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Balanced Spool Valve Design

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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Balanced Spool Valve Design

Unread postAuthor: boyntonstu » Sat Jan 08, 2011 12:45 pm

[youtube]http://www.youtube.com/watch?v=FsRl05rtWt0[/youtube]

Simple, effective, cool.

Would a cross and 2 short chambers be better for flow than a T?
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Unread postAuthor: Technician1002 » Sat Jan 08, 2011 1:25 pm

It looks like a cross between a toolie valve and a QDV. Shorten the gap in the middle and make a short one piece spool and it will end up as a QDV.

Are you doing anything to prevent lifting the front o ring as it comes out of the barrel into the T. An early design of mine with a gap like that instead of ports in a pipe had a bad habit of shooting the front o ring as it lifted out of the groove when fired.

I have not worked on it for quite a while. I am building a 1/2 inch coaxial copper QDV with a 1 inch chamber.

A cross would flow better than a T. Even better flow is with a coaxial chamber.

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Unread postAuthor: boyntonstu » Sat Jan 08, 2011 1:37 pm

Technician1002 wrote:It looks like a cross between a toolie valve and a QDV. Shorten the gap in the middle and make a short one piece spool and it will end up as a QDV.

Are you doing anything to prevent lifting the front o ring as it comes out of the barrel into the T. An early design of mine with a gap like that instead of ports in a pipe had a bad habit of shooting the front o ring as it lifted out of the groove when fired.

I have not worked on it for quite a while. I am building a 1/2 inch coaxial copper QDV with a 1 inch chamber.

A cross would flow better than a T. Even better flow is with a coaxial chamber.

Click to see full size.
Image



It's THEAIRGUNMAN's design and not mine.

There is no groove:

http://www.airgununiverse.net/community ... 434.0.html
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Unread postAuthor: Technician1002 » Sat Jan 08, 2011 2:21 pm

Nice design on the air seal. From your video it seems to work well. That would solve the problem with o rings blowing out of the groove.
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Unread postAuthor: boyntonstu » Wed Jan 12, 2011 10:21 pm

[youtube]http://www.youtube.com/watch?v=UWKWrAfN4tU&feature=sub[/youtube]

[youtube]http://www.youtube.com/watch?v=4i7v4Q9dSl4&feature=sub[/youtube]

Test shot with spool valve.

His piston will become a bolt!

Very creative and instructive.
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Unread postAuthor: POLAND_SPUD » Wed Jan 12, 2011 11:08 pm

His piston will become a bolt!
yeah, I like that
Though it is a bit tricky as the piston/bolt stroke has to be long enough

I think I know how to build the trigger:
use a steel wire/cable (essentially just bicycle cable brakes) to open the valve... when the valve opens the piston should be forced backward by the pressure...
put a spring behind the piston that so that it can reset it
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Unread postAuthor: nature-boy » Thu Jan 13, 2011 3:41 am

POLAND_SPUD wrote:use a steel wire/cable (essentially just bicycle cable brakes) to open the valve...
...put a spring behind the piston that so that it can reset it


That's exactly what I tried last week, only thing I used strong fishing line instead of cable and a O-ringed, short and light piston out of alu pipe epoxied together. I planned on just attaching the fishing line to a simple trigger, but the problem was, that it was kind of hard to pull under pressure (like it seems in your/airgunmans videos boyntonstu), without pressure it was really easy to move the piston. I think this was because the O-rings deformed under pressure...
But the big fail of the gun, (I'm still disappointed) was the fact that I build a restriction out of a short piece of a nail, which I glued trough the pipe in front of the piston, the prevent it from going too far, when it is reseted.
Finally the restriction nail broke off, and now I have a small hole in front of the ports, what makes the gun useless. :( still thinking about how I can fix it because it seemed so promising and I had really nice ports...
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Attachments
IMG_0326.JPG
here you can see the four ports and the (stupid) nail epoxied into the barrel wall...
IMG_0331.JPG
the actual gun, the barrel with ports is epoxied into the T.
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Unread postAuthor: POLAND_SPUD » Thu Jan 13, 2011 4:11 am

still thinking about how I can fix it because it seemed so promising and I had really nice ports
hmmm MOAR epoxy ?

though don't forget that while epoxy is quite useful... but if something breaks, you're fu....
lol trust me I've been there

That's one of the reason why I prefer threaded fittings - you can dissemble, assemble again, service and/or modify such a gun in just a couple of minutes

that it was kind of hard to pull under pressure
you can use that effect to build a sort of compression fitting that keeps the barrel in place

you just need a T with male threads, some orings/rubber washers that fit tightly around the barrel and some fittings with female ports... the seals go between male threads of the T and the fittings.. as you tighten them the seals expand and keep the barrel locked in place

Just make sure it holds well
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Unread postAuthor: Technician1002 » Thu Jan 13, 2011 12:08 pm

I have noticed that things do tighten up some as o rings hold pressure. With care, making the walls of the grooves vertical instead of on a slant helps as well as a good polish of the surfaces the rings have to slide on.

This good polish is what enables my grandson to be able to fire the Marshmallow Cannon at 100 PSI.

This tightening of the o rings is one of the reasons I am working on a 2.5 inch cannon before building the 3 or 4 inch versions. I'm going to be doing some design experiments so when I build the larger versions, they can be fired at high pressure.

Some people have some difficulty firing my 2 inch at 100 PSI due to the tightening of the o rings.

It can be seen in one of my launch videos where I tell the guy to pull hard. His first pull did not fire it.
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