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shut-off valve suppressor

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Unread postAuthor: POLAND_SPUD » Tue Feb 28, 2012 5:59 pm

Image
the heavy steel bearing wasn't picked up by the gasses...
damn can't you see the port is above the bb ?? don't you think it would work better if it was BELOW it ?
:D
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 29, 2012 12:25 am

LOL

:P

Don't forget the BB is in a groove, not a tube, so there's plenty of space for the air to get around it ;)
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Unread postAuthor: POLAND_SPUD » Wed Feb 29, 2012 6:57 am

Don't forget the BB is in a groove, not a tube, so there's plenty of space for the air to get around it
still you could have put more effort into it... now that you have a lathe you can basically cut a few holes in a block of acrylic and your done
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Unread postAuthor: jhalek90 » Wed Apr 25, 2012 3:26 pm

My worry is that it would not be picked up by the gasses at all.


maybe i don't quite understand the physics, but is this not exactly how cloud BBMGs work?

i suppose cloud chambers have more time to allow the air to act on the BB... but the concept is the same right? Bernoulli principle?
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 25, 2012 8:05 pm

jhalek90 wrote:maybe i don't quite understand the physics, but is this not exactly how cloud BBMGs work?


Yes, pretty much - and BB weight is important for clouds too.

It's much easier to make an airsoft BBMG work reliably because of the light weight of the projectiles means they're more readily picked up even by small flows and pressures.
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 02, 2012 3:26 am

What do you know, this wasn't a new idea.

Can't find much detail though, other than that it was developed around 1898 by a certain French Colonel Humbert.

The design makes it a lot easier for the ball to block the muzzle, but the obvious problem with the ball on a ramp is that if you try to shoot at a downward angle...

Some pics taken from this article, it seems that there was a variation with a flap instead of a ball.
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Unread postAuthor: ramses » Sun Sep 02, 2012 10:07 am

What I don't like about that design is that if you fire the gun upside down (could happen), you shoot off the end of your barrel.

Also, they vent combustion gas right back at the operator
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 02, 2012 10:41 am

ramses wrote:What I don't like about that design is that if you fire the gun upside down (could happen), you shoot off the end of your barrel.


Even if you point it at a slight downward angle as I mentioned.

Also, they vent combustion gas right back at the operator


True, though given the small bore of the vents it would probably not be that much of an issue.

Anyway, decided to give this another go. My previous efforts floundered because I made them too weak, and because I only had airsoft BBs which were just 0.5mm greater in diameter that the 0.22" pellets I was using.

This time round, I used the aluminium tube and hammer-fit epoxied delrin endcap construction that has served me well with high mix hybrids. I also have a selection of plastic bead sizes (7.59mm, 7.88mm and 8.10mm) to choose a blocker from. The centre bore should allow the barrel gasses to leak out, though if that's still too loud I'll block it up. Blowing through the thing easily lifts the beads to block the muzzle, my fear again is that it will strike the pellet on the way up.

I put a female 1/2" UNF thread on the back to be able to attach it to my Daystate for testing, now that it's in my commercial interest to make a compact and effective airgun silencer :) watch this space.
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Unread postAuthor: Fnord » Sun Sep 02, 2012 12:41 pm

The problem I can see is what happens when your projectiles are approaching the SOS in normal air.

These shut-off suppressors work by sucking the ball/flap into a stream of fast moving air, but when your projectile is traveling at sufficient velocity, there is also a similar pressure wave building up in front of it. This will not likely close the valve completely before the projectile gets there, but they may bump into each other a bit, quickly becoming a source of mechanical wear.

This is another reason why my old 'shunt' valve design was to use a controlled amount of contact between the projectile and flap to shut itself.
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 02, 2012 1:31 pm

I just tried it out with the Daystate with the power turned up (900 or so fps) and no luck, all sizes of bead didn't budge. I'm guessing having the ball between two disks leaves too much volume for the venturi effect to kick in from the brief blast of air....

They seal well enough when I blow through it, but then again breath is low pressure but high volume.
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Unread postAuthor: Lockednloaded » Sun Sep 02, 2012 2:32 pm

jackssmirkingrevenge wrote:They seal well enough when I blow through it, but then again breath is low pressure but high volume.


So in theory, this should work for the conventional "low pressure-high volume" spudguns?
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 02, 2012 4:03 pm

Lockednloaded wrote:So in theory, this should work for the conventional "low pressure-high volume" spudguns?


I modded it with a single vertical bore and the ball now seems to be jumping to block the port, but no difference in noise. It would appear that the delay between pellet passage and ball movement is sufficient to allow the bulk of the air to escape.

I would surmise this is the reason why the concept is not in general use. Looks great on paper, but does not translate in practice.
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Unread postAuthor: POLAND_SPUD » Sun Sep 02, 2012 5:26 pm

So in theory, this should work for the conventional "low pressure-high volume" spudguns
but then again conventional low pressure high volume spudguns are just poorely designed spudguns ;-)

One can get better performance from high pressure low volume guns and keep them quiter at the same time
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Unread postAuthor: PotatoEnemy17 » Sun Sep 02, 2012 5:45 pm

But if you get the proper chamber to barrel ratio then the noise should be minimal any way, right? :?
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Unread postAuthor: POLAND_SPUD » Sun Sep 02, 2012 6:15 pm

But if you get the proper chamber to barrel ratio then the noise should be minimal any way, right?
yes, but such a design will have less power than a gun with a larger chamber

However by using higher pressure at lower volume one can get more power than using high volume at lower pressure

for example -> 10 L of air at 2 bar = 2 litres of air at 10 bar as far as total volume of air is conecerned but you'd get higher muzzle velocity from a 2 L chamber at 10 bar than the other way round


By reducing chamber volume by a factor of two and increasing pressure twofold you get higher muzzle velocity while total volume and pressure of air as it leaves the barrel is the same... so you can design a quiet gun (thx to favourable chamber barrel ratio) and it can be powerful (since you're getting free power by increasing pressure&reducing volume)


damn that was a lenghty response
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