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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.
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tromic

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Aug 13, 2007
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Water must be drained from the Tomba muzzle before loading the shaft. Otherwise the O-ring could not be pushed into the muzzle.
There are a few way how this inconvenience might be solved. For usual on breath diving while preparing for next dive one can insert the shaft under water and then just for a moment rise the gun above water almost level but tip toward the water surface so the water can be drained from the muzzle. Then push in the o-ring and the line slide. That is how I do it. This way is not possible for scuba divers.
Without changing the existing design one way might be accomplished using slightly different way of inerting the shaft with the O-ring and the line slide.
Only tiny intervention is required on the shaft. That could be accomplished using small diamond powder coated file. A small shallow indent should be made below one part of the O-ring as on the image so the O-ring won't seal well in that position. It could be only 2 mm long and 0.5 mm deep.

1573910149668.png

After the shaft, cone ring, O-ring and the slider were inserted (fig a.) additional push to the shaft itself (fig b.) have to be done for 1-2 mm so that the indent will pas the O-ring and 100% sealing is obtained.
 

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popgun pete

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Jul 30, 2008
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As has been mentioned before you could add a ring valve with just one hole for the hydraulic lock to be automatically released, either an "O" ring or just a rubber band with a rectangular cross section to fit a matching groove cut into the muzzle.
relief valve.jpg

That is the solution used for the LG-Sub muzzle, although it ejects water through the nose of the short muzzle. That reminds me that I was going to buy one of those “Black Head” muzzles, but forgot about it.
 

Zahar

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Jun 3, 2014
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The hole must be made in front of the piston and not behind the piston! The piston abuts against the shock-absorbing sleeve and, under air pressure in the receiver, blocks the access to water by the shock-absorbing rubber hose on the sleeve!
 

popgun pete

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Unless the piston has a hole in it as well, as once they did have. It is not difficult to drill a small hole in the side of the piston.
Mirage CRX.jpg
Mares metal piston 3 seal type.jpg
 
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tromic

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I already have the O-ring solution ready in my design schematics but did not applied it yet. Actually it is not very important to me. Other thing is because Marko made everything as light as possible so there is no place for the grove for O-ring. I do not see any problem if I just have to push the O-ring and the slider into the muzzle above water surface. It takes only few seconds. And it is better not to have any water left in the muzzle especially for Tomba700X model. This is because Tomba700X has tiltable delrin insert in muzzle (that makes loading more fluent if the shaft is bowing) and water left behind it in muzzle might damage it.

1573997415413.png
 
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Diving Gecko

shooter & shooter
Jun 24, 2008
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I already have the O-ring solution ready in my design schematics but did not applied it yet. Actually it is not very important to me. Other think is because Marko made everything as light as possible so there is no place for the grove for O-ring. I do not see any problem if i just have to push the O-ring and the slider into the muzzle above water surface. It takes only few seconds. And it is better not to have any water left in the muzzle especially for Tomba700X model. This is because Tomba700X has tiltable delrin insert in muzzle (that makes loading more fluent if the shaft is bowing) and water left behind it in muzzle might damage it.

I think it could become a slightly bigger hassle the longer the gun is. I personally don't feel like yielding a 140cm long gun out of the water. Also, when I boat dive, raising a gun out of the water is our sign to be picked up;).
For shorter guns, sure it should be easy enough.
 

tromic

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Aug 13, 2007
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Well, you are right Davide, there might be situations when it is not convenient.. My son Marko also had been loading his Asso130 this way. But anybody can nowadays choose between large number of different guns and kits.. :)
 
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popgun pete

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The plastic ring replaced the conical front rubber barrel bore wiper seal, early versions of the "Mirage" used the three rubber seal piston shown in the photo. The grey plastic ring had a crack splitting it on one side so that it could be fitted over the piston nose and then sit snugly in the recess provided for it on the metal piston body. The idea was to stop the piston wobbling in the inner barrel as the plastic ring provided a bearing surface. Piston sliding friction was reduced compared to the three seal piston, but if sand got trapped in the plastic ring it could scratch the inner barrel.
 

tromic

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Aug 13, 2007
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The plastic ring replaced the conical front rubber barrel bore wiper seal, early versions of the "Mirage" used the three rubber seal piston shown in the photo. The grey plastic ring had a crack splitting it on one side so that it could be fitted over the piston nose and then sit snugly in the recess provided for it on the metal piston body. The idea was to stop the piston wobbling in the inner barrel as the plastic ring provided a bearing surface. Piston sliding friction was reduced compared to the three seal piston, but if sand got trapped in the plastic ring it could scratch the inner barrel.
Thanks. I have the same piston, so nothing is missing.
 

tromic

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Aug 13, 2007
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This how I calculate the hydro-damper slider or piston:

1574424582611.png


S0, S1, S2 - surface exposed to water in m2;
mk, Vk - mass and speed of the slider relative to the shaft;
mv, Vv - mass and speed of the water expelled by the shaft tail end;
Ek, Ev - kinetic energy of the slider and the water - should be Ev equal or higher than Ek.

I've already tested this calculation on several titanium and stainless steel sliders and on two pistons, one of them was my Mirage hydro-damping piston/shock absorber and the other of my russian friend Сергей (ECK). It seems to be acceptable for real life calculation.
 
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tromic

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Aug 13, 2007
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This is a reply about Tomba800 about loading under water. Even I was surprised, but it is possible and it is very easy.
If you hold the slider pushing the O-ring against the muzzle, while loading the shaft, only for few mm, the vacuum would be preserved.
After that few mm when the O-ring enters the muzzle you can proceed the loading as usual.
 

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Diving Gecko

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Jun 24, 2008
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This is a reply about Tomba800 about loading under water. Even I was surprised, but it is possible and it is very easy.
If you hold the slider pushing the O-ring against the muzzle, while loading the shaft, only for few mm, the vacuum would be preserved.
After that few mm when the O-ring enters the muzzle you can proceed the loading as usual.

That’s great news Tomi. And congrats on that feature, even if unintended:)

You know, I have long been an advocate for being able to do this, especially on long guns or if the sea state is rough.

So, now, this slight limitation of the Tomba is no longer:)


Sent from my iPhone using Tapatalk
 

tromic

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Aug 13, 2007
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Yes, Davide you are right. I did all improvement to Tomba design thanks to interaction with happy or unhappy users. I had not much opportunity to test Tomba in water because I am few hundreds km from the sea and I could test it myself only once a year during vacation. All the feedbacks from the users were very helpful for me, and I appreciated them a lot. This Tomba800 was an earlier design or it was maybe Tomba800X, I am not sure, but the same method of loading under water is applicable in both designs. The main advantage of Tomba800X over elder Tomba800 is easier loading if the shaft would bowing during loading. This last case revels another new possibilities without any change to the basic Tomba design but different method of loading, I always prefer designs as simple as possible because they are also more reliable. It seems that the O-rings life time on the shaft is also much longer than any would had been imagine.
 
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