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schrader vs. presta

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schrader vs. presta

Unread postAuthor: chartreusesnot » Sun Apr 12, 2009 2:09 am

Im thinking of using either a schrader or a presta valve as a very compact check valve in a mini pneumatic. I am fairly certain this would work. My question is what do you guys think is the cracking pressure of schrader valve? The difference between schrader and presta is that schrader has a spring holding it closed, presta doesnt. So cracking pressure for presta is 0, but what is it for schrader?
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Unread postAuthor: qwerty » Sun Apr 12, 2009 2:22 am

I think you should use a schrader valve because i know someone who had used them up to 700psi
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Unread postAuthor: john bunsenburner » Sun Apr 12, 2009 3:28 am

Well the crackign pressure can't be too high, i would guess around 30psi or so. It wouldn't really matter in a mini as I persume you will use a shock pump and get this baby to about 400psi, which a shrader can hold without a problem.
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Unread postAuthor: Biopyro » Sun Apr 12, 2009 5:17 am

I remember hearing 70psi before, but I'm not 100% sure if I'm thinking about the same thing as you. By cracking pressure do you mean the pressure the air before the schrader must be before it opens?
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 12, 2009 8:29 am

Biopyro wrote:I remember hearing 70psi before, but I'm not 100% sure if I'm thinking about the same thing as you. By cracking pressure do you mean the pressure the air before the schrader must be before it opens?


That would be the pressure difference before the spring is overcome, Gipetto had tested it and found it to crack at 70 psi, I did some tests with mine and it came to approxumately the same.
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Unread postAuthor: frankrede » Sun Apr 12, 2009 9:43 am

A presta makes a great pilot valve, seeing as the core is exposed but it is only convenient if you have a air chuck made just for presta valves. Using a schrader adapter for a presta is a pain
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Unread postAuthor: chartreusesnot » Sun Apr 12, 2009 12:52 pm

I think 70 psi is a little high... so I'll go with presta. Frank, the chuck doesn't matter because im just going to be surrounding the pump side of the presta valve with high pressure, so it will automatically open an fill the other side, like a check valve, just really small.
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Unread postAuthor: Daltonultra » Sun Apr 12, 2009 2:06 pm

Why not just order an actual small check valve? http://www.mcmaster.com has a wide assortment, most of which crack at 1psi differential or less, and run up to 3000psi ratings.

http://www.mcmaster.com/#check-valves/=1ezd8g
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Unread postAuthor: chartreusesnot » Sun Apr 12, 2009 3:27 pm

1. Those are 1/8" which is significantly larger than a presta valve.
2. Those are 10$ + shipping
3. I'm not patient enough to wait for that to ship, and I have a presta valve.
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Unread postAuthor: VH_man » Sun Apr 12, 2009 4:07 pm

Use a Presta for a Check Valve.

they have absolutely NO cracking pressure at all. In fact, You might have to attach your own spring.

Schraders make junk check valves unless the core is modified to have no spring.

my only warning is that Presta's have very thin walls, So take care in taking them over 300 PSI or so.
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Unread postAuthor: maverik94 » Sun Apr 12, 2009 7:42 pm

sorry, but I dont quite understand what you mean by: cracking pressure. Could someone explain that?
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Unread postAuthor: VH_man » Sun Apr 12, 2009 7:53 pm

Cracking pressure is the pressure required to open the valve

to put it simply, until you have a pressure differential of 70 PSI on the flow side, you wont get air through the other side of the schrader.

In case you didnt understand that (im not insulting you in ANY MEANS i just explain things poorly sometimes, so im trying a new tactic) there must be 70 PSI present on the "in" side for it to begin flowing to the other side.
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Unread postAuthor: Hotwired » Sun Apr 12, 2009 11:27 pm

Presta valves have thin walls?

I'm looking at one of each I use myself and they have pretty much the same wall thickness.

Which means the Presta is better in that department because its stem isn't as wide.

Realistically the valve stems are not going to fail. Unless you have them clamped and swing a hammer against them.

I'd not be in favour of having to pump an extra 70 to get the pressure I was after though ^^
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Unread postAuthor: chartreusesnot » Sun Apr 12, 2009 11:58 pm

Anyone have an estimate for the bore on a presta valve? From what I can tell its about 3 millimeters... I trying to figure how much force would be necessary to open it under something like 300 psi.
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Unread postAuthor: VH_man » Mon Apr 13, 2009 6:33 pm

A presta has no spring in it.

dependign on its orientation, we can either assume its constantly open, level, and therefore neutral, or upside-down, and therefore closed with the force weight of the presta core itself.

If i had a spare presta core, Id do the math for ya.
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