Proper Presta Valve length???
11-10-03, 09:56 AM
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Proper Presta Valve length???
I'm only assuming this is my problem yet I could be wrong. I'm having problems inflating my tires with the new Park Home floor pump. I have a set of Mavic CXP21's with standard size Presta valves. I unscrew the valve all the way out until it stops itself. Then I push the pump head all the way down and lock it. This is where the problem starts, the tire pressure is at 0 and as I pump the pressure builds to extreme rates until it forces the valve to push in and receive air as it should. At this time the valve is forced in and the pressure gauge reads the correct tire pressure. This can't be right so I assume my valves are to short. I have a good inch protruding from the rim, I guess it's not enough???
11-10-03, 09:59 AM
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An inch protruding from the rim should be plenty of stem. It sounds more like the valve is sticking. After you unscrew the valve, push it in and pull it out several times by hand before you put the pump head on it. See if that helps.
Another possibility is that you are actually pushing the pump head on too far and closing the valve up.
Another possibility is that you are actually pushing the pump head on too far and closing the valve up.
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11-10-03, 11:38 AM
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Yep, as Mr. RegularGuy sez......sticky valve which happens all the time......nothing wrong. As they say, length doesn't matter.
11-10-03, 12:31 PM
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Yeah, like mentioned before, get into the habit of simply pushing in the valve til you head the air comes out, then put the pump head on and lock it. Sometimes if the pump head is already on the stuck pin, when you release the air in the pump, that will sometimes "unstuck" 
the pin but the safe method is to push it with your finger for a bit...
You can get "long" (36mm) presta valves too but 1" over the rim should be long enough. You can get super long presta valves that are 80mm (Vredestein makes the only ones that I have seen) but those are only for super deep dish rims like the Zipp 404s.
Jay
the pin but the safe method is to push it with your finger for a bit...You can get "long" (36mm) presta valves too but 1" over the rim should be long enough. You can get super long presta valves that are 80mm (Vredestein makes the only ones that I have seen) but those are only for super deep dish rims like the Zipp 404s.
Jay
11-10-03, 12:31 PM
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some REALLY sticky valves won't let you put air in until the tube is well deflated... so you might have to let out alot of air before you can pump.
11-10-03, 12:39 PM
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You only need to rotate the valves a turn or so. If you can press them in, and hear air rushing out, that is good enough. If you unscrew them more, you risk bending the needle as you apply the pump.
A lot of people use valves without the retaining screw at the rim. I like this feature, it helps keep everything in place when you push the pump head on.
Those extra-long valves, and ones with no outer thread or locknut are designed for deep section V rims, not for std box-section rims.
A lot of people use valves without the retaining screw at the rim. I like this feature, it helps keep everything in place when you push the pump head on.
Those extra-long valves, and ones with no outer thread or locknut are designed for deep section V rims, not for std box-section rims.
11-10-03, 12:59 PM
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CXP21s are relatively deep aren't they? you just have to push the thing on from the tyre side as well. try long valves and you'll get better purchase on the valve. pricey though.
11-10-03, 07:07 PM
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Pump should grab the valve with only 0.5-0.6" of
valve protruding beyond rim. If pump is new,problem
is not pump, but valve as others have stated. I have
one such sticky valve on one of my bikes. You can
pop the opened valve with a finger 2-3x, with air
released each time and then put pump on and valve
won't open til pump gets to 175#, then operates
normally thereafter. Holds air ok. One of the vagaries
of presta valves. Steve
valve protruding beyond rim. If pump is new,problem
is not pump, but valve as others have stated. I have
one such sticky valve on one of my bikes. You can
pop the opened valve with a finger 2-3x, with air
released each time and then put pump on and valve
won't open til pump gets to 175#, then operates
normally thereafter. Holds air ok. One of the vagaries
of presta valves. Steve
11-10-03, 08:20 PM
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I've had the same problem with my Mavic's. I unscrew it, push in the stem to make sure the valve is working, then attach the pump head. I find that if I give the pump a series of quick short pumps, the valve unsticks fairly quickly - then the gauge works correctly. I thought it was just the valves on my tubes, but i don't have any trouble with my other bike with Bontrager rims. Glad to see I'm not alone with this problem. Good luck.
