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Semi-Auto Valve

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Semi-Auto Valve

Unread postAuthor: qwerty » Sat Feb 27, 2010 10:42 am

For an upcoming semi-auto gun i need a valve that opens and closes very fast at one pull of the trigger but enough to pilot a 15mm piston valve.

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Unread postAuthor: Crna Legija » Sat Feb 27, 2010 11:03 am

A hammer valve with a nail gun hammer or mabe qev with solenoid valve pilot
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Unread postAuthor: qwerty » Sat Feb 27, 2010 12:19 pm

Nah it would be to bulky for my kind of gun. I'm thinking poppet valve but i'm not sure.
How it works? well basicly there is a big chamber then a 1-way valve leading into a coax piston setup. Fill the gun up pull the valve pilots the piston then the air coming back into the piston setup reseals the piston.
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Unread postAuthor: POLAND_SPUD » Sat Feb 27, 2010 12:38 pm

I don't think it is possible to have a 1 way valve... 'ways' mean the number of ports so, for example, a ball valve is a 2 way valve

I know what you are looking for but it won't be easy.... I suppose you could achieve what you want with a NO closed 3 way valve that would vent pilot side to a small sealed chamber once actuated and then that air would be released to atmosphere once you depress the valve

that's not an ideal solution as it requires you to have a small chamebr just in order to keep vented air

poppet valve but I'm not sure.
How it works?


poppet valves are not balanced so they might not be ideal for high pressure guns





here

Poppets are often just small rubber disks not what you could see above...


EDIT
read this too... it explains the differences between poppet and spool valves as well as a couple of other things (plus it has better pics)

EDIT no 2
ohh god this is the source I mentioned in johnbunsenburner's thread (all in one valve) it discusses metal-to-metal seals
(in other words - no seals per se)
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 27, 2010 1:09 pm

With a properly made piston (good piston fit, maybe o-ringed to make sure, and small pilot volume) even a schrader will be more than adequate. In the past I've used a schrader to pilot pistons as big as 25mm without the benefit of seals, just a tight fit.
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Unread postAuthor: POLAND_SPUD » Sat Feb 27, 2010 1:26 pm

@JSR
I think he wants to achieve a similar effect that you get when using hammer valves as the main valve.... so in other words he wants to use just a small fraction of air from the chamebr for each shot
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Unread postAuthor: qwerty » Sat Feb 27, 2010 3:06 pm

I don't think it is possible to have a 1 way valve... 'ways' mean the number of ports so, for example, a ball valve is a 2 way valve


Sorry i meant a check valve but couldn't think of the word

What about a normal coax piloted with a schrader but using a cap gun as a hammer. Would it reseal?
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 27, 2010 3:07 pm

qwerty wrote:What about a normal coax piloted with a schrader but using a cap gun as a hammer. Would it reseal?


If Brian's experiments are anything to go by, that should be the case.
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Unread postAuthor: POLAND_SPUD » Sat Feb 27, 2010 3:21 pm

the important question is what you want to build...

if you compare what BTB built and what I used on the MKIII (3 way valve + QEV) air consumption is comparable...
so it's more a matter of personal preference

For me it's ok to have an external tank to store air as I want a lot of shots. There is no way I could store enough air needed for 15 or more shots in the main chamber...

but if you want a self contained launcher that can fire a couple of shots then the design that BTB used is better
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Unread postAuthor: qwerty » Sun Feb 28, 2010 4:44 am

Sorry BTB has made so many guns i'm not sure which one uses my idea, is it his big rifle or.....Could someone link me please. :?
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Unread postAuthor: jackssmirkingrevenge » Sun Feb 28, 2010 4:58 am

I can link you to my attempt with a schrader pilot, it worked well at compressor pressures but not with HPA, though I put this down to poor piston design (solid rubber as opposed to my usual casting) because the theory is sound.

Image

[youtube]http://youtube.com/watch?v=xKq4ktpplMA[/youtube]
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Unread postAuthor: qwerty » Sun Feb 28, 2010 8:37 am

Ok, but whats with the Two shraders?
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Unread postAuthor: jackssmirkingrevenge » Sun Feb 28, 2010 8:42 am

The non-pilot schrader has the core removed, it's simply there as a connection.
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Unread postAuthor: POLAND_SPUD » Sun Feb 28, 2010 8:43 am

he used the one to the left to pressurise the gun (from chamber side) the one on the right is for piloting...

though keep in mind that you need a valve with higher flow... and one that opens in a consistent manner (otherwise the gun might not be accurate)
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