Pneumatic speargun without piston

[popgun pete]

There has been some developmental work on an "inner-barrel-less" and hence "pistonless" speargun with a rear latch on the spear tail. The "Taimen" company had a video of one, but I never got around to watching it. I went searching again recently, but I now cannot find anything about it.

My assumption is a sear tooth holds the spear tail cap (substituting for the usual piston) and the gun not discharging then depends on high pressure air not being able to access the rear face of the actual spear. So there must be an "O" ring inside there to keep high pressure air from penetrating into the tail cap's interior. This would appear to be a dangerous system for a speargun. My guess is that if you use an annular rubber ring valve then you can eliminate hydraulic lock in the tail cap by pushing any trapped water out into the air reservoir as you muzzle load the spear. Then when you pull the trigger the spear tail cap releases and it and the spear both head for the muzzle. Any leaks in the spear tail cap's sealing and the gun shoots, if the rubber ring valve fails then the gun depressurizes. I don't know any of the actual details, but here is a guess in a quick sketch.

 

[tromic]

Pete, I suppose this might not work very well, but the idea is interesting.
"Piston" would be heavy, need more efficient shock absorber, collecting more water inside air barrel, less length working course of "piston"...

 

[popgun pete]

Well the central portion of the spear tail cap with the rubber ring valve could be shorter than I have drawn it and I expect that the tail cap will be made from titanium as is the piston in the current guns. Freshwater use would be more suitable than saltwater use as otherwise the gun would need to be cleaned more frequently inside to get rid of the salt.

 

[popgun pete]

Here is more compact version with damper. "O" ring placement will need to be more carefully designed, here it is only indicative. Any gap exposed to pressure where the join is will tend to blow the spear out of the tail cap, so the gap in terms of area facing the rear of the spear will need to be very small (and may not be possible!).

In order to see just how much of a "vertical gap" at the join between spear shaft and tail cap could be "safely" exposed to gun chamber pressure with the gun cocked to shoot I made the following calculation. If the gun has a 9 mm diameter spear shaft and is pressurized to 50 bar (gauge) then the annular area or shoulder step on the shaft tail exposed to this pressure must be restricted to producing at most a force which is equivalent to the force acting on the inner cross-sectional area of the spear facing ambient pressure which is zero (gauge) or 1 bar in terms of the absolute pressure for there to be no continuing opening movement between them. Here I am assuming that pressure inside the tail cap interior is zero as once the cap join opens up slightly the hydrostatic pressure drops to zero as the rubber ring valve will not transmit chamber pressure into the interior of the cap (this probably will not be true, but I just want to see what happens with only 1.0 bar (1.0 - 0) applied to this central area of the spear). The chamber pressure is 51 bar in terms of the absolute pressure. Assuming that the spear shaft's inner cross-sectional area facing ambient pressure is of radius "r" then we will have an outer annular area or step of radial height (4.5 - r) facing the chamber pressure inside the gun at the join between the tail cap and spear. As this annular area or step also faces the external pressure then the effective pressure acting outwards on it is 50 bar (51 bar - 1.0 bar).

Therefore the force F1 acting inwards will be given by pi x r^2 x 1.0 and the force F2 acting outwards will be given by [pi x 4.5^2 - pi x r^2] x 50. For the forces to balance F1 must equal F2. The value of pi cancels out on each side so that r^2 = [4.5^2 - r^2] x 50. Algebraic manipulation gives us r^2 = [20.25 x 50]/51 and therefore r = 4.4557 mm. So the annular rim exposed to chamber pressure can only be 0.0443 mm in radial thickness which is very, very small. Any more of a step on the shaft being exposed to chamber pressure and the gun shoots without pulling the trigger.

 

[popgun pete]

Maybe a way to seal the tail cap join with part of the damper unit, but reliability does not appear very convincing once the polyurethane bush wears with respect to its inner bore. Simplicity of design starts to disappear.

 

[tromic]

O-ring instead of rubber ring ...



or



Uploaded with ImageShack.us

 

[tromic]

Thanks Владимир, I've seen that:
http://garpun.spb.ru/forum/viewtopic.php?p=55365#55365

I would rather make it this way:



or

 

[popgun pete]

I see that the thread http://garpun.spb.ru/forum/viewtopic.php?p=55363#55363 now extends to 157 pages! At the beginning there was a schematic of a "pistonless" speargun design using a 3 ball sear incorporated in the muzzle, similar idea to the Technisub "Drago" in terms of a remote trigger pull rod operation moving the 3 inox balls in and then out of the annular groove in the front end of the spear shaft to first cock and then release the spear from the gun. Now there is a nice image of a speargun shown there, but does this gun exist, or even something like it?

 

[popgun pete]

How a 3 ball sear operates, this one is from the "Drago". The outer collar releases the balls to move radially outwards for the shot, the smaller inner collar controls the position of the balls in the three slots in the muzzle that the balls roll along as they change their position during muzzle loading and shooting. The balls are exposed to the water that the gun is operated in, so they need to be rust resistant or they will lose their smooth surfaces which are essential to the effective operation of the muzzle's catch and releasing action.

 

[tromic]

Really nice image! I believe this gun exist:
http://photo.qip.ru/users/som70/115885293/207168204/#mainImageLink

Now I understand how this 3 ball sear operates. On Russian forum I can understand only images, not the text. Google translate is not very helpful to me for correct understanding.

Here is a similar ball sear:
http://som70.users.photofile.ru/photo/som70/115885293/xlarge/212489387.jpg

 

[tromic]

Small amount of water would be transferred into the gun after each loading. Also small amount of air would be taken from the gun on each shot. This could be hardly noticeable by user, except after longer usage and dismounting of the gun. Water transfer happens with all other spear guns having pistons too. That is why is good to change oil in pneumatic spear gun at least once in few years.

 

[tromic]

I have no doubt that Vlanikgun is an excellent speargun. However, good catch more talk about the hunter than about the spear gun. Vladimir are you on this pictures? Have there left any more fish in water after using Vlanikgun? I have milky oil in all may pneumatic spear guns (having pistons) after few years of usage, and it is good to change the oil from time to time.

 

[tromic]

The Good catch, this proof of the no-failure operation of the handgun...

Vladimir, which type of sealing do you use in Vlanikgun, A) or B)?

 

[popgun pete]

I tried to see how the sliding control sleeve for the balls operates, but have some various problems circled in red such as inner spring becoming coil bound and not understanding how inner green control sleeve is manufactured to fit inside burgundy outer cover with interlocking flange as shown, but of course I may have made errors in shifting the various parts around. Design seems complicated for what it does, small pivoting lower catch freed by withdrawing trigger pull rod is in a sense another sear tooth, note the tooth is angled so that the force from the cocked spear pushing the front outer hub forwards forces this catch open once it is freed at the rear end. Nice looking diagram though.

Note upper diagram is original, lower diagram has been manipulated to show movement of muzzle sleeve.

 

[tromic]

But that in her good?
This handgun never will know the taste of fish...

I could not agree Vladimir. Maybe Vlanikgun is better, more reliable, more simlpe, but this is also a nice speargun:



Can you answer my question, please?
Можете ли вы ответить на мой вопрос, пожалуйста?

http://forums.deeperblue.com/threads/pneumatic-speargun-without-piston.94538/page-4#post-922892

 

[popgun pete]

But that in her good?
This handgun never will know the taste of fish...

Well I cannot say as I know nothing about this gun, in the West we have no information beyond what we see in that very long thread and the translation is often very obscure in its meaning. No doubt in Russia what is discussed in more easily understood. I resorted to redrafting the trigger mechanism diagram from the image that was referenced here to find out more, but the existing gun seems to be different in the muzzle compared to the one in the drawing. We are just interested in the design and if it works, not in terms of it being competition for your own gun. There are many variations on a theme, I am interested in design rather than who thought of an idea first and like to see these variations even if the ideas have been used before, but in different combinations. There should be room for many variations in the market, but the guns have to work and be reliable over a reasonable period.

Maybe you can tell us more as you have a great deal of practical experience with your own guns.

 

[popgun pete]

Why is the spear so long in the more complicated gun? I have no name for it, so can only refer to it by that term. Your own web-site is not working when I last checked, so no real way to examine later developments only partly seen in a few photos of your "Vlanik" guns. Many people here use Mares, Cressi-Sub, Seac-Sub and Omer pneumatic guns, all variations on a theme, but can appreciate other weapons. I don't think of speargun "brand" ownership as a tribal bonding of like-minded individuals, people can use whatever they like as long as it suits them. That is why I never try to persuade others to buy a particular gun, but want as much factual information as possible so that any decisions made by each individual are based on the relevant information, including observations on any design features which are clearly defined rather than marketing "spin".

 

[tromic]

Вот так работают ружья С.О.М.
Когда он приходит в бассейн, все держатся от него подальше...
<iframe width="420" height="315" src="//www.youtube.com/embed/N2cHYgRkWxU" frameborder="0" allowfullscreen></iframe>

It was long time ago, before 6 years. I believe S.O.M. spear gun is better today than it was before. Such dangerous situations could happen with any spear gun, any day. This situation on video was latching problem, but the gun was shooting powerful.

 

[tromic]

Vlanik, I like your very simple design of "Vlanik" speragun.
Can you tell us which part of the Vlanik speargun is your original design, not copied from somebody other? Is that the concept of piston-less design speargun, shaft tail cup, air inlet valve, line release?
I am sure you were not the first who used that type of latching mechanism on speargun.

 

[popgun pete]

This thread seems to have lost some posts this morning!