Tomba - All in One barrel sealing

[tromic]

Cone


Cone, O-ring, Slider


Knot Slider


Slider


Train

 

[popgun pete]

Tomislav, I do not think that you have to worry about the weight of those small parts. The tail cone ring is part of the restrained mass which includes the spear. A centimetre longer spear will have more mass than any changes to the stop ring or tail cone ring. In fact the longer the spear shaft then the more of a squeeze will be applied to the single sealing "O" ring. If Don Paul's longer gun does not crush his Tomba "O" ring in the short term then the system will be fine as is. Don Paul can always add that rubber pre-washer to the Tomba that you sent him. Think of an "O" ring sitting on an anvil (the rear face of the line slide) being hit by a hammer (all the metal sliding parts, the majority of the mass is in the spear). Then put a thin sheet of rubber over the "O" ring and repeat the exercise. The "O" ring will last longer as the rubber sheet absorbs and spreads the impact and reduces any nipping of the "O" ring.

 

[Don Paul]

Ill try to get some more water time this weekend off the beach, I really miss my pool. I have been inspecting the O- ring and slide ring with a lupe and all is well. Alpha grade Ti and a UHMW or G-10 washer or multiple O-ring could be employed if needed after tests at 20 bar.

Cheers, Don

 

[popgun pete]

The mass, or weight, of the line slide may affect the Tomba "O" ring as the latter has to accelerate the line slide up to the speed of the shaft when the shaft tail exits the muzzle. At that moment the spear shaft has reached maximum velocity just as its tail stop diameter collides with the stop ring, or tail cone ring, which may be sitting motionless in the muzzle, and drives it up from zero to maximum spear velocity in an instant. The same acceleration is applied to everything in front of the stop ring. The impact and sudden acceleration will not affect the metal tail cone ring, but pushing the line slide up to velocity will compress the cross-section of the "O" ring located in the space between them. Hence "O" ring damage may not occur solely at the end of shaft flight, but at the beginning as well when using a metal line slide. A plastic line slide would be easier on the "O" ring (less inertia), or you could add something to dampen the impact. Possibly you could use the "Cyrano" line slide with your Tomba, it is reasonably streamlined (once you cut the plastic mould flash off some of them).

 

[tromic]

Tomislav, I do not think that you have to worry about the weight of those small parts. The tail cone ring is part of the restrained mass which includes the spear. A centimetre longer spear will have more mass than any changes to the stop ring or tail cone ring. In fact the longer the spear shaft then the more of a squeeze will be applied to the single sealing "O" ring. If Don Paul's longer gun does not crush his Tomba "O" ring in the short term then the system will be fine as is. Don Paul can always add that rubber pre-washer to the Tomba that you sent him. Think of an "O" ring sitting on an anvil (the rear face of the line slide) being hit by a hammer (all the metal sliding parts, the majority of the mass is in the spear). Then put a thin sheet of rubber over the "O" ring and repeat the exercise. The "O" ring will last longer as the rubber sheet absorbs and spreads the impact and reduces any nipping of the "O" ring.

Peter, look at the last picture - "Train". I put two O-rings and a washer between them. Only the back O-ring is for sealing. The other, front, just get 1/2 of energy to O-rings. In this last "light" configuration, with plastic slider, it is not necessary. I did some calculation and measurement. One O-ring can get about 1 J of energy to be safe of damage. So if we have 3 g in front of the O-ring (slider) that acts like a hammer, at 25 m/s it is about 1 J. If more than 3 g it might be dangerous to the O-ring life. In current configuration there is 1.7 g in front of the O-ring so O-ring will be safe, I suppose. I know in water it would be different, more dangerous for the O-ring, but is impossible to calculate. I hope would be OK. I also don't know the real starting velocity of the shaft in the water. I suppose it might be less than 25 m/s, maybe about 20 m/s.
This last shaft kit (Tomba12H) will be soon tested on 32 bar or even more (Spark, 7 mm shaft).

 

[popgun pete]

It will be interesting to see how the "Train" idea works with the metal slider (line slide). Another possibility which you could try is a cone machined on the rear end of the metal slider. The idea is that it will stretch the single "O" ring radially outwards and the inner tip of the cone will then touch the flat front face of the tail cone ring behind the "O" ring. This bypasses the "O" ring from the "big squeeze", but success will very much depend on the tip of the cone on the rear of the metal slider not damaging the inner periphery of the "O" ring as the conical face spreads it. "O" rings can take a small amount of stretch without permanently distorting them.

 

[popgun pete]

One way to look at this problem is to consider what a stop ring does besides centralizing the shaft in the muzzle on some spearguns. Usually the step at the shaft tail is 0.5 mm, e.g. an 8 mm diameter shaft has a 9 mm shaft tail stop diameter, a 7 mm diameter shaft has an 8 mm shaft tail stop diameter. That 0.5 millimetre step would pull through a plastic line slide, wedge inside it or split it, hence the addition of the metal stop ring increases the diameter of the step for the rear of the line slide to impact against. On spearguns with metal tube line slides (with loop style "ears") the line slide is also the stop ring if the gun does not require a centralizing washer at the muzzle, this is the situation with some hydropneumatic spearguns.

As ultimately all the pull force of a fighting fish is being resisted by that 0.5 mm step on the shaft and is being transferred through the line slide body to the shooting line, then we can use a similar size step elsewhere in the line slide. If the rear face of a machined metal line slide has a small central cone with a rear lip step of 0.5 mm that lip can act on the tail cone ring or stop ring's front face to resist the pull of a fish, it will be a similar situation to the step on the shaft tail. With the right taper angle on the small cone and a rounded outer edge to the lip, that small cone should be able to push under the inner edge of the sealing "O" ring and displace the body of the "O" ring radially outwards. Once the tension on the shooting line ceases the "O" ring will shrink back to sit on the shaft and should be able to resume its sealing duties for the next shot.

If this can be made to work repeatedly then the single "O" ring vacuum barrel system for spearguns equipped with line slides will eliminate all other designs as being too bulky.

 

[tromic]

It will be interesting to see how the "Train" idea works with the metal slider (line slide). Another possibility which you could try is a cone machined on the rear end of the metal slider. The idea is that it will stretch the single "O" ring radially outwards and the inner tip of the cone will then touch the flat front face of the tail cone ring behind the "O" ring. This bypasses the "O" ring from the "big squeeze", but success will very much depend on the tip of the cone on the rear of the metal slider not damaging the inner periphery of the "O" ring as the conical face spreads it. "O" rings can take a small amount of stretch without permanently distorting them.

I was also thinking about that concept of stretching the single "O" ring radially outwards, but there would be some other problems. Possible damaging the inner O-ring surface and it would be difficult or impossible to push the O-ring in to the adapter with such a line slide shape.

Maybe something like this might work:

After shooting ______________________Before shooting

Line slider (plastic) should be right, next to the steel ring. Any kind plastic slider could be used, or "knot slider".

I am sure with that last very light cone ring everything will be OK, at least to 27-28 bars (11 mm barrel, 7 mm shaft).

 

[popgun pete]

What I was thinking about was very like your diagram, but the other way around, the cone shape was on the rear of the slider and your tail cone ring was unchanged. The height of the truncated small cone was the same as the width of the "O" ring cross-section, so the "O" ring could sit in the gap created by the cone without being squeezed. That way there would be metal to metal contact right through the line slide when everything was compressed by shooting line tension. Cone shapes are used to stretch "O" rings for fitting into grooves on components, so travelling up the taper of a cone should not damage the "O" ring. These cone ended cylinders or bullet shaped tools are used to replace "O" rings and are supplied in the Mares service kits.

 

[tromic]

What I was thinking about was very like your diagram, but the other way around, the cone shape was on the rear of the slider and your tail cone ring was unchanged. The height of the truncated small cone was the same as the width of the "O" ring cross-section, so the "O" ring could sit in the gap created by the cone without being squeezed. That way there would be metal to metal contact right through the line slide when everything was compressed by shooting line tension. Cone shapes are used to stretch "O" rings for fitting into grooves on components, so travelling up the taper of a cone should not damage the "O" ring. These cone ended cylinders or bullet shaped tools are used to replace "O" rings and are supplied in the Mares service kits.

If cone shape were on the rear of the slider, the slider could not be used to push the O-ring into the adapter. That would be the only problem, otherwise would be good.

 

[popgun pete]

How much of a push does the "O" ring need to set it in place in the muzzle adaptor, especially as you have a 4 degree taper at the muzzle recess entrance to let the "O" ring slide into position?

 

[tromic]

How much of a push does the "O" ring need to set it in place in the muzzle adaptor, especially as you have a 4 degree taper at the muzzle recess entrance to let the "O" ring slide into position?

Yes, with cone slider tail the adapter should be different too, to ease inserting the O-ring. That would work. :fridayI haven't been making 4 degree taper in adapter entrance in recent time. Taper is only to make a slot for the cone ring.

This is according to your propose, right?



There are still a lot of other possibilities.

 

[tromic]

This is a first aid solution when having heavy line slider and want to use it on high pressure (high speed shaft).



Let's say we have 5 g stainless steel slider and there will be 25 m/s speed of the shaft.

That would be as if the line slider with speed of 25 m/s crashes in something hard. The energy will be
E = 1/2 * m * v^2, E = 1,5 J. Under water probably more, let say 2 J.

To have that energy of 2 J we might stretch a thinner mono (0,3 - 0,4 mm) tied to the front of the shaft, with force (F) for length (s). Because energy is also E = Fa * s (Fa - average force), we should find such a solution for which

E = 1/2 * F * s , F - max force

For example:
2 J = 1/2 * 8 kg * 9,81 * 0,05 m.

So max force to stretch the thinner mono might be F = 8 kg, and s = 0,05 m. Some other combination is also possible, like F = 4 kg and s = 0,1 m.

To make all more hydrodynamic, the back of the slider could be made cone shape.

Free shaft could be also made better in performance using thinner mono for the shaft length, and after normal mono. If same thick mono (2 mm) would be used from the shaft tip, performance of the free shaft might be worse than Tomba with slider.

 

[martinbar74]

hello friends
why not to use only 2 protecting o-rings (in red) and one sealing(in black)?

 

[tromic]

hello friends
why not to use only 2 protecting o-rings (in red) and one sealing(in black)?

Would not work. It is unstable configuration. Some of O-rings would be lost in water.

 

[popgun pete]

Yes, with cone slider tail the adapter should be different too, to ease inserting the O-ring. That would work. :fridayI haven't been making 4 degree taper in adapter entrance in recent time. Taper is only to make a slot for the cone ring.

This is according to your propose, right?



There are still a lot of other possibilities.

I was thinking of a 0.5 mm vertical step at the shaft diameter contact, then a taper to form the cone where you have the horizontal flat section, so the "O" ring could not stay in the shifted position. Once the squeezing action was off then the "O" ring would slip back to sit on the shaft again. The top of the 0.5 mm step would be rounded off to have no sharp edge. Hence the cone on the rear of the metal slider would be flat topped, like a little volcano. The front face of the tail cone ring would be flat with no inner taper recess as it would just abut the flat face of the top of the cone on the rear of the slider when the parts were squeezed together. That flat top on the cone would push the "O" ring for seating in the muzzle adaptor, but once it had enough pressure on it the "O" ring would stretch and move up the cone, such as when a big fish was pulling on the shooting line. This "O" ring stretching action can be checked by pulling an "O" ring over the tail end of a spear shaft, it has the same 0.5 mm step at the tail stop diameter.

 

[tromic]

I was thinking of a 0.5 mm vertical step at the shaft diameter contact, then a taper to form the cone where you have the horizontal flat section, so the "O" ring could not stay in the shifted position. Once the squeezing action was off then the "O" ring would slip back to sit on the shaft again. The top of the 0.5 mm step would be rounded off to have no sharp edge. Hence the cone on the rear of the metal slider would be flat topped, like a little volcano. The front face of the tail cone ring would be flat with no inner taper recess as it would just abut the flat face of the top of the cone on the rear of the slider when the parts were squeezed together. That flat top on the cone would push the "O" ring for seating in the muzzle adaptor, but once it had enough pressure on it the "O" ring would stretch and move up the cone, such as when a big fish was pulling on the shooting line. This "O" ring stretching action can be checked by pulling an "O" ring over the tail end of a spear shaft, it has the same 0.5 mm step at the tail stop diameter.

One problem that might happen could be wiping of the O-ring by water, when stretched on the rear cone of the slider. It is the moment when the shaft speed is max. That is why I did not make cone shape, but horizontal.
Would be interesting to try. I would also prefer cone shape.

 

[tromic]

Another possibility:



After shooting sealing O-ring is protected by stainless steel tubing. Four O-rings acts like shock absorber, so each O-ring accepts only 1/5 of total impact energy. Max OD on the shaft is 12 mm, same as line slider. In this configuration some grease could be applied too, to make friction lower. All O-ring are 11 x 7 x 2 mm, for 7 mm shaft.

 

[popgun pete]

Another possibility:



After shooting sealing O-ring is protected by stainless steel tubing. Four O-rings acts like shock absorber, so each O-ring accepts only 1/5 of total impact energy. Max OD on the shaft is 12 mm, same as line slider. In this configuration some grease could be applied too, to make friction lower. All O-ring are 11 x 7 x 2 mm, for 7 mm shaft.

The problem with leaving the sealing "O" ring always sitting on the spear shaft surface is that it will be exposed to crushing if a large pull tension exists on the shooting line. With smaller sized fish that will not happen, your tail cone ring with tapered muzzle entrance "Tomba" system already works fine just as it is. The multi-"O" rings enclosed in a sliding outer case will work OK as a shock absorber, but they cannot protect the sealing "O" ring if a large tension exists as all sliding elements on the shaft will be subjected to the same compressive load. The idea of the cone on the rear end of the metal slider was to make minimal changes to your original "Tomba" configuration, you only need to swap the slider for use with larger fish. If it can be made to work repeatedly then the cone modification trades (or swaps) "O" ring crushing for "O" ring stretching. Being heavily crushed will change the "O" ring cross-section to an elliptical form which will render it useless for sealing if it takes a permanent set, but stretching it radially should preserve it provided the cone on the rear of the slider retains a smooth surface finish. Stretching the "O" ring allows it to sit in the gap created by the height of the cone without being crushed when the fight to subdue a big fish is on. The cone needs a flat top with a curved outer shoulder as if it has a thin, sharp inner lip then it will work like an apple corer and chop out the inner periphery of the sealing "O" ring. The metal cone on the rear of the slider has to be strong enough to resist flattening by repeated impacts with the tail cone ring; being a cone makes it stronger. Experimentation will be required to find the best angle or side profile for the cone, as you say if it is too fat at the base (of the cone) then it may stretch the "O" ring to the point where the "O" ring can escape over the forward edge of the tail cone ring.

 

[tromic]

Peter, I applied a force of 50 kg to single O-ring sandwiched in regular Tomba12, using my Easy loader. There was no damage to the O-ring. I suppose it would be safe at least to 60 -70 kg. With the "train" version that force might be few times more not to damage the O-ring.

I will probably make a rear cone type slider to try it with regular Tomba. This last drawing is just a possibility. The drawback of it is that it might be about 5 g, including slider - to heavy. The back face of the cone ring would be under sliding hammer of 7 g. Too much for high speed shaft.