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shrader as check valve?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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shrader as check valve?

Unread postAuthor: mach10 » Tue Apr 07, 2009 4:28 pm

I was wondering if a shrader could be used as a check valve for use in a piston valve or any thing else?
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Unread postAuthor: daniel323 » Tue Apr 07, 2009 4:30 pm

a schrader is a small check valve

.. so yes
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Unread postAuthor: daberno123 » Tue Apr 07, 2009 4:30 pm

Sure it could, although make sure you take the spring out of it first, or you're looking at cracking pressures of ~70 psi IIRC.
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Unread postAuthor: mach10 » Tue Apr 07, 2009 4:35 pm

by cracking pressure do you meen the pressure at witch it fails, and why would taking the spring out help?
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Unread postAuthor: daberno123 » Tue Apr 07, 2009 4:41 pm

By cracking pressure I mean the pressure at which the valve "cracks" open, allowing air through. Up to that pressure the valve is closed.

However, unless you have a piston with a near 100% seal, a check valve is quite pointless, as most of the air will leak around the piston anyway. If you really think your piston deserves one though, a sliding o-ring type check valve around the piston would be easier and have more flow than a shrader.
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Unread postAuthor: mach10 » Tue Apr 07, 2009 4:48 pm

ohh ok sory one more question how do you get the sprinh out I tryed to figer it out but I coulden't so I thout i'd ask rather than brake it
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Unread postAuthor: Hubb » Tue Apr 07, 2009 4:53 pm

You can get a special tool to help with that. It looks like this.
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Unread postAuthor: mach10 » Tue Apr 07, 2009 4:56 pm

any way to do it without a special tool?
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Unread postAuthor: Hubb » Tue Apr 07, 2009 4:59 pm

I've successfully used a small pair of needlenose pliers, but this tool makes it so much easier. They usually cost not more than 5 bucks or so.
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Unread postAuthor: mach10 » Tue Apr 07, 2009 5:14 pm

could you like tell me exactly how cus i have know clue how to
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Unread postAuthor: Hubb » Tue Apr 07, 2009 5:20 pm

mach10 wrote:could you like tell me exactly how cus i have know clue how to


The interior of the valve will screw out.
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Unread postAuthor: mach10 » Tue Apr 07, 2009 5:26 pm

I know I touk out the interior of the valve but I still cant get to the spring
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Unread postAuthor: Hubb » Tue Apr 07, 2009 5:39 pm

You know, I got to thinking about this: If you build an airtight piston and use a schrader valve for a check valve, and the schrader opens at around 70 psi, there would be no doubt that the piston would be seated before the schrader is opened. If you plan on using this setup on something that is going to handle more than the cracking pressure of a scrader, and you are intent on using the schrader as a check valve, then why do you need to remove the spring?

As far as your above statement, I've never removed a spring from a schrader, as I've never needed to. Now, a presta valve is essentially a schrader valve without a spring, so that might be something that you could look into.

Also of note, the last piston I built had a homemade check valve in it about the same size as a schrader. It consisted of a 1/8" compression coupling (the kind used on copper pipe and stuff). A small o-ring was obtained to seat inside it, then an airsoft bb used to create the "check." If this interests you any, I can make a diagram with more detail if needed. Otherwise, I don't know.
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Unread postAuthor: daniel323 » Tue Apr 07, 2009 6:12 pm

i wouldnt mind a diagram....hubb017
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Unread postAuthor: inonickname » Tue Apr 07, 2009 6:30 pm

If you want to remove the spring on a schrader it's simple. Buy some long valve stems, they have the spring on the outside so it is easy to modify or remove.
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