Presta valves
 

Anyone have issues with presta valves? This is my first experience with them and I have a slow leak somewhere, either in my tube, or the valve. I have notice that when I have lost air and go to refill the valve screw is a little loose when I go to unscrew to fill.
What do you think? Is it the valve or do I have a hole in my tube. Hate to take everything apart and look for hole if its the valve.
Thanks Beth

Best way to find out is put the tube under water, but you'll want to take the tube out for that. It might work putting some dishsoap on the valve to see if it creates a bubble from leaking. I doubt it is the valve though -- I've used them for years without issue. More likely a small hole in the tube.

I have Presta valves on a couple of my bikes and have no issues. Recently due to a trip out of town I left my bike untouched for over a week, and when next I rode it I only had to pump in less than 5 pounds in the front tire and less than 10 in the rear.

Not sure what you mean by the little screw, but I presume you are talking about the valve. This valve must be loosened to pump in the air, then it should be screwed down tight again when you are done, which firmly seats the valve. When you press your pump on to the valve to fill it, you do not need to push it on so far that the valve opens. Doing so can bend the stem, which may prevent it from seating. As long as you get the pump on the stem and the lever locked, when you pump the pressure differential will override the stem and allow the air into the tube.

The nut on the outside of the Presta valve should normally be loosened, but should be snugged down against the wheel when inflating the tube. When finished, loosen the nut a little. This nut, when loose, allows the stem to "float" a little in the hole in the rim, but when tightened prevents you from damaging the valve/tube joint by pulling it with your pump.

Presta valves are superior to Schraeders in that the seating of the valve in the stem is not just done by a spring, as on the Schraeders, but is both spring seated and mechanically seated by the screw. Also, because the Presta is smaller in diameter, it requires a smaller hole in the rim so rims are stronger.

Some presta valves have cores that can be removed; you might have a loose valve core. I've had headaches with them before, wasting a few CO2 cartridges for no good reason while out on a ride without better tools. If that's the case and you can't get it tight, replace the tube. Presta tubes are generally easy to use and I prefer them over Schraeders.

I'd suspect a small leak in the tube itself.
While I am sure it is possible for the valve to leak, I haven't personally seen an undamaged* presta valve leak in more than 30 years.

* I have experienced leaky valves if the stem (the little shaft that comes out, with the knurled nut that you tighten down) gets bent.

Here how I check my presta for leak at the valve stem. I would screw the valve close after filling my tire. Then I would screw a Presta to Schrader valve adapter to the stem. Fill the opening with some soapy water and watch for bubbles. Reason for closing the valve is to give some room inside the adapter for the soapy water. If you don't have an adapter, you should buy one anyway as part of your flat tool kit.

A pinch flat between on the tube between the tire and rim may result in a slow leak. That's what happen to me as I was leaking 30 psi in 5 days when normally I lost only about 5 to 10 psi a week. Somehow the same pinch that created the hole also was sealing it until the rip of the hole got passed the area that was pinch.

There's no spring in a presta valve.

OP, unlikely it's the valve, but you can check by submerging a portion of the wheel in a tub and checking for bubbles at the valve. Probably easier to just take the tube out and check the whole thing, though.

Some presta valves have removable cores -- I've had them work a little loose before.

why do they even bother to make those removable core presta valves? what's the advantage? it seems to me that all they accomplish is having another potential point of failure in the valve stem. i have bought some tubes with removable core valves by accident, but I now make sure to only buy the good old fashioned tried-and-true prestas with the non-removable valve cores.

I always thought the ones with the removable cores were the old fashioned ones. ;)

I've bent the threaded part of the valve plunger above the tiny nut before. I was able to straighten it out enough so that it would still open, but just barely. There's always a chance that one could get gummed up and not seal correctly. Maybe this was a bigger problem a few decades ago. My older brother rode everywhere back in the 70's. His old Peugeot sported "sew-ups" or tubulars which are kind of pain to put on your bike. He used to keep extra valve cores around because the last thing he wanted to do was replace a tube if he didn't need to.

My favorite presta-valve core story was from a couple of winters ago during a snow storm. I was at an intersection waiting for a light that typically takes forever. I thought I'd get better handling in the snow by dumping a few PSI from my front tire. I had to remove the valve cap first and I was surprised at how hard it was to turn. Figuring it was frozen I kept at it. Finally it came off, and along with it was a big whooshing sound. The valve cap had froze on and I had unscrewed the whole core.

Doh !

perhaps, i don't know the history of presta valve development. i only know that i won't ever make the mistake of buying removable valve cores tubes again.

I've always been curious why both Presta and Schrader exist-
Why didn't one win out over the other? (Like VHS over Beta, or Blu-Ray over HD)- It just seems it should be standardized-
I say make a Schrader in the same slim profile as a Presta!
i've never had to change a tube for a flat in the last ten years,
Just from snapping or bending the stem of a Presta!

God lord, don't do that. The last thing we need is a third (or fourth if you count that crazy European one) standard.

As for the removable valve core, is does have some advantages. If you do happen to bent the captive nut, you can replace it, if you want to run sealant, you can just put it in without having to cut open your inner tube, and if you happen to run deep profile rims, you can just use an extender, you don't have to use a special inner tube.

Dunlop for the win!


http://upload.wikimedia.org/wikipedi...nlop_valve.jpg

Of course they are. It always takes a while for a product to devolve into non-serviceable garbage.