"Vacuum Barrels" aka "Dry Barrels"

[Cammo]

Hi Tromic,
I was really wondering if the cyrano was submerged and THEN pointed up underwater to let the air out that would be trapped in the barrel when loading it out of water? I think the wet barrel system was still acting like a dry barrel due to trapped air, but like you say above maybe it was the other way around.

Hopefully we can get some evidence of the Omer airbalete up here, my friend just got and thinks it is pretty hot:martialHe says he shot a few kg samson fish from 5m with it, so that sounds pretty good. A friend who also owns 2 pneumatics (Mongrel on this site) also thinks its pretty good, not cheap however. :friday
We have been thinking about how to measure the performance off all these guns under similar conditions. It is hard to say fire then at the same time, I know you suggest videoing and then slowing it down to try and measure shaft speed?
Cheers, :blackeye

 

[tromic]

Hi Tromic,
I was really wondering if the cyrano was submerged and THEN pointed up underwater to let the air out that would be trapped in the barrel when loading it out of water? I think the wet barrel system was still acting like a dry barrel due to trapped air, but like you say above maybe it was the other way around.

Hopefully we can get some evidence of the Omer airbalete up here, my friend just got and thinks it is pretty hot:martialHe says he shot a few kg samson fish from 5m with it, so that sounds pretty good. A friend who also owns 2 pneumatics (Mongrel on this site) also thinks its pretty good, not cheap however. :friday
We have been thinking about how to measure the performance off all these guns under similar conditions. It is hard to say fire then at the same time, I know you suggest videoing and then slowing it down to try and measure shaft speed?
Cheers, :blackeye

Hi Cammo,
After testing my Cyrano with 6,5 mm shaft I do believe that Omer airbalete could be very good because it is using 6,75 mm shaft and 11,2 mm piston. This is enough to be visible better in performance than Cyrano with 7 mm shaft and 11 mm piston.
Cheers

 

[Crispin]

Adding some pics of my tovarich here instead of hijacking the loading thread:

Thanks to Ramon @ kara-yo for the Tovarich kit & trigger kit, and Dave @ spearo for the spears, what used to be a very mediocre pneumatic is now an underwater cannon.

 

[tromic]

All the tests were done with Cyrano 850 at 20 bars at 2 wraps distance (3,5 m).

This was the tool for comparing.
When I shoot the gun, the shaft pulls the line and the line pulls the left side of the rubber tubing. The right side of the tubing is tied to the gun. When the tubing is expanding it pulls the sliding knot along the yellow line, which indicate the max pulling force.

Factory, water barrel. This was a reference.

Tomba results. Comapring to factory (water barrel) tomba (tubing version) is 19 % better in energy.


Mamba results. Comapring to factory (water barrel) mamba is 26 % better in energy.

Tomba with O-ring and 6,5 mm tahitian spear and the "spring slider". 48 % better then factory, water barrel, and 7 mm shaft.

Tomba with O ring and 6,5 mm tahitian spear and the spectra to keep the shaft. The same configuration as above but with the spectra instead of the "spring slider". This was very poor in performance. Factory gun - wet barrel, almost 110% better in energy at 3,5 m distance. The most important is to make the drag as low as possible.

I have tried this this type of slider too, to make the drag lower - "knot slider". Very good performance. The result at the scale was more than 20, as with "spring slider", 48 % better than the factory gun - wet barrel.

 

[tromic]

well, I was expecting more comments. 25% better performance with vacuum barrel to water barrel, if vacuum barrel system is working fine.
Is it OK, acceptable? In best case, everything fine tuned, up to more than 50% better to stock (water barrel) gun.

 

[Cammo]

Hello Tromic!
I actually didnt see your post or would have made a comment.
Call me slow, ok, call me very slow, but I don't know how you measured the force put out by each gun?
Can you explain this a bit more to slow me?

Also your conclusions - you said the tomba with 6.5mm was the best, I guess this is because you can only run a 7mm in your mamba? (as you said the Mamba was actually gave the biggest increase).

I now own a 1250x9mm Blacksea hydropneumatic and with a LOT of help from PopgunPete have got it together and will hopefully do some posts soon, it looks badass :martial
I did a pool test today and just shot a bit of water in the air....when I get some spears knocked up I will do some real tests.

Attached is my preference in line slides - the metal one! It is a lot smaller in diameter than the plastic ones which I seem to break and lose the shaft. They are also a lot easier to pass it through a fish to thread it off the line.
Cheers

 

[tromic]

Cammo, please look at this: http://forums.deeperblue.com/pneumatic-spearguns/81791-tomba-all-one-barrel-sealing-5.html
Maybe it would be more clear. If not, ask again, please. I thought it was clear.

 

[Cammo]

Hey Tromic,
I read that then, but I still don't see how you measured the force?
cheers :blackeye

 

[tromic]

Hey Tromic,
I read that then, but I still don't see how you measured the force?
cheers :blackeye

I will try to be more clear. When I shoot the gun, the shaft pulls the line and the line pulls the left side of the rubber tubing. The right side of the tubing is tied to the gun. When the tubing is expanding it pulls the sliding knot along the yellow line, which indicate the max pulling force. I suppose this helped a little.

 

[Cammo]

Hey Tromic,
I see the system, quite ingenious! Seeing results are so closely grouped together, I would guess it is quite accurate as well. I will post some nice pics of my new speargun soon:friday

 

[tromic]

Hey Tromic,
I see the system, quite ingenious! Seeing results are so closely grouped together, I would guess it is quite accurate as well. I will post some nice pics of my new speargun soon:friday

Happy you see it. It seems to be very useful and accurate. I am waiting to see your new gun pictures.:friday

 

[tromic]

Here is the discussion about the influence of depth to "Vacuum barrel" aka "Water barrel" gun:

Originally Posted by popgun pete
...
So if the gun had 20 atmospheres in it (20 Bar) then at 40 metres of depth it would be shooting as if it only had 16 Bar in it, at 30 metres down it would be 17 Bar.
...
The Mamba type system is less affected by increasing ambient pressure as the pressure only acts on the spear diameter, not the piston diameter, which is the same as the inner barrel diameter.
...

If we had 6,5 mm shaft and 11 mm barrel than cross section of the shaft to cross section of the barrel is
(6.5^2) / (11^2) = 0.35.

For dry barrel system gun at 40 meters of depth it would be shooting as if it only had
20 - 4 * 0.35 = 20 - 1.4 = 18.6 Bar in it.

This would be true only if there would not be vacuum in the barrel but just muzzle sealing (what is actually difficult to take separate).
Because of vacuum in the barrel one should add an average pressure of about 0.95 *(1 - 0.35) Bar for any depth,
so the correct answer is

20 - 4 * 0.35 + 0.95 * (1 - 0.35) = 19.21 bar for the depth of 40 m.

For 30 m depth the result would be 19.6 Bar.

What is important to remember is that vacuum barrel performs like there is -1 Bar pressure at the vacuum side of the piston after loading the gun. The average pressure, which actually accelerate the shaft, due to the vacuum, is less than 1 Bar and is about 0.95 *(1 - 0.35) Bar, taken to the high pressure side of the piston, in case the residual volume of air before loading the gun is about 1 % of barrel volume. This was the case for 6.5 mm shaft and 11 mm barrel.

For the 7 mm shaft and 11 mm barrel as Cyrano has, the total advantage at 30 m depth, of vacuum barrel over the water barrel gun is about 42 % for the same gun, same shaft, same slider, and same line. I skipped the calculations not to bother the readers.
It is as if the water barrel Cyrano, at 30 m depth, would be at 29 Bar instead of 20 Bar.

 

[Mark Lamont]

Hi Pete,
So then the question of the 6 mm shaft is only can one load the shaft in the gun? That seems easier in my opinion. I have been using a system of balls on a heavy monofiliment line for years. I set my cocking stock about half way along the guns length and place the spear tip into a drilled hole in the last ball and then hand over hand pull each successive ball into the muzzle a foot or so at a time.
It's nice and safe too.
Mark
My personal preference is a 5/16s shaft but to each there own.

 

[popgun pete]

Hi Pete,
So then the question of the 6 mm shaft is only can one load the shaft in the gun? That seems easier in my opinion. I have been using a system of balls on a heavy monofiliment line for years. I set my caulking stock about half way along the guns length and place the spear tip into a drilled hole in the last ball and then hand over hand pull each successive ball into the muzzle a foot or so at a time.
It's nice and safe too.
Mark
My personal preference is a 5/16s shaft but to each there own.

Hi Mark, I remember reading about your design efforts at Scubapro over the years, you have quite a list of innovative products to your name! Smaller diameter shafts pose a bending problem if the shaft is relatively long and the gun is using high pressure air as it is all too easy to pull down on a loading bar while not working directly in line with the inner barrel bore during a big muzzle loading effort. That can bend the spear, depending on what material it is made from and at 6 mm diameter or 1/4" a shaft is getting pretty thin for muzzle loading. The vacuum barrel kits improve the efficiency of the pneumatic speargun, so you can obtain similar shaft speed results with less air pressure in the gun and thus a lower level of force to overcome during muzzle loading of the gun. Less force means less likelihood of bending the shaft. The efficiency improvement will depend on how restricted the wet barrel operation of the gun was originally, bearing in mind that muzzle relief ports are much larger on modern pneumatic spearguns like the "Cyrano" than they were on the original "Sten". Loading aids that keep the shaft directly on-axis during the loading effort allow slimmer shafts to be used, but the other consideration is what may be imposing bending loads at the other end of the shaft's flight. For years the standard pneumatic speargun shaft size was 8 mm or 5/16" diameter, the guns then being designed as general purpose weapons for mainly reef style hunting.

 

[foxfish]

Hi Mark, can you post a picture of your ball system?

 

[Mark Lamont]

Not to metion the danger of having your shooting line hang up with the trailing end of the spear near or part way out of the inner tube. The trailing end of the spear would fit nicely in one's eye.

 

[Don Paul]

Hi Mark, can you post a picture of your ball system?

I have a fussy mental image of Mark's system but no down loadable way
to plug in to the image bank.

We were on a quest to invent new tricks every week and test them at the off shore islands. I still use a Rubber Maid dive box system with cordage loops to keep all my gear readily assessable and tightly contained on deck.
I copied the idea from Mark almost thirty years ago.

His gun was a true Blue Water tool and as he say's in another thread would lodge the Wally Potts hand made '' Ice Pick'' slip tip deep into many large speedy pelagic fish game fish.
Cheers, Don

 

[popgun pete]

Not to metion the danger of having your shooting line hang up with the trailing end of the spear near or part way out of the inner tube. The trailing end of the spear would fit nicely in one's eye.

I have had a spear come back at me when the fixed loop on the shooting line using a front tied spear and tethered line slide (finned stabilizer) arrangement caught the forward post on the Russian gun that I was using and had just enough give in the nylon line to let the spear tail exit the muzzle for a short distance and then swing the shaft back. The spear slewed sideways in an instant and came flying back, dropping just past the muzzle as it ran out of steam. I later discovered, once I regained my composure, that the line slide had pulled off the spear tail, there being no stop diameter on the shaft tail, allowing just enough line for the shaft to get some speed up before commencing its return journey to the new target which was holding the gun. So I am very wary of snagging hazards on the muzzles of pneumatic spearguns. Using a loading bar there is always a possibility that the loader may break or the spear tip could push through it, but at least you are not relying on the strength of a line to keep the shaft under control.

One of the few pneumatic guns that I know of that uses a slim shaft option is the Russian "Taimen", the smallest shaft diameter being 6.5 mm. They are relatively small guns in terms of the air reservoir capacity, so use the pneumo-vacuum system to augment the gun's performance. This gun has been discussed elsewhere on this forum in another thread.

 

[settingsteel]

for some reason I never liked the line tied to the front of the shaft, now I know why:blackeye

...copied the idea from Mark almost thirty years ago.

Sounds like you've been around for some time Don Paul

 

[Don Paul]

for some reason I never liked the line tied to the front of the shaft, now I know why:blackeye

Sounds like you've been around for some time Don Paul

Your only as old the girls you date.....:friday:crutch.

Cheers, Don Paul