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Old 01-25-09, 06:51 AM   #1
McQz
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Trouble with Presta Adapter

I have read all of the threads I could find re: using Presta valves and haven't found this problem or a solution so far.

We have our first bike with Presta Valves in 30 years. Back in the 70's we had bikes with Presta valves, but not since. We always used a floor or hand pump with a Presta head back then (we were much too poor to own a compressor. Our only power tool was an electic drill.) In celebration of my 60th birthday we bought a Giant FCR2W for my wife and she couldn't be more delighted! I bought a couple Schrader adapters expecting that would stand us in good stead when we had access to a compressor (mine, gas stations,etc.), rather than using the hand pumps.

After a GREAT 10 mile ride earlier in the day, we decided to give the adapters a try last night and had decidedly bad results. We began, innocently enough, by trying to check the air pressure. We were finally able to get a pressure reading using a hand gauge, but it was extremely difficult and the adapter had to be screwed very tightly. We were never able to get air to transfer from my compressor to the tire, but we did mostly deflate the tire trying.

I tried 2 different chucks, one that Ihas a gauge, quick release, and trigger system. I use it all the time to air up our tires and those of every kid in the neighborhood. One time we got a very brief indication of air going in and then we just filled up the short hose between the trigger and chuck. We were shooting for 80# and had the delivery set at 100#. I also tried a typical press on and hold garage type chuck that came with the compressor. It never worked.

We (I) finally used the Presta hand pump to get the pressure back up to 80#, but it probably took 100 strokes, which is why I wanted to use the compressor and adapter in the first place! It seems to me that the problem is that the Presta "stem" is not depressing the spring-loaded pin in the center of the chucks.

Has anybody else encountered problems of this nature? Any ideas about how to get around this? Is there a diffferent kind of chuck that might work? Am I going to have to buy a floor pump with a Presta head and forego the joys our current level of affluence has afforded?

Thanks,
McQ

Last edited by McQz; 01-25-09 at 06:58 AM.
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Old 01-25-09, 07:46 AM   #2
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No problems with adapters. They do have to be seated fully.

Get a floor pump. Even with an air compressor, I cannot get high enough pressure out of it for my road tires (120psi). A decent floor pump is the answer. I buy the tripod style floor pump from Pricepoint. It costs about $15.
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Old 01-25-09, 07:50 AM   #3
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My compressor has no problem getting up over 100 psi. I use it for painting, impact tools, etc. and I keep the tires on my bike at 85# with no hitch. I'd really like to use it and my bride has used it to maintain her own tires in the past. If we switch to a floor pump, I'll be the compressor...
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Old 01-25-09, 08:01 AM   #4
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Before you thread on the adapter, open the presta stem nut and "burp" the tube by briefly depressing the stem to be sure it's free to move. When the stem nut is opened, it will sometimes take 150 psi or more to break the seal at its base if you haven't done it manually.

Good presta adapters have an O-ring in their base to make a good seal against the threaded stem so be sure yours has one.

Most pressure gauges are very difficult to use on bike tires. They require so much air volume to operate that the very act of measuring the pressure changes it. Schrader gauges may not even work on presta tubes with an adapter as the stem depression pin may not reach. There are presta pressure gauges specifically made for bike use and they aren't very expensive.
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Old 01-25-09, 09:26 AM   #5
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Considering that we got air into it last night, I went out and burped the valve and then tried again with the compressor. The "good" fitting with the gauge and quick release head still didn't work. The generic push and hold did. On closer inspection, the cheapie has a MUCH longer stem and the good one's stem is so recessed that it doesn't seem likely that it is even making contact with the presta post before it bottoms out on the adapter.

At least I have a way to do it. Setting the compressor at 85# it measured 82.5# after taking it down to about 60#.

I've ordered the Prestalator so that I won't have to mess with the adapter at home. We've also ordered a couple of Presta pressure gauges.

Thanks,
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Old 01-25-09, 09:48 AM   #6
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If the presta valve stem sticks out a longer amount it may not be fully seated in teh valve body. There is a conical shaped gasket that can still hold pressure. If it sticks out too far it can let go suddenly (like a blow out), leak slowly or work fine until you put on a valve cap or pump head.
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Old 01-25-09, 10:11 AM   #7
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I don't own a presta tire guage. My tires need air every day or 2 and my 12V pumps have built-in guages so I just screw on the adapter, clip on the pump and turn it on. When the guage reads 120, I pop it off the valve and turn off the pump.
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Old 01-25-09, 11:21 AM   #8
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Quote:
Originally Posted by McQz View Post
Considering that we got air into it last night, I went out and burped the valve and then tried again with the compressor. The "good" fitting with the gauge and quick release head still didn't work. The generic push and hold did. On closer inspection, the cheapie has a MUCH longer stem and the good one's stem is so recessed that it doesn't seem likely that it is even making contact with the presta post before it bottoms out on the adapter.

At least I have a way to do it. Setting the compressor at 85# it measured 82.5# after taking it down to about 60#.

I've ordered the Prestalator so that I won't have to mess with the adapter at home. We've also ordered a couple of Presta pressure gauges.

Thanks,
Presta valves don't need to have the stem depressed to add air like schrader valves do. The schrader valve has a spring that keeps it closed while the presta uses the air pressure in the tire to close the valve. Presta valve do, however, stick closed and need a little burp to open them prior to adding air. This is usually accomplished by tapping the valve prior to attaching the chuck. The thread on adaptors usually keep you from tapping the valve and make filling them much more difficult. You need enough air pressure in the line to overwhelm the internal pressure and the seal that forms between the stem and the valve. This can be result in needing pressures way over what you plan on putting into the tire. Typically, I can see line pressure of 90 to 100 psi on a mountain bike tire before the valve will open (45 psi tire pressure) if I biff the burp

Your best bet would be to ditch the thread on adaptors (I've always found them to be pretty useless) and go for one of
these these
for shop/compressor use.
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