theden

Hey guys.

Is there anyway to keep are from shooting out temporarily when disconnected the pump from the valve? I have a pressure guage on the pump, and generally give it a few extra psi knowing that some amount of air will come out from the tire when I disconnect the pump. Anyway to avoid this?

CommuterRun

Get a stand alone pressure gauge and check the tires after you've finished airing them up. I think you'll find you're not loosing enough to make any difference. I found that all the rushing air I was hearing when disengaging the pump from the tire stem was coming out of the pump and hose.

Patriot

Understanding how the presta valve works to begin with, kind of answers your question. I always wondered if the same was happening as well, until I really looked at how it works.

When you clamp the nozzle over the presta valve, you aren't depressing the stem at all in order to get air into the tire. The stem stays seated, and the clamp just seals itself around the valve. When you pump air into it, the higher air pressure from the hose pushes the presta vlave down to let some of the air in. That's why, when the vlave opens, you will see a slight drop in pressure on the pump gauge, because the air pressure in the pump builds up higher than what's in the tube in order to push the stem in.

Once you complete the downstroke on the pump, the pressure in the pump hose drops just a little, and the presta stem automatically closes without losing any air. So, when you unclamp the nozzle from the stem, the only air you hear coming out is what's leftover in the pump hose, because the presta stem is already seated.

Hope this explanation helps.

Happy riding

Sasquatchula

Slightly OT, but I have a recurring problem in that when I air up and remove the pump nozzle I've on occasion ripped the valve stem from the tube Not totally, just enough to cause a leak. Just me?Thag to strong? Or this happen to others?

Moistfly

It happens to me too ... but in my case it's the fault of the pump itself being poorly desgined and holding onto the stem threads even when unclamped. To prevent this I simply buy tubes with unthreaded valve stems ... haven't had that problem since

Patriot

Well, when you remove the nozzle from the stem you don't physically rip it off. You need to hold the nozzle and gently release the clamp before you remove it from the valve. And always pull it straight off, never try bending or wiggling it back and forth to get it off the vlave stem.

Ohio Trekker

YEP one time, the valve came right out of the rim. Boy was I shocked.Just glad it happened at home and not out on the road. Although I always carry a spare, it's still a hassle on the road as compared at home in the garage.

Trekke

every time I have had that happen I find that the tube is dry rotted. Usually happens if bike has been up all winter and tube just about falls apart in your hand.

Sasquatchula

Yeah, I'd agree it's the nozzle. I've tried to be as carefull as possiible, but you get that creeping sensation when it's gonna happen. It's super frustrating. I have been guilty of wiggling. Great that tubes are cheap. I'd learn supa-fast if a tube was 50 bucks a pop, I bet

Now unthreded stems is something I'd never thought of. Nor seen, to my recollection. Thanks for the tip, I'll have to keep my eyes open for them.

Cheers!

Hemlock

"Thag too strong?"

Sasquatchula, that made my day! Me love talk caveman! Caveman 3rd person best ever!

Sasquatchula

hemlock

What mean caveman?



/Me like talk much, too!

Hemlock

Some friends and I got WAY carried away with speaking in broken 3rd person (which we referred to as "caveman") to the point that it became subconscious. That made for some pretty funny moments.

Me have to explain before, not know who know or who think me idiot.

Jakey

Unthreaded valves rule.