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Taimen - Russian pneumovacuum speargun

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.
Although I don't bother with aligning the spear shaft to have the same orientation in the cocked gun by rotating it to have the flopper on top (or underneath if that is your preference) in the pursuit of improved precision at longer shooting distances, there appear to be some pneumatic speargun users who do. The use of single flopper, integral tip spears does create some axial asymmetry and on any long shaft there can be a slight bend even though they appear to be straight, hence for the sport of underwater target shooting such shaft and flopper alignment considerations are taken into account. There is a discussion on the subject by Victor Doroganich which details speargun preparation for these competitions. You can read it "on-line"; I don't remember the link, but a search will find it.

It occurs to me that a gun such as the "Taimen" allows the cocked spear to be rotated simply because the spear is not jammed into the face of the piston, instead it is held in the gun by the vacuum in the inner barrel and can even be pulled forwards slightly to check the vacuum before the spear is sucked back into position. Thus the piston tail, when engaged by the sear tooth, is not going to be rotated by turning the spear with the gun cocked to shoot, whereas in most other pneumatic spearguns it will be unless the spearguns are of the releasing valve type as their pistons are not held by a sear lever.

Maybe this decoupling of the spear tail at the piston face could be utilized in other vacuum barrel spearguns which do use single flopper, integral tip spears if you want to twist the shaft to maintain the same rotational orientation of the shaft in the gun for every shot. That would then eliminate the possibility of misfires caused by shaft twisting which can disengage the hooking action of the sear tooth on the piston tail.
 

I think that such a solution is more appropriate for shorter and thicker shafts used in rivers and lakes.
With longer shaft, precision and power of the shot would be affected.
 
Maybe you could elaborate on why that would be as the extreme shaft tail would be a cylinder rather than a taper, but otherwise nothing changes.
 
popgun pete said:
Maybe you could elaborate on why that would be as the extreme shaft tail would be a cylinder rather than a taper, but otherwise nothing changes.
Click to expand...
I think that the shaft has much better support in a cone tail end and cone in a piston thus being better aligned and supported by the piston what makes bending of the shaft during acceleration lesser. Oscillations of the shaft continues during the flight of the spear through water taking of its energy and precision.
 
Well the tail still sits in the centre of the piston face as the cylindrical rear end, or peg, fits into a hole the same size as the peg, but with a tiny clearance so it does not jam in place. The main limitation would be if the spear was too heavy to be supported by the vacuum opposing the spear falling out of the inner barrel. I remember working out the figures for the shaft diameter and mass versus the supporting effect from the vacuum in an earlier post which is probably on this thread. That was for at the surface, but the deeper the gun is submerged then the more external pressure there is to support the shaft. The longest "Taimen" is a 1200 mm, although it may have been a "special" as I don't recall it being listed in their catalogue, but it appears on the gun dimensions table. Given how "Taimen" measure their guns it would be a 1150 mm if you remove the length of the raked handle.
 

I think even the tiny clearance is acceptable only with shorter and thicker shafts, especially if the shaft tail does not go deep (12-13 mm) into the piston. I saw on Russian forum, in some cases the shaft tail goes very shallow into the piston, but they use 9 mm shaft maybe 60 - 70 cm long. If the piston is also short like in case of Taimen a long thin shaft would not be prevented from bending inside the barrel during acceleration. Well, this might not be of significant influence, or maybe could be? It would be interesting to investigate this using high speed camera, using cone tail, and not cone tail of the shaft.
 
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I doubt that bending of the shaft has anything to do with the spear tail being jammed in the piston or otherwise. In fact pneumatic spearguns of the forward latching type have pistons that only push on the spear as they rely on the sear tooth at the muzzle to hold the spear in the gun, hence the piston cups the spear tail rather than grips onto it (e.g. Technisub "Drago"). If the spear bends in the barrel of any pneumatic speargun then it is just the result of the instantaneous loading up of the spear which is basically a thin metal column, similar to the bending or bowing effect you see when you muzzle load the spear into the gun if it has a lot of air pressure in it. The jamming of spear tails using conic friction or spigot mounted ball gripping arrangements is all about stopping the spear from falling out of the cocked gun and has nothing to do with stopping the spear bending under acceleration. That is the job of enclosed tracks that fully encircle the shaft, the less clearance for the spear then the more effective they will be, but then the spear may briefly rub on the inner barrel wall, however I have never seen any obvious signs of that happening, although it may occur in hydropneumatic guns (e.g. 8 mm spears in 9 mm inner barrels). The maximum amplitude of any transient bend is at the mid-point of the shaft which is moving with respect to the gun's inner barrel as the spear leaves the gun.

Although we cannot see it I suspect that very slim spears at longer lengths do bow inside the bore of an inner barrel when being driven up to a high velocity, but the centralizing washer and the close fit of the muzzle help to minimize or dampen any effects as the spear leaves the gun and the piston pushing hard on the spear tail immobilizes it with respect to the piston. If you think about it the spear tail to piston connection is transmitting all the propulsive force to the spear, so relative movement there is next to impossible as the acceleration pushes them tightly together.
 
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That is a case I am talking about, slim longer lengths spears. Acceleration in pneumatic spear gun is about 700 m/s2 (gravity is 9.81 m/s2). I believe that firm grip between piston and shaft is beneficial and could dampen eventually bending.
 
tromic said:
That is a case I am talking about, slim longer lengths spears. Acceleration in pneumatic spear gun is about 700 m/s2 (gravity is 9.81 m/s2). I believe that firm grip between piston and shaft is beneficial and could dampen eventually bending.
Click to expand...
Well we have to disagree on this one as I don't see how that would work from a mechanical viewpoint. Holding a long thin rod at its rear end will not stop it from vibrating. I think this vibration of a shaft in a pneumatic speargun is a non-problem anyway and not worth worrying about. The mid-point of a shaft is free to move laterally even if the ends are fixed, hence if vibration amplitude was large enough to pose a problem then that movement would need to be confined by having a close-fitting inner barrel.

An example of an unsupported spear that may vibrate is in the piston-less spearguns like the "Vlanik", but there the spear moves through a longer guide tube in a very close fitting muzzle which may suppress any vibration as the spear emerges from the gun.
 

Regarding "Vlanik" example I disagree! That type of speargun is free from this kind of vibrations because the air pressure does not act on the shaft end like in guns having piston.
I have an idea how would be, maybe, possible to test how high is a bowling of the shaft. I would place the shaft perpendicular to the floor and put some weight on the other end of the shaft. Under the weight the shaft will bend. The question is how much weight should be used to have same condition as the shaft has in spear gun on shot? I suppose 1/2 of force necessary to load the spear gun because the center of the mass of the shaft is on 1/2 of its length. What do you think about this Pete?

Here is a difference between two cases we were talking about:



b) has less bending than a)
 
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In a "Vlanik" speargun high pressure air still pushes the spear out of the gun, it is just acting over the cross-section of the spear at the rear end as the projecting front end of the spear only has ambient pressure air opposing it. Pressure effects inside the gun cancel out as the forces radially directed at the shaft's cylindrical surface all oppose each other. Spearguns with inner barrels have a sliding piston functioning as a force transmission element that does the same job, the main difference is the piston is usually of a larger diameter than the spear and transmits all the force from the high pressure air acting on its rear face onto a smaller cross-section on the spear tail where the spear and the piston's front face actually make contact with each other. Therefore the contact pressure at that connection position is higher than that on the rear of the piston (as less area is involved) and ideally the effective centre of this force application area remains constantly on-axis with respect to the inner barrel during the gun's shooting operation. That may not be the case if the piston can tilt slightly when moving in the inner barrel if the spear bends under the rapid loading and forces the piston off to one side. To prevent that from happening pistons are usually long with seals or rubbing contact surfaces spaced far enough apart that the piston cannot tilt appreciably in the inner barrel. Even with a "conic friction" spear tail socket connection a piston with a single seal, or closely grouped set of seals, can still tilt in the inner barrel if the piston is relatively short. I have had guns momentarily lose some air pressure during muzzle loading with the shaft about half-way into the inner barrel as the piston seals lost contact for an instant, then resealed again. Later inspection showed no damage to the cup type seals used in that gun, but they were of the "back to back" type, so they were situated very close together, being a single rubber moulding. Thus the piston could rock slightly in the inner barrel bore unless you pushed absolutely straight down on the hand loader, which is not always possible.

How much energy ends up in bending a spear I do not know, if it happens then it will contribute to one of the energy losses incurred during the gun's shooting operation that do not transfer to projecting the spear from the gun. Maybe you could place the spear on a weighing scale and push down on it until you see it first bend, then check the force level being applied. If you push on a slight angle then the spear will bend more easily, so you need to control the direction of the load being applied, maybe easier said than done.

The length of the shaft tail embedded in the piston is negligible with respect to the overall length of the shaft, the longer and thinner the shaft then the more susceptible it is to bowing, but the shaft bowing may tilt the piston if the latter is not firmly held by the inner barrel bore contacting at either end of the piston body. The high loading between piston face and spear tail during the shot will keep them tightly connected together, however that contact may move around with respect to the inner barrel axis as one follows the other with the piston able to tilt. If on the other hand the piston cannot tilt, then it will hold the spear tail centralized in the inner barrel bore, but it will not be able to control flexing of the shaft forwards of the piston until the spear travels far enough through the muzzle that the unsupported shaft length, in the lateral sense, has shortened to the length where a curve in the shaft cannot be sustained.
 
When the spear also serves as the propelling element, which is exposed to chamber pressure, then the chamber pressure needed is much higher as pneumatic spearguns don't shoot spears which are the diameter of sliding pistons (usually 11 mm up to 14 mm), but they do use spears which are from the upper range of diameters, such as 9 mm and 8 mm. Hence the thicker spears used in "piston-less" spearguns such as the "Vlanik" and the "RPS-3". Very high chamber pressures can compensate for the use of smaller diameter spears in such guns, but that requires a big pumping effort to produce the necessary pressure level inside the gun. A small diameter receiver or tank reduces the number of pump strokes required, but you still have to be able to push the pump handle down once you reach the required pressure level inside the pump body in order to transfer air across into the gun.

It is interesting to note that the "Taimen" is offered with a 10 mm diameter inner barrel for shooting 6.5 mm and 7 mm diameter spears and an 11 mm diameter inner barrel for shooting 8 mm diameter spears. I suspect that inner barrel diameter change is because the shaft mass increases by 30% when you move from a 7 mm to an 8 mm shaft for spears of the exact same length, hence the force acting on the piston needs to increase in order to obtain the same level of propulsion using a heavier spear. Moving from a 10 mm to an 11 mm diameter inner barrel will increase the force level by 21% as that is the increase in cross-sectional area of the larger piston, however to attain an increase of 30% would have required an inner barrel of 11.4 mm diameter. As the "Taimen" relies on a lightweight piston with low sliding friction this must have been seen as an undesirable size increase and the gun's compression ratio would have gone up further as well, so the decision must have been made to only increase the inner barrel bore to 11 mm. It is this aspect that made me choose the 7 mm shaft version when I purchased my "Taimen", plus I already owned other pneumatic guns that shoot 8 mm shafts.

On a practical note the availability of stainless steel tubing in the bore sizes required may have influenced the decision as to which inner barrel diameters could be used.
 
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The "Taimen" guns are now supplied with the 2-part front hub as standard equipment after the successful completion of field testing with the new muzzles which allow the muzzle vacuum cuff to be replaced without depressurizing and dismantling the gun.
 
In addition to the detailed explanations that Pete provided to the community, here are some vids on the assembly and disassembly of the gun.

I know it's in Russian, but I haven't found any video in English yet.

Good viewing

1. 2. 3. 4.1 4.2
 
Interesting to see videos for the most recent version of the “Taimen” which is now always equipped with the 2 part hub or muzzle which allows a rapid replacement of the muzzle vacuum seal by simply unscrewing the front section of the muzzle (or hub) with your fingers. To some extent this updated design has reduced the need for the “Taimen” special tool as the two semi-cylindrical short prongs on one side of the glass reinforced black plastic tool were previously used to insert into a set of diametrically opposite holes in the front end of the muzzle in order to unscrew the single-piece muzzle from the gun. Now that the front section with the multiple forward facing holes unscrews very easily this part of the tool is not of any real use, but something needs to replace it as in order to remove the remaining rear section of the muzzle from the gun some other hand tool has to key into the transverse slot cut into the face of the threaded metal boss which supports the rear of the rubber vacuum seal. A thin plastic washer interleaved between them provides support for the rubber seal where there are gaps on either side created by the presence of the slot in the metal boss, so you don’t want to lose that plastic washer. In the second last video we can see the shaft of a screwdriver blade being used for this dismantling purpose as the length of the screwdriver also provides the necessary leverage at each of its ends to unscrew the rear part of the muzzle, plus the screwdriver shaft is hard enough to resist the high contact pressure created by the slot being positioned radially closer in to the longitudinal axis of the gun than the ring of holes were in the front of the single-piece muzzle (same torque applied closer in increases the force on the engaging surfaces).

I had wondered if the “Taimen” special tool would be modified or an adaptor made to make use of either the two existing prongs or the wrench jaws on the opposite side that are now used to remove the line slide holder. Maybe a short metal key that engages the transverse slot and either of these two features of the special tool simultaneously while eliminating any rocking between the two pieces in order to achieve the stability of the original set-up which worked very well.
 
There are now single flopper “Tahitian” style spears available for the “Taimen” pneumovacuum speargun in addition to the detachable screw tips with double flopper shafts and the double short flopper, fixed tip spear shaft that came standard with the gun (or it used to be, as things may have changed since I purchased my gun). I have never used the latter as its four-sided, fluted needle tip would not survive a collision with the rocks that strew the areas where I have used the gun, especially those lurking just out of sight under the sand and weed cover. What is interesting about the new integral tip “Tahitian” spears is the shank rearwards of the polyurethane spear stop for the slider (or line slide) is now much longer than it was previously (see attached spear photos).

The service life of the “Taimen” vacuum muzzle seal is prolonged by inserting the spear tail strictly axially rather than at any slight angle. The slider already being locked into the front of the muzzle via the metal holder screwed into the front of the muzzle assures this alignment before you start pushing on the spear with any great effort. However you can see from the attached inner barrel bore cleaning diagram detail (I have now added the original muzzle) that the slider can be locked into the holder with the spear tail’s rear end spigot well clear of the piston face and that the separation distance between them, A and B respectively, has further increased when comparing the original muzzle with the now standard two-part hub or muzzle. While there is no problem with short spears I expect that longer and thus heavier ones dangling out from the muzzle before applying any real loading effort may put a load on the slider making it not so easy to push it back to lock in place before the spear tail has slid right inside the muzzle bore. Possibly the now longer rear shank places the spigot in the piston before the polyurethane bush has pushed through the muzzle seal, but I have not done any measurements to check it out. The holder “locks” the slider by virtue of the “O” ring trapped inside it engaging the small groove seen in the rear section of the slider (see inset on spears photo). The grip of the “O” ring is not very tight as the spear has to knock the slider free of the muzzle with the shot. A longer rod has less clearance to wobble in a confined tubular space than a shorter one, in fact pneumatic speargun pistons were made longer to stop such wobbling or tilting in inner barrel bores, hence the long forward projection on the piston nose in front of the seals. The same reasoning may apply to these longer spear tails as a better aligned polyurethane bush will stretch the muzzle vacuum cuff more evenly than if it was biased off to one side and (the bush) being temporarily squeezed out of shape on that side.

There is also a removable tip “Tahitian” option where the sharpened end is a screw-on piece that can be replaced on the flopper equipped shaft, a system that “Nemrod” in Spain used on their pneumatic speargun spears many years ago and also employed by other manufacturers as the sharp tip can sometimes be smashed beyond repair without any other damage to the spear whatsoever. A problem with integral tip shafts is that repeated sharpening repairs can whittle down the tip towards the pivot hole for the flopper pin (that is if the shaft stays straight for long enough), hence the need to stay away from rocks unless you can replace the tip.

These “Tahitian” spears are available in 7 mm and 8 mm diameters to suit the range of gun lengths.

 
I thought that I would draw it up to see what a relocated polyurethane bush would look like, however this is just an estimate on my part.
 
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