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QDV as pilot

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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QDV as pilot

Unread postAuthor: daniele tn » Thu Feb 10, 2011 4:28 pm

Hey guys,
as you maybe already know thanks to another post, I am bulding another piston valve gun.
I'm really trying to get the best efficency using off the shelf parts and found an interesting and efficent solution in order to pilot my piston.
The design is based on tech's QDV and is also surprisingly similar.
The only issue I can see is the moving of the piston: I have read that the heavier the projectile the faster the piston will open (makes sense) but what if I don't have a projectile?
How will the valve react?
Thank you
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Unread postAuthor: saefroch » Thu Feb 10, 2011 4:38 pm

The valve will still open considerably quickly without a projectile. Tech has posted videos demonstrating a dry-fire with a QDV.

If I were you, I'd use the QDV as the main valve if you're going to build one anyway.
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QDV Dump

Unread postAuthor: Technician1002 » Thu Feb 10, 2011 8:42 pm

The mass of the air in the barrel is enough back pressure on a QDV to open it as noted above. The video of it is here. Another example is the low pressure indoor shot with no barrel in my using o rings video.


[youtube]http://www.youtube.com/watch?v=RmubzCSv9KU[/youtube]

O ring video with low pressure no barrel dry fire is here;
http://www.youtube.com/watch?v=BbDiZiRVrnk
Fast forward to the 5 minute mark for the dry fire indoors.

My channel is here;
http://www.youtube.com/user/Technician1002
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Unread postAuthor: Gaderelguitarist » Thu Feb 10, 2011 11:26 pm

Ah, Tech. Always with your shameless self promotion :lol:

Daniele, I had a piston valve cannon back in the day that only fired if the barrel was loaded. That was a very poorly built piston valve I will tell you. Have you posted a drawing of your plans on a previous post that I've missed?

I agree with Saefroch on this one. It's similar to building a small piston valve to pilot a sprinkler valve.
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Unread postAuthor: daniele tn » Fri Feb 11, 2011 5:15 am

Good, so using a QDV as pilot can be done.
On the other hand I understood that it would be better to use it as primary valve, but I could have some problems, due to the fact that I am restricted to off-the-shelf parts and a dremel, not to mention also design issues and the ability to have bolt or camlock loading (anyway an efficient loading system regarding efficiency and space usage) and interchangeable barrels.
Anyway, if I can find a way to have a QDV and all the other requirement I will certainly opt for the QDV.

In the meanwhile do you have any suggestion regarding pilot valves?
I need a pilot that must be easy and comfortable to use (like a conventional style trigger) be quite efficient and withstand 30-40 bar of pressure.

Thank you
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Unread postAuthor: FighterAce » Fri Feb 11, 2011 6:08 am

I use a schrader as the pilot... this is my hammer for it

Image

Check this thread for more info

And the earlier version here on spudfiles
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Unread postAuthor: POLAND_SPUD » Fri Feb 11, 2011 12:40 pm

Ah, Tech. Always with your shameless self promotion
lol dude WTF are you talking about.... tech and self promotion ? naaahhh.....
:D
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Unread postAuthor: daniele tn » Fri Feb 11, 2011 3:49 pm

FighterAce wrote:I use a schrader as the pilot... this is my hammer for it

Image

Check this thread for more info

And the earlier version here on spudfiles


I really like it, I may be going with a design similar to yours...
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Unread postAuthor: saefroch » Fri Feb 11, 2011 4:05 pm

daniele tn wrote:Good, so using a QDV as pilot can be done.
On the other hand I understood that it would be better to use it as primary valve, but I could have some problems, due to the fact that I am restricted to off-the-shelf parts and a dremel, not to mention also design issues and the ability to have bolt or camlock loading (anyway an efficient loading system regarding efficiency and space usage) and interchangeable barrels.
Anyway, if I can find a way to have a QDV and all the other requirement I will certainly opt for the QDV.
I'm confused here. If you're planning to build a QDV in the first place, why not use it as the main valve?
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Unread postAuthor: Gaderelguitarist » Fri Feb 11, 2011 5:43 pm

I'm confused here. If you're planning to build a QDV in the first place, why not use it as the main valve?


I think he just wants to have an efficient pilot valve for his piston. The QDV probably struck him as a good idea.
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Unread postAuthor: daniele tn » Sat Feb 12, 2011 5:20 am

Gaderelguitarist wrote:
I'm confused here. If you're planning to build a QDV in the first place, why not use it as the main valve?


I think he just wants to have an efficient pilot valve for his piston. The QDV probably struck him as a good idea.


That's right.
I would like to use a QDV as primary valve, but I cannot (or it will be really difficult) because I don't have a lathe or drillpress to turn a decent piston.
I also cannot use a coaxial because I need my gun to have detachable barrel and bolt action loading.
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Unread postAuthor: FighterAce » Sat Feb 12, 2011 6:02 am

I know a guy that made a QDV with nothing more then a copper T fitting and couple of connectors on either end. For the piston, some all thread, washers and thick rubber gaskets. You dont need a drill press or a lathe... or soldering equipment... I'm sure it could be done with threaded brass fittings.
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Unread postAuthor: daniele tn » Sat Feb 12, 2011 7:17 am

FighterAce wrote:I know a guy that made a QDV with nothing more then a copper T fitting and couple of connectors on either end. For the piston, some all thread, washers and thick rubber gaskets. You dont need a drill press or a lathe... or soldering equipment... I'm sure it could be done with threaded brass fittings.


I saw the video of the very same guy and gun (is it airgunman?) and I have to say that it is possible, but using threaded fittings (and still having bolt action) dead space wuold be an issue and would eliminate the advantages of having a QDV.
That said, I am evaluating every possible solution (right now I was playing with different fitting to have an idea...)


Anyway, I have a question:
I know that in piston valves the efficent piston movement would be d/2 what about non coaxial QDV? (see video for a non coaxial QDV [youtube]http://www.youtube.com/watch?v=FsRl05rtWt0[/youtube]
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Unread postAuthor: FighterAce » Sat Feb 12, 2011 7:54 am

Yes thats him :D

I think the D2 rule doesnt count here.... because theres no limit to pilot volume... since there isnt any. The more the piston moves, the less obstructions the air will encounter.... at least I think its like that.
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Unread postAuthor: Crna Legija » Sat Feb 12, 2011 8:54 am

im pretty sure is d4 and as FighterAce said there is no rule because there no pilot volume
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