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Caveman simple HiPressure rifle...

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: jeepkahn » Fri Jan 08, 2010 6:43 pm

Ahhh, you thought i was using a bv as the main valve...

On this gun I use a 3/4qev as the main valve and the 1/2bv instead of a combo of 1/4qev/blowgun for the pilot... I was comparing what would pilot the main valve fastest, and IMHO the 1/2bv will actuate the main valve faster than a blowgun would actuate the 1/4qev which would then actuate the main valve... Thats why I was comparing 1/2"bv to a modded blowgun... :D
poland_spud wrote:if a 1/2" BV was superior to 1/4" QEV no one would bother to use them...
if they were using it as a mainvalve on a 3/4" barrel the BV would be better(but on a sub .5" barrel the qev would be better)...

I think for a few minutes there we were talking about different applications...

And I never use tubing or hose between my trigger and pilot valve(too much wasted co2), thats why I'll use a mechanical link on my cannon that will be valved at the shoulder(for compactness), prolly a bullpup coax...
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Unread postAuthor: POLAND_SPUD » Fri Jan 08, 2010 8:13 pm

I was comparing what would pilot the main valve fastest, and IMHO the 1/2bv will actuate the main valve faster than a blowgun would actuate the 1/4qev which would then actuate the main valve...


are we talking about the time between the pull of the trigger and the moment the main valve fires or about opening time and performance ??

lol right now I am pretty much confused myself

I never use tubing or hose
uhmm yeah but 4X2mm tubing has an ID of 2mm.. so 32cm of 4X2 increase pilot volume by about 1ccm

think how many ccm are in a 1/4" T

the point of using tubing is that you could put the piloitng DCV where you want
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Unread postAuthor: jeepkahn » Sat Jan 09, 2010 9:32 am

POLAND_SPUD wrote:are we talking about the time between the pull of the trigger and the moment the main valve fires or about opening time and performance ??
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
THIS, for the win!!!



I never use tubing or hose
uhmm yeah but 4X2mm tubing has an ID of 2mm.. so 32cm of 4X2 increase pilot volume by about 1ccm

think how many ccm are in a 1/4" T Sometimes it's not about how much volume there is, but How fast can the volume escape, BUT using tubing on a small qev DOES make sense for relocating the trigger...



I think we are talking on the same page now, or at least the same chapter...LOL

Honestly, I'm surprised noone else has chimed in with thoughts on this subject...
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Unread postAuthor: Brian the brain » Sat Jan 09, 2010 10:22 am

The delay time between pressing the trigger and the valve popping open does not mean the ammo will travel slower.

I deliberately cause delay in my pistons by making them have small area differential between the piston diameter and the sealing surface.

This ensures the valve only opens after the pilot has almost completely emptied.Apon opening the large sealing face area is exposed, slamming the piston back without the pilot pressure to slow it down.

The actual trouble with BV's is the fact pressure escapes long before the valve reaches full flow, moving the projectile at the minimum flow required to move it, basically.
Therefor bv's are much " slower" as main valves.

You seem to think trigger to valve reaction time is somehow related to projectile accelaration...
It can be, but in the reverse way you think it works.
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Unread postAuthor: POLAND_SPUD » Sat Jan 09, 2010 12:59 pm

I think that a setup with an auxiliary QEV is faster that the one with BV or more less as fast...
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Unread postAuthor: jeepkahn » Sat Jan 09, 2010 2:09 pm

I would lay down in the middle of the rd before I would build a bvmainvalved cannon...

but the point I've been trying to make is, comparing the valves that your finger/hand/bigtoe/etc on , a .5"BV will vent the initial pilot pressure faster than a blowgun hands down, and prolly even a .25"bv will outperform a Blowgun....

When I say a A:BV is faster than a B:qev blowgun combo here is what I'm thinking of:

A:Main Valve=3/4"QEV, pilotvalve= .5"BV

or

B:mainvalve=3/4"QEV, pilotvalve=.25"QEV, pilotvalve pilot=Blowgun


brian the brain wrote:You seem to think trigger to valve reaction time is somehow related to projectile accelaration...
It can be, but in the reverse way you think it works


Actually I don't think that(and without light gas or combustion my projectiles ain't gonna get any faster), I'm shooting for overall performance, which includes Projectile speed, ergonomics, trigger to firing reaction time, aimability, and ease of use... Projectile speed I gots plenty of, it's the other things I'm finetuning now...

And one of these days I may worry about appearances(but for now "pretty is as pretty does" to quote Epoxyman)...
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Unread postAuthor: psycix » Sat Jan 09, 2010 3:06 pm

My 1/2" QEV performed better with a 1/2" ball valve then with a 1/4" QEV + blowgun.
This was tested by firing 16mm marbles over a shooting chrony.

So I would suggest option A.

I believe that even though an 1/4" QEV dumps faster then the 1/2" ball valve, the rapid decompression of the pilot area may "suck" the piston of the 1/4" back closed, potentially bouncing the 1/2 inch's piston on an air buffer. While the ball valve just opens slowly (and not even completely), it stays open, making sure the piston of the 1/2" doesn't bounce.
Also, the slow opening of the ball valve doesn't matter much as the QEV's piston will remain shut anyway. Especially with high-ratio "snapping" pistons this effect will be larger.

EDIT:
I wouldn't focus on valve response time. That will be unnoticeable short anyway.
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Unread postAuthor: POLAND_SPUD » Sat Jan 09, 2010 11:16 pm

yeah this is a really interesting discussion, I wonder who is right

I've just ordered a 1/8" QEV and I going to test the idea myself...
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 10, 2010 2:06 am

psycix wrote:My 1/2" QEV performed better with a 1/2" ball valve then with a 1/4" QEV + blowgun.
This was tested by firing 16mm marbles over a shooting chrony.


Fascinating, do you have the actual data?

And one of these days I may worry about appearances (but for now "pretty is as pretty does" to quote Epoxyman)...


That's the ticket :) of the horrible plumber's nightware that was the Sten submachinegun, some anonymous wit one wrote:

"The Germans learned, as did many others, that a bullet from a Sten was just as lethal as a bullet from something more fancy"


In that spirit, great job, reminds me of my frankenburstdisk I had put together from work fittings :)
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Unread postAuthor: psycix » Sun Jan 10, 2010 1:43 pm

Let me perform a search...

Here you will find the thread I posted some results in.
A second session is on the second page.

30 bar, QEV+blowgun, 270 m/s
40 bar, ball valve, 295 m/s
I didn't post it there but from my memory I recall shots coming out on 275...
This could either be the ball valve on 30 bar or the QEV+blowgun on 40.
In any case, the ball valve (which vents through a the handle and 1/4" quick connect!) performed better on the same pressure level than the QEV+blowgun (which also vented through a quick connect).

EDIT
Make that ball valve on 30 bar.
I think we replaced it because the blowgun wasn't safe on 40.
Maybe that BTB still knows which was what...
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Unread postAuthor: Jack_Hogg » Sun Jan 10, 2010 3:13 pm

Make sure to have a big male quickconnect, there are diffrent types and sizes of male connect's, it will effect the preformance of the piston valve very much.
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Unread postAuthor: psycix » Mon Jan 11, 2010 3:36 pm

Maybe at yours it did because you had a heavy piston, but for me it vents through a 1/4" QC without any problems. And of course you are running a slightly larger caliber, making the QC relatively smaller.
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Unread postAuthor: Major Collins » Mon Jan 11, 2010 10:21 pm

you should replace the ball valve with a blowgun(thats what im planning to do :)) and then it will have a very comfortable stock and trigger .. and i think you called me cave man too .... lol

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Unread postAuthor: MrCrowley » Mon Jan 11, 2010 10:32 pm

Major Collins, I don't think you understand. If you made the pilot valve on both your cannon and jeepkahn's, you will lose performance.
Blow guns have almost no flow, and a ball valve certainly is better. Especially when using 750psi...
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Unread postAuthor: Brian the brain » Wed Jan 13, 2010 5:22 pm

Maybe that BTB still knows which was what...


Huh..???

:D
I'm having trouble remembering wether or not I ...wait...what?

Huh?
:roll:

I do recall you being surprised the performance did not go down..
So..at least I can confirm it wasn't worse..

So yeah..I do believe the ballvalve was better..
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