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Tomba - All in One barrel sealing

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.

Yes, Diving Gecko. You are right! Cone shaped groove for the O-ring might be a part of the solution... together with lower OD of the tail stop diameter, maybe 7.5 instead of 8 mm, and PU ring inserted. I had a plan to test it...but I had not. I believe it would work but it would require modification of the shaft, and that is not very convenient. Using the same shaft would be beneficial for the Vuoto or STC too.
 
Tomi,
Just wondering - what's the benefit of the PU ring?
Is it as a sort of shock absorber/wedge for the slider since the spear tail is not very large and as such have very little area to hold the slider?
 
tromic said:
You might try using PU, but there could be some other kind of problems too... I am not sure how would it perform on higher pressure, especially when the spear gun is unloaded and the piston rest on PU? I suppose PU damper would become deformed?
Click to expand...

I've been looking around a bit more and STC, Evo-Air (Gen 2), LG-sub and Pelengas all use PU absorbers.
STC and Pelengas use two different hardnesses with the hardest one nearest the piston. LG and Evo-Air has only one.
My Evo-Air absorber has cracked a little but otherwise shown very little deformation. The PU in my STC absorber has no deformation but the internal Delrin skeleton is not only cracked but also bulging inwards.
The STC is the only one of the four having this internal skeleton supporting the PU as far as I can tell.

This was just to share some info. I still have no idea which approach is best.
 
Thanks for the info! I suppose that only long testing under real conditions, can give the best answer - which is the best.
 
tromic said:
Thanks for the info! I suppose that only long testing under real conditions, can give the best answer - which is the best.
Click to expand...


No worries, it's always good to share our thoughts.
I noticed Pelengas is also using the PU ring at the spear tail - can you tell me your thoughts behind the PU ring? I guess it is a safety and shock absorber when using a tail end with a very small step (small OD, not much difference to OD of the spear)?
 

Yes, you are right. It is common to use PU damper on the shaft in Ukraine, Russia...
It has cone shape toward the slider opening.

 
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The slider can jam on the polyurethane tail bush, but it is easy to pull it off by using the shooting line wrapped back against the shaft and giving the line a sharp jerk, of course you need both hands on the shaft to do it. The polyurethane tail bush minimizes the effect on the muzzle vacuum seal's lip as the larger diameter of the spear tail stop diameter passes through it, there being no sharp edges as there can be with a metal step at the change of diameter even if the leading edge is tapered.
 
Yeah, definitely should have less wear on the seal. And if there is less wear and mushrooming of the tail end, that's good, too. But if it tends to get stuck after each time, then that would be annoying. Imagine being in a school of fish and wanting to reload quickly and having to go through that extra step.

Obviously, less wear is good, but how long does the PU last for?
I saw Tomi's video of how to put the PU ring on the shaft and while it is doable, it is not a quick change you do on the boat at sea.

So, as much as I really like the idea of making seals last longer and downsizing sliders for better hydrodynamics, it would be good to have an idea about the reliability of this type of setup? I mean, it looks simple, but in real world use, is it still simple and durable?
Tomi, what does the Russian's speaking forums say about this?


Finally, I see that the tail end has no taper as on our regular shafts where the tail is held in the piston by friction. With the "Cyrillic" tails, what holds the spear? The vacuum in the barrel? What if you hold the gun vertically, isn't there any risk of the spear slipping a few cm? That could be a problem once you fire.
If not, then I like the idea as there will be even less force on the shock absorber on impact.
 
On a "Taimen" speargun the inner barrel vacuum holds the spear in the inner barrel, so no taper needed on the extreme rear spear tail spigot to jam the shaft tail in the piston face, it just sits there instead in a cylindrical recess with a metal rear wall that will push on the shaft tail during the shot. The "Pelengas" has a tapered spear tail, so there the spear tail does jam into the piston face, although that gun has so many variations being made to it that situation could always change in the future. "Taimen" developed the polyurethane tail stop as otherwise the metal shaft tail stop was going to tear up the vacuum seal if the trapped water inside the inner barrel failed to push the seal open just in advance of the tail stop arriving at the sealing lip.

The polyurethane tails do wear out, but how long it takes depends on the conditions and frequency of use and keeping the surfaces free of grit after and if the spear has been dragged along the bottom. I twist the tail around between the fingers of my diving gloves after a shot, but it also depends if I have time or remember to do it.

As a side note this website is generating security warnings in my virus alert software, something about certificate error or being out of date wrt validity!!!
 
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Cool vid.
I've been talking to Dima (UBL) but a 12mm on my Mirage would make the gun too heavy, I think. And increase the pressure too much for the 10mm loading barrel to work well.
But Dima, Calibro 12, LG and now, Omer keep mentioning how the 12mm is the most efficient size for a barrel. What is it that they base that on?
 
Here is another video from guy which name is Fabio (from Italy), David I do not know answer of your question.
On previous video is also Fabio.

 
The answer probably depends on the definition of efficiency for the purpose and that will depend on the weight of spear being thrown to defeat the target. No point having high efficiency if the spear bounces off that target. Some testing in Russia has shown that 10 mm is the most efficient, but other factors can affect the results and I doubt someone made a bunch of guns with only a variation in the range of barrel bore sizes being used.
 
There is a widespread perception that the 13 mm barrel is better in dry (vacuum) barrel usage than 11 mm, if using 6.5 to 7.15 mm shaft.
But with water barrel certainly is better 11 mm (or 10 mm) than 13 mm. 12 mm is a compromise. Also 12 mm requires less air pressure than 11 mm for the same shooting performance so is more convenient.
On both videos above spearguns use Tomba700X.
 
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Reactions: Diving Gecko
Some users of Tomba noticed that Tomba is more silent comparing to other dry barrel kits using line slider.
This might be an explanation...

 
Reactions: Diving Gecko
I paid subscription for imageshark for one month, so the images are now visible.
 
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tromic said:


Click to expand...

I managed to make stainless steel slider using silver brazing. This was my first attempt ever using this method.
The body of the slider was cut from a piece of tubing (10 mm OD) and shaped using grinder.

 
Reactions: foxfish
Looks good Tomi.
I have some titanium sliders come in in a month or two. Will weigh them and report back.
They are meant to work without a slide ring and even without a rubber bumper. Will be interesting to test them.
 
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