Seawolf "Velair": Another pneumo-powered Arbalete

[popgun pete]

Looks like there is another speargun that is similar to the "Dreamair" and that is the Seawolf "Velair". Seawolf make inverted rollerguns, so this looks like a venture into new territory for them. I don't know much about it and have not found out anything about its innards yet, but this photo gives you some idea of the layout.

Actually I don't think this is it, as it has the wrong handle and the "Velair" is more likely this gun.

 

[popgun pete]

The "Velair" grip handle machined in Delrin. (from the Seawolf Spearguns website)

 

[popgun pete]

Looks like this is the gun discussed here earlier this year.

New Pneumatic Powered Cable Gun Design

This design was revealed to me recently by a contact, but I do not know who originated it. At first glance it seems to be a novel way of circumventing the problem of running a cable drive across a pressure boundary in a pneumatic speargun. Some time back we saw a patent for a Mares based cable...

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Garpun.spb.ru :: Просмотр темы - Пневматический роллерган

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[popgun pete]

Apparently some of these pneumatic powered Arbalete ideas date back to 2012, but were then using a sliding telescoping barrel section which releases under air pressure stored in the gun. Here the idea is refined somewhat by having the moving barrel segment now being a piston connected to a long rod which slides inside a small concentric barrel and tubular air reservoir system buried in the gun body. The advantage of this design compared with the Mares one we looked at some time back is that instead of a wire cable (see fig. 5b) crossing the gun's pressure boundary here it is a smooth rod which travels through a stationary pressure seal. Just what stops the moving rod wobbling when it is extended out of the air reservoir system and the gun is ready to shoot is not clear as it is an unsupported length.

 

[popgun pete]

More photos and a possible schematic, the sub-pulleys being doubled up and running on the gun's lower deck.

 

[popgun pete]

Note that where a vacuum is shown in the above diagram the gun could have this inner barrel tube open to the environment at the front end and then be allowed to flood. However any restriction to blasting the water out during the shot would slow the piston and contribute to recoil if the water was jetted forwards.

As with the "Dreamair" this system only has advantages if the piston's cross-section is large as with larger force levels then available the gun can have inefficiencies and still be powerful. I have read comments that the "Velair" piston diameter is 32 mm from which you need to subtract the cross-sectional area of the sliding rod which connects to the rear of the piston. Therefore the piston mass includes that of the piston body and the rod combined.

It would be possible to have two "pneumatic engines" side by side in the gun, but any discrepancy in piston synchronization could pull the shot off centre with uneven side to side wishbone pull.

 

[popgun pete]

Bear in mind the diagrams shown above just illustrate the principle of operation, they are not intended to be the actual gun layout as the piston diameter would be much larger. Now if the "Velair" piston is 32 mm in diameter then the tank diameter would need to be much larger again to provide a reasonable compression ratio. Most concentric barrel pneumatic guns have a 40 mm diameter tank tube, hence a concentric inner barrel and tank would not leave much annular room for a tank volume with the inner barrel being at 32 mm diameter. That means the tank has to be placed somewhere else or any concentric tank is connected to extra side tanks in the gun. In the "Dreamair" there are side tanks either side of the internal barrel that the big piston slides in, however as the stroke of the piston is related to the spear propulsion length by the ratio of the inner and outer winding drums not all of the inner barrel is swept. That leaves about half of the inner barrel volume to serve as a tank in that gun.

The last set of diagrams show the pneumatic system reversed in the gun when compared with the original Russian/Ukrainian version from the garpun website. That allows the use of the cable and pulley system commonly seen on inverted rollerguns, the band battery being replaced by the pneumatic system. As with the inverted roller band guns the spear propulsion length is double the stroke of the energy storage system and the gearing is thus fixed at 2, unlike the "Dreamair" where the winding drum diameters control the gearing which provides some flexibility in designing the gun as to its internal drive system. For example the first alloy "Dreamair" prototype guns had no side tanks, the number of turns of the winding drum axle unwound different cable lengths for the outer cable wishbone and the inner cable connected to the sliding piston.

Ultimately the devil is in the detail, so it will be interesting to learn how the "Velair" arranges its internal components to accommodate the demands of compression ratio, start pressure and spear propulsion length in the gun.

 

[stefpix]

What would be the advantage over a traditional pneumatic speargun? It seems to make a simple mechanism more complicated.
I like the pneumatics as I can attach a camera at the tip of the speargun without showing much of the gun itself.

 

[popgun pete]

The basic advantage is two handed loading and no muzzle loading. Although muzzle loading is relatively easy once you have had some practice, at times people have had narrow escapes when they lost control of the spear tip, often due to stupidity in using a faulty loader. I remember a case where a guy used a tin can and got shot in the head when the tip pierced the bottom of the can. Also there is no problem with band deterioration and cuts which require band replacement. Most band gun users manage their bands and know when to replace them depending on their gun's workload, but it is something you have to prepare for. By way of contrast a pneumatic speargun can go for years without having to do anything to it except washing it after each dive.

The power of these guns can be changed by varying the start pressure in the gun, provided that you can still load it.

 

[stefpix]

The basic advantage is two handed loading and no muzzle loading. Although muzzle loading is relatively easy once you have had some practice, at times people have had narrow escapes when they lost control of the spear tip, often due to stupidity in using a faulty loader. I remember a case where a guy used a tin can and got shot in the head when the tip pierced the bottom of the can. Also there is no problem with band deterioration and cuts which require band replacement. Most band gun users manage their bands and know when to replace them depending on their gun's workload, but it is something you have to prepare for. By way of contrast a pneumatic speargun can go for years without having to do anything to it except washing it after each dive.

The power of these guns can be changed by varying the start pressure in the gun, provided that you can still load it.

Thank you. I can see being useful for longer guns. I feel comfortable at loading the Salvimar 65 cm which is actually 70+ cm, on the hip. But not sure with a 85 cm or longer.
the 55 vuoto dry muzzle actually is sufficient to get the shaft all the way througb a blackfish or striped bass skull and get the fish on the line.
but I don’t shoot fish at a large distance.
pneumatics have a reputation of being high maintenance.
I just add some drops of oil each year. I had once to replace the dry muzzle gasket.
I started spearfishing in April after the winter pause. Initially I found the piston was a bit sticky and hard. when loading i depressurized, added oil, and loaded / unloaded without pressure in the barrel, it got smooth again. For pneumatics I like the simple design. I load in the water parallel to the surface, with the gun pointing clearly away from my face

 

[popgun pete]

All pneumatic spearguns if they are not used for a very long time can suffer from piston jamming as the piston seals temporarily stick to the bore of the inner barrel. It can then require a big effort to budge them, but once they get moving again the problem disappears and you are back to normal. Rather than force it you can let some air out to reduce the gun's pressure and then the piston will free up very easily and then you can restore the pressure to what it was before. The larger diameter of the piston in these pneumo-arbalete style guns may be even more prone to sticking, however it will only require a pull on the wishbone periodically to keep the piston moving freely and the spear does not even have to be in the gun.

 

[popgun pete]

Another image of the barrel.

Where the air pressure is added to the gun with a screw on hose fitting?

 

[popgun pete]

Spearing fish with a Velair 95.