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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.
Here are few pictures of my new versions of tomba for the Cyrano.
The gun could be any out of the box gun, without any modifications, and any adapter permanently fixed to the muzzle. Everything is made just with the hand drill and the grinder.

This is for the 6,5 mm shaft.



This is for the 7 mm shaft. My intention was to make the line slider as hydrodynamic as possible. The same setup could be used in a wet barrel mode too. The slider is 10 mm stainless steel tube. I made it to be like a plug for the bottle winding sewing thread with addition of some elastic glue. If I had a lathe I would made it differently.


The slider should be fixed to the line with the fishing knot above the annular groove.

This would make the slider most hydrodynamic. The line tied to the slider could be short piece of 1,6 mm spectra. After that comes the monofilament line.
 
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Reactions: devondave

What I am going to improve next is to make the rubber tubing and the plastic shield in front of tubing, as slim - hydrodynamic, as possible. In that case the drag would be minimal. To remind, there is no friction to the shaft in this type of tomba. As I know this is the only vacuum barrel system that has no friction to the shaft after shooting.
 
As I said in an earlier post I think it would be advantageous to make the muzzle port sealing tube flexible at one end (probably the front) so that it can lift up or flare outwards if it has to allow water out of the muzzle in case of a slow leak and loss of vacuum in the inner barrel. That way the gun will not be braked as much when compared to the ports being completely sealed with a rigid plastic cover. The problem will be to find rubber tubing of the right size. During loading the rubber sleeve section will be sucked against the muzzle ports sealing them off as the spear shaft is inserted in the gun. A plastic ring could be used to compress the rubber sleeve at the rear end, or maybe a plastic cable tie. With the right tension on the rubber sleeve against the cylindrical muzzle body you could make it so that it could be slid further back to open the ports completely for normal water filled barrel shooting or forwards for vacuum barrel operation. This is the system that should have been used on the "Airbalete", that plus an "O" ring carrying version of the "microspeed" line slide. I mentioned this on the "Airbalete" thread as a possible "tri-power" arrangement for that gun, but the suggestion seemed to pass without comment.

High power - vacuum barrel operation; medium power - flooded barrel and rubber tube valve over muzzle ports opened by sliding sleeve back; low power - flooded barrel and rubber tube valve over muzzle ports closed so that rigid section of tube is sitting directly over muzzle ports. Maybe we will see this arrangement one day. The rubber sleeve valve will be a consumable item as it will be degraded by sunlight over time, but would be very easy to replace.
 
popgun pete said:
As I said in an earlier post I think it would be advantageous to make the muzzle port sealing tube flexible at one end (probably the front)
Click to expand...

Peter, this one at the picture is of that kind - flexible, not rigid so it works as you described. It is not necessary to be flexible if the sealing and the keeping of the vacuum is perfect, but it is a useful feature.
I agree about what you suggest.
 
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Peter, that what you suggest is how I use my Cyrano right now, plus combination with 6.5 mm and 7 mm shaft.
 
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Tromic, would it be possible for you to quantify the variation in the three firing power options with your Cyrano gun by measuring the energy of the shots for each condition?

That is shooting with (1) vacuum inner barrel, (2) flooded inner barrel with fully open muzzle relief ports and (3) flooded inner barrel with closed muzzle relief ports. A variation on the last option would be closed ports with blow-off closure (soft rubber coverage) and closed ports with rigid closure (the fully sealed port condition). Air-filled inner barrel guns (as distinct from vacuum) used blow-off valve ports that kept the submerged barrel from flooding, but the gun had to be orientated muzzle downwards and water still intruded with increased ambient pressure, so these were really surface operated guns or only used at shallow depths.
 

I already did it for (1) and (2). (1) is 25 % better than (2) in shallow water. In deep water even much more. I was not interested for case (3). (3) would depend a lot on the rubber tubing properties as flexibility, thickness, etc... On my Cyrano I rather use the power switch. It is more convenient. What I am going to investigate next is the influence of different ways of binding the line to the shaft: front end like at tovarich with/without loop of line through the hole in the shaft, regular to the slider etc.
 
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There's loads of info about all sorts of dry barrel systems but I can't find much about testing line slider/line attachment.

Seems to me the easiest way by far to create a dry barrel is to have the seal in the gun muzzle and have a spear with no stop on the tail end. In this case attaching the line to the head of the spear seems again to be the obvious simple way of doing things.

I think Greekdiver Harry in Florida uses this system and he seems to make very long accurate shots as seen on his vid's.

What I'd like to see is some testing and some results/practical opinions of line attachment rather than the theory.

Anyone?

Dave.
 

Dave, this is very similar configuration to that you are talking about. The result of test was very bad. It seems that the drag of the piece of spectra attached to the head was very high. Although this was vacuum barreled gun it was outperformed with wet barrel gun by 110 %. I could not explain how it is possible. Is it possible that the 1.6 mm spectra cause such a high drag or the cause is the loop slider made from spectra at the back and of the shaft (look at the picture)? The same gun, with same, arrow but without the spectra attached to the head of the shaft was 48% better than the factory gun - wet barrel.
 
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Thanks Tromic, I figured that you would have done the first two cases, i.e. vacuum and standard wet barrel configuration, but my interest in the third wet barrel and closed ports configuration was to find out what the spread of shooting power would be. If the latter is say 15% less than the wet barrel with open port situation, which I think is the figure that Omer claim for the "Airbalete", then that gives a range of shootings powers of 40%. That is a good enough power spread to eliminate the partitioning system inside a pneumatic speargun. Hence a "Cyrano" could have its power regulator bulkhead removed and still have some useful variability in shooting power. No need to drill holes in the power regulator bulkhead, you just remove it and plug the cursor control shaft opening in the handle.

The situation with the "Airbalete" is simpler, just convert the rotating muzzle cover to a sealable rubber tube valve version and arrange a sealing system for the microspeed slider, possibly a rubber tail bush that seals on both shaft and muzzle, something like a cup seal. The pneumo-vacuum operation "Taimen" speargun uses a rubber seal permanently mounted in the muzzle to seal the shaft, but a smaller version could be mounted on the shaft and backing the slider unit in the Omer pneumatic speargun. That would do away with the muzzle "O" rings on a vacuum muzzle, but the gun would need to be supplied with spare seals as they would, like conventional sealed slider "O" rings, be consumables.
 
How did you get 40% range from 15% less power?
It would be interesting to investigate - measure Cyrano's performance as it is and with eliminated partitioning system.
Is it something similar to this UBL - UBL - underwater ballistics laboratory
Could you, Peter explain this? Is this similar to any type of tomba I already described? Could you post any picture to be more clear to me?
 
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Tromic, 25% (your figure) plus 15% (Omer's), highest to lowest. It will not be exactly 40% as both numbers refer to the "mid-power" as the base value for the percentage.

Check the thread on the "Taimen" speargun, I wrote some notes on it some time ago.
 
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The stainless steel stop ring on a Mares spear shaft is about 13.5 mm in OD. Although I call it a stop ring, it is actually a shaft centralising ring to align the shaft in the centre of the muzzle. The recess in the front of the muzzle that the stop ring locates into is slightly larger than 14 mm in diameter and a 3/8" ID x 9/16" OD "O" ring will squeeze inside the recess with an interference fit.

If one could use a rubber cup type washer (rather than an "O" ring) with a 9/16" OD and a slightly smaller than 7 mm ID then the sealing action on the shaft (7 mm in this example) and the muzzle could be accomplished with just the one seal. As the "Airbalete" uses a "microspeed" slider which also serves as a stop ring, it all being one metal piece, then a washer could sit in behind the slider and seal both muzzle and shaft simultaneously. I have only seen photos of the "Airbalete" muzzle, however the "microspeed" slider seems to be a neat fit in the front of the muzzle.

The single seal idea derives from the RPS-3 speargun which uses a captive muzzle seal to hold water in, it employs a fat rubber ring washer (a rather poorly moulded one!), not an "O" ring, to seal the shaft in the muzzle. The rubber washer in the muzzle acts like a stuffing box and creates a dynamic seal (but not always!) on the spear shaft. I know all about the RPS-3 as I have completely reduced one to its bare components, unfortunately destroying parts of the gun in the process. The manufacturer never intended some parts to be disassembled (a bad crack in the rear housing had doomed it anyway through being over tightened by some misguided individual).

The "Taimen" speargun appears to have been strongly influenced by the RPS-3 in a number of areas if you bother to inspect the design closely, even though it is a pneumo-vacuum speargun while the RPS-3 is a hydropneumatic. Both seal their muzzles on the spear shaft and have trigger mechanisms using a vertical sliding sear action.

The "Taimen" also uses a single rubber seal at the muzzle, it is a "top hat" shape in side profile and held captive in the muzzle. This gun seems to hold a vacuum in the inner barrel OK, so why not use this idea in the standard pneumatic gun, but let the rubber seal be an interference fit in the muzzle and not trapped there mechanically? When you muzzle load the gun the friction of the shaft sliding through the rubber seal will push the seal firmly into the muzzle recess. Then when you fire the gun that friction will push the rubber seal clear of the muzzle and it will ride away with the shaft, eventually being pulled back on the shaft by the shooting line to hit the stop diameter on the shaft tail. The cup part of the rubber seal shape would be to wrap the back end of the slider which will need to be reduced slightly in diameter for a short distance. This is because the outer periphery of the cup section of the rubber seal will be the centralising agent in the muzzle rather than the metal back of the slider which serves this purpose on the unmodified gun. Sealing action may be helped by introducing a small truncated conical taper where the slider connects into the rubber cup seal.

A drawback of this design may be that the repeated impacts of the shaft stop diameter may eventually chew up the inner edge of the rubber seal, so it may need a small metal washer located immediately behind it so that the rubber seal only gets sandwiched between the opposing metal faces, the other face being the rear of the metal slider.

This system would be combined with Tromic's rubber sleeved muzzle, eliminating the need to make an aluminium muzzle without relief ports.
 
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Peter, what you described is very similar to this, but with different sealing element:



The only sealing element is the O-ring at the shaft. The O-ring over the metal ring only ensures higher friction so that the metal ring is in place up to the moment when it is knocked out with the but at the shaft end. Another function of the O-ring over the metal ring is to insure better shaft centering. This is useful especially during the loading of the shaft - it prevents uneven pressure to the O ring and thus loosing vacuum. Actually the metal ring could be without the O-ring on it - it is useful but not necessary. The system works in both configurations. I had tested both of them. The slider is made in plastic to be light to minimize the impact to the metal ring and the O-ring. This slider at the picture could be made more hydrodynamic to minimize the drag. As I learned from testing and measuring the gun performance the drag is the most important factor which should be kept as low as possible. For example with this type of harpoon:http://images.google.hr/imgres?imgu...rev=/images?q=cressi+speartip&hl=hr&sa=N&um=1
which is not very hydrodynamic we lose about 15 % of energy. This shape is better:http://www.salvimar.com/images/stories/scheda_prodotti/arpioni1.jpg
You said: "The cup part of the rubber seal shape would be to wrap the back end of the slider which will need to be reduced slightly in diameter for a short distance." I think this would produce parachute effect and higher drag.
 
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The idea is for the OD of the cup washer to be very close to the outer diameter of the metal slider, it sits in behind it in a step as the rear of the slider is machined down so there is not much rubber protruding to cause a parachute effect. Plus there is the metal flat washer behind the cup washer that stops it bending backwards around its periphery. The main thing about this design is the inner and outer edges of the rubber cup seal both perform a sealing task. It could possibly be done with a fat "O" ring possessing the necessary inner and outer diameters, just to try the idea out as an "O" ring would roll off the end of the shaft. I checked an "O" ring catalogue and there is a ring with a 1/4" ID and 9/16" OD, so one can purchase "O" rings with bigger rubber cross sections. Ideally one needs a ring with the correct ID for the shaft diameter to have the right amount of interference fit inside it.
The rubber seal version acts like the drain plug in a wash basin, only it has a hole through the centre of it for the shaft where it also has to seal. It would be a very simple solution once the appropriate rubber seal was sourced. Omer already make the metal slider that would be used.
 
Most of the time I have no idea what you two are talking about , but it all sounds very clever . Having bought my first pneumatic ( Cyrano 850 ) , I read and reread all the posts on pneumatic guns and came to two conclusions :-
1 . I am an ignoramus .
2 . You two should , between you ,design the ultimate pneumatic .
With input from the likes of Foxfish and others I'm sure it could be done .
Then it could be given away to a lucky db member ( me ) .
What could possibly go wrong ? After all look what a great success the bandgun project turned out to . . . oh , um , well I'm sure this one would work OK .

The spec' needn't be too demanding , multiple firing spears , 25m killing range , laser guided sights , self loading , just simple stuff really . Nothing the brains on hand on db can't handle , I'm sure .

In anticipation ,
regards ,
Dave .
 
Peter, I understand your concept but I am afraid it would not function. The rear of the slider should be more thin to accept the cup seal. In that case it would easily break-cut the sealing element and it would not be itself enough strong to withstand the impact from the flat metal washer and the butt at the shaft end. If the mass of the slider is 8 gr and the speed of the shaft 20 m/s than there would be 1.6 J of energy in impact - too much for the sealing rubber.
 
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Thanks, Dave. I am not going to make a new gun. I just tray to understand how to use is right way: what is wrong, and what is right.
I also have Cyrano 850. I haven't been very happy with it an I was trying to find out what was wrong. Now I know how to use it right way.
Regards, Tomislav
 
Dave, we (omd & myself) have talked about this many times...
We would like to see the air chamber below the barrel (or the barrel mounted on top of the chamber) & there are a few post & design pics on the site somwhere?
The new omer is a little step falward but the basis design is still very - well basic!
 
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