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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.

Answer is yes to all your questions!
 
Seriously, do people in general lift their guns out of the water before inserting the spear...? What a hassle... For that reason alone, your newer Tombas with a valve could be a big improvement.

All best,
David
 
Diving Gecko said:
Seriously, do people in general lift their guns out of the water before inserting the spear...? What a hassle... For that reason alone, your newer Tombas with a valve could be a big improvement.

All best,
David
Click to expand...
https://www.youtube.com/watch?v=ts1Z70E4UkI&feature=plcp

[ame="http://youtu.be/PIptyCt8wMw?t=58s"]PIptyCt8wMw?t=59s[/ame]

Seriously, you need to drain water, it lasts 3 seconds, after that you load gun under water.
 
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I will, I guess I have to. I am just looking for simplicity;-)
But if your dad found a solution to this - then Tomba would have something none of the other kits have. Perhaps another selling point even to all those guys who already think an airgun is too complicated and takes long to load.
If there was indeed a little release valve in the barrel between the o-ring and the piston (in its most forward position) then when the spear was pushed in, the water would escape. Or it would escape on firing. Either way, it would mean not having to worry about lifting the barrel out of the water before inserting the spear.

But the way, what happens if I don't lift it out to empty the water? A tiny performance impact or can water sneak behind the piston?

Also, now I am wondering about something that might be worth a new thread, but what is your opinion on a replacement piston? Is it worth it? Both LGSub, STC and I guess you(?) make them. I also read, that a lot of the Italian air spearos polish the inside of the piston barrel. Any thoughts?
 
trromic said:
I think I will make this one for 7 mm "free shaft" for Mirage 70.

Click to expand...

Hi Tomi,
Looks nice and simple. Would it be worth it to open up the front of the sliding damper a bit to aid in loading? Or would the slider lose too much "braking power" with less frontal area? The drawing doesn't show but will the o-ring still slide to a bigger recessed area after firing to make it compress less?

Here is your drawing where I tried to make the damper opening help in centering the spear - if it would be feasible.
 

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  • DH_free7hydrodamper.jpg
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You can make that modification, but I don't see it is necessary. Shaft and is cone shaped. I would rather add add polyurethane disk on opposite side, toward the piston.
 
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While damper is braking on 10 mm distance, spear runs 20 mm. That's because the average speed of damper is 2 x smaller than the speed of spear. This is very important to have on mind for good design of hydro damper.
 
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Still another idea. All-in-one Tomba for 7 mm "free shaft" with hydro damper, all with only one O-ring 15 x 7 x 4 mm. However, piston must have bushing inserted to accept the shaft so hydro-damper could work properly. That makes it about 5 g heavier (titanium). While not using the gun, O-ring would be under constant pressure of about 30 kg so might require changing regularly. Muzzle tip screw has delrin or teflon bushing to center the shaft during loading. There are also 5 x 2,5 mm holes to let water in and out for hydro-damper. It is probably possible to make it even more simple! This is the first sketch.



From such a rifle is not necessary to empty the water before putting the spear. Absorber would have to be very quiet and efficient.
 
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These are design requirement to fulfil so hydro damper might work as required.
To ensure emptying water in front of piston, during shaft inserting, shaft should be made thinner (a).

 
I really like this latest design. I wonder if the best modification to the shaft would be to make the diameter a bit smaller at the end on a lathe or cut one or two small channels in the shaft - perhaps it can be done with a small angle grinder or a powerful Dremel tool?
You did make one hydrodamper muzzle already, right? How do you feel about the concept in practical use?
 

In latest design, you can see, piston should be modified to have deeper boring to achieve "2d" length. But that way both piston, and damper body would become lighter.

I would say I prefer hydro-damper. Just should find out the best design, to be reliable and easy to use with max comfort and minimal/no modifications to standard parts like piston and shaft. Obviously muzzle must be modified.
 
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True, I agree that the goal must be to have to modify stock parts as little as possible. But what I really like with the latest design is that you no longer have to lift the gun out of the water. Without having tried it, I don't think it is that easy to hold a long gun vertically in one hand while inserting the spear with the other. What if there is big waves and such. I really think if you can make a version that drains the water itself, then you are another step ahead of the alternatives out there. If it is true that water in front of the piston is a real no-go, then I would really like a self-draining design.
 

With regular shock absorber, especialy using vacuum bearrel "free shaft" if you do not let the water out of the muzzle and prior to shooting you aim little down, shock absorber will be flooded and could not work!
 


 
Back to real hydro damper, for 7 mm shaft. I already made hydro damper for 8 mm shaft with slider. This might be my next project.

This is very simple. But requires changing of original (stock) shaft. Shaft should be flattened on one side so water can get in and out of the gun using that free space.



This version could use original, unchanged stock shaft, but is more complicated to make and use. Usage is similar to Evo-Air. Gun must be loaded under water. When loading the shaft, additional water (for hydro damper) is pushed into the gun (about 1,3 ml). On shooting that water is used for hydro damper work. On shooting, under water pressure, O-ring is moved forward opening water exit holes.

 
trromic said:
Nicer:

Click to expand...

Ah, actually, I just realized something pretty banal... Even if the muzzle head needs to be screwed in and out prior to shooting (like an Evo-Air), then that is likely still better/easier than having to empty the barrel lifting the whole gun out of the water, wouldn't you say? I know you guys say this is easy enough. Just wondering how it would be to balance a 115-130cm gun in one hand while inserting the spear. This surely must be easier.
 
Yes, you are right! That is better solution than emptying water from barrel before each loading. And, you'll get more efficient shock absorber in same time. Water in barrel is now welcomed! Also lubrication of piston seals and the O-ring in muzzle would become better. Actually there is no screwing, just sliding forth and back and locking. Locking is required to ensure some additional water would be injected in a barrel, about 1,5 ml. Without locking, the O-ring would be pushed in front position and water for hydro damper would not be injected.

Another solution, withought sliding-locking, would require modifiing every shaft used with the gun.
 
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