round the little rubber insert thing inside it but when i push it over the valve stem it doesn't go far enough to stop air just spilling out...what am i doing wrong here? Does this pump not work with presta really? do i need some kind of additional adapter?

thank you!

nicklouse

most pumps need locking on to the valve to work.

steelo

The idea with a presta valve is that the pressure of the air in the pump forces the needle down and the air is pushed into the tube. Make sure the brass 'lock-nut' thing is unscrewed from the valve, but still attached. Carefully place the pump over the valve, should cover about 5-8mm of the valve, lock the pump in place using the lever. Inflate the tyre.

When the pump is placed over the valve air should not be rushing out. Air only escapes from a presta valve when you press the lock-nut down after unscrewing it. Pressure within the tube keeps the valve sealed.

oliverevilo

hmmm. the tire is completely flat at the moment... what is the significance of unscrewing the nut at the top (rim end) of the valve? I have tried locking it but the pump doesn't seem to go far enough over the valve stem to lock on when i flip the lever up!

Lesser Spotted Lurker

Shamelessly paoched from Sheldon Brown

Presta valves don't use a spring, but they have a captive knurled nut to hold the core tight. Before you can pump up a Presta tube, you must loosen this knurled nut. It is also a good idea to tap the end of the pin, to break the seal loose, because they are sometimes sticky. After inflating the tube, you should re-tighten the valve nut to keep air from escaping.

dennisn

Best bet is to find someone to show you. It can be tricky at first.

Dennis Noward

Jimbob_no5

i hate presta valves, has anyone else had the problems of pinch punctures?? i had 4 in a maxxis downhill tube, the rim and tyre were clean and the pressure was at around 50psi, anyway ive moved to the panaracer super downhill tubes

paddy mtb

i got prestas on my chucker (got the maxxis freeride ones) and there gr8 i rode my frends bmx and managed 2 force the air out of his crapy schraeders bt i s'pose its down 2 personal taste

dennisn

kona_cowan_rider wrote:

i hate presta valves, has anyone else had the problems of pinch punctures?? i had 4 in a maxxis downhill tube, the rim and tyre were clean and the pressure was at around 50psi, anyway ive moved to the panaracer super downhill tubes

Why would a presta valve tube be any more prone to have a pinch flat than a schrader??
Is that what you're saying???
I'm not a mountain biker, so fill me in.

Dennis noward

cunning-stunt

Basically,it wouldn't.
I ran Presta on my Trek for 7 years with about 4 punctures