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Unread postAuthor: psycix » Mon Apr 06, 2009 12:02 pm

So you are not sealing down the mag while firing? Simply gravity feeding stuff down a T piece again?

I think I am making things too complicated for myself. Just bought two tiny brass pipes from the RC store, 10 euro's each.. blah..
But I will build that BFWB. :D
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 06, 2009 12:25 pm

psycix wrote:So you are not sealing down the mag while firing? Simply gravity feeding stuff down a T piece again?


Why not try the simplest option first? It's a relatively small and sealed mag so it shouldn't affect performance much, we'll see tomorrow when the epoxy's cured ;)
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Unread postAuthor: Gippeto » Mon Apr 06, 2009 1:22 pm

Yes Jack, that valve will work perfectly. :)

Of course there is this little wrinkle yet to be straightened out;

We use BSP here in Europe though, not NPT... hmmmm.


Perhaps all paintball "stuff" is npt, even in Europe?
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 06, 2009 1:26 pm

Gippeto wrote:Perhaps all paintball "stuff" is npt, even in Europe?


Valve ordered, as to the thread type niggle there areBSP/NPT adapters so I should be fine.
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Unread postAuthor: Dave_424 » Mon Apr 06, 2009 2:29 pm

hey, I have the same paintball HPA tank and the threads are compatable with 1/2" BSP fittings

Found out today by screwing it into a 1/2" QEV:P

hope this helps

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Unread postAuthor: jackssmirkingrevenge » Mon Apr 06, 2009 2:37 pm

Dave_424 wrote:hey, I have the same paintball HPA tank and the threads are compatable with 1/2" BSP fittings


That would be perfect :) it'll be a couple of weeks before I get the tank though, we'll see when it gets here. In the meantime the hopper I made for the valve that is the subject of this thread is curing, hope it works as I'm keen to do a couple of 100+ round videos :D it might need a spring plunger like inline BBMGs to work reliably, all research and development will be shared in due course.

Methinks those QEVs you bought are going to be put to very good use :D
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Unread postAuthor: Dave_424 » Mon Apr 06, 2009 2:59 pm

haha you can read my mind :)

One is going to pilot my 3/4" QEV because the blowgun just isn't quick enough

and there is a possibility to go HPA semi auto for another one

all other ones will be sold

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Unread postAuthor: jackssmirkingrevenge » Tue Apr 07, 2009 12:32 pm

Here it is with the hopper and BBs as ammo, not 100% reliable but good enough. Note how the rate of fire decreases progressively as the pressure in the compressor goes down. Target was a plastic box.

[youtube]http://www.youtube.com/watch?v=hXM-bPOtJGU&feature=channel[/youtube]


Here's the hopper and valve firing:

[youtube]http://www.youtube.com/watch?v=U_1cN7lhW5c[/youtube]


Unfortunately with the smaller calibre power is down from what it had been with pellets, here's what happened with the 0.5mm aluminium plate, most rounds failed to penetrate it - no video though, too many BBs flying back at my face :roll: but with 450-850 psi on tap eventually it should be a blast, literally :D
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Unread postAuthor: SPG » Tue Apr 07, 2009 12:52 pm

Is it the smaller calibre or the massively increased dead space created by the hopper? It only occured to me today that with no bolt that's basically what you've got.
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Unread postAuthor: psycix » Tue Apr 07, 2009 1:46 pm

Is that a bottle on a T-piece? And it doesnt double feed like hell?
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 07, 2009 11:59 pm

SPG wrote:Is it the smaller calibre or the massively increased dead space created by the hopper? It only occured to me today that with no bolt that's basically what you've got.


The dead space doesn't help but it's the calibre that makes the major difference. For a high pressure version I would go for a barrel material tube that's spring loaded rather than a hopper feeding into the tee, you can fit 100 BBs in just 45cm and that would be sufficient for me.

Is that a bottle on a T-piece? And it doesnt double feed like hell?


Yes it is, and no it doesn't, because of the way it's designed:

Image

With each blast of air, the BB in the breech goes out of the barrel while the rest are pushed up the magazine tube.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 08, 2009 11:03 pm

Fnord wrote:isn't as easy as it looked


I wouldn't have been working on it for years if it was ;)

What I'd like to know is any internal dimensions you can give me on your valve; seat diam, piston diam, est. dead space, chamber volume, and also does your piston cover the "out" port initially, and only vent once it has moved a little?
I think you somehow hit a sweet spot with the dimensions you used that doesn't necessarily work with similar designs, so I'd like to have a shot at "cracking the code" so to speak.


It is important the that piston doesn't obstruct the outlet when it's closed, otherwise when returning from the first cycle it will encounter pressure and "hang" - In my design (the second one is essentially the same aside from the substitution of the air spring with a coil spring) I avoided this.

In terms of dimensions I had already mentioned two critical factors earlier in the thread:

1) The piston seat must be significantly bigger than the outlet to the barrel, to ensure that the piston chamber fills with pressure faster than it can empty and the piston has time to actually pop

2) The piston must be significantly wider than the piston seat, in order for there to be enough area for the pressure to act on and overcome the spring strength.

I attached a diagram of the sprung design with the relevant dimensions to give you an idea.

The other two relevant factors are spring strength and rate of flow into the chamber. The spring setup I'm currently using will pop at around 80 psi, and my compressor starts out at 110 psi. Flow into the chamber is also important to establish reliable functioning and rate of fire. I adjust this using the flow control knob on my compressor, in this case it is a question of finding the "sweet spot" for a given pressure and spring strength.

Also, I liked your plastic box/bb hopper video. Must have been very satisfying to ventilate something so thoroughly in full auto.


Can't quite describe it :) I was in a hurry when I did it though and didn't realise what had happened to the barrel, see attached pic! No idea why or how, I'm thinking barrel jam or loose rolling BB struck by another projectile.

Near the end it reminded me of an old lady pedaling up a steep hill and losing momentum :D

Maybe a bigger compressor tank is in order?


I have a 3,000 psi paintball tank on order, regged to 450-850 psi it should give a constant rate of fire and a teeny bit more power, expect a submachinegun of sorts from yours truly after the tank arrives from your delightful nation :)
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Unread postAuthor: Pyro Ninja » Thu Apr 09, 2009 2:05 am

Indeed "WTF?!?!" haha
How strange. Well I love the simplicity of your design, I may have to make something similar for one of my future projects :)
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Unread postAuthor: SubsonicSpud » Thu Apr 09, 2009 2:51 am

This is one excellent design JSR, seems very efficient, Congratulations. I have to say I might try making a large high pressure one for a marble sized gun, definitely has a nice rate of fire. I can't get my hammer valve repeater to slow down enough for my use, and i don't want to be bleeding buckets of air like a popoff repeater. You're valve seems like a perfect solution to the problem :P

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Unread postAuthor: Carlman » Thu Apr 09, 2009 3:54 am

now thats a keeper mate! love the 'bulge'

and no im not talking about your boyfriend...
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