Aquatech "Dnepr" hydropneumatic speargun

Ciao Pete , mi dispiace per il furto.....meno male che quel giorno non avevi il Mar Nero in macchina ....il pezzo sarebbe meglio farlo in titanio ,più resistente all'acqua marina .Ciao Efisio

Ciao Jegwan , potresti smontare la valvola che viene azionata dal grilletto per vedere come sono i pezzi di cui è fatta e mettere le foto ? Grazie in anticipo .....Efisio

The "Aquatech" guns have used different trigger control valves over the years. In the early guns the control valve operates like a swinging blade shutter with a small outlet hole in it, in my "Black Sea" gun it is a downstream valve where the trigger system mechanically blocks the valve from opening outwards with pressure acting behind it. In the later versions of the gun the control valve is an upstream valve where pressing the trigger pushes a valve stem inwards against the pressure inside the gun.

Using 100 Bar of air pressure to obtain the high power shooting performance you don't want any errors in the construction or the gun will be very dangerous if you build it as a "Black Sea" type gun without doing extensive testing of its components. The "Aquatech Black Sea" guns underwent a lot of development before being sold as limited production guns.

Grazie Pete , per costruire la valvola del grilletto ho prima parlato con un ingegnere idraulico spiegandogli per cosa mi serviva la valvola e lui mi ha consigliato al meglio e già a 50 atm funziona benissimo , lo sfiato dell'acqua va in avanti e gli spessori usati per costruirla reggono sino a 450atm .Grazie per i tuoi consigli ......ti chiedo ancora se mi puoi dire quanto misura il diametro del pistone della pompa idraulica del Mar Nero .Grazie della tua disponibilità .....Efisio

From memory the hydraulic pump piston is 8 mm in diameter, it is currently assembled and I am not going to dismantle it again to find out. You should read the “Black Sea” thread as this info should be there, plus I no longer have my technical notes available on a computer file as I did before. I suggest that you use a translator such as http://www.bing.com/translator/ to post in English otherwise others here will not know what you are saying.

The hydraulic pump operates by using a metal rod, which acts as a piston and displaces water inside the hydraulic pump body as this rod slides past a stationary “O” ring seal located at the entrance to the hydraulic pump or “hydropump” body. Hence the volume of the metal rod which has moved past this stationary seal determines the water volume pumped with each stroke of the “hydropump”. Thus rather than a pump body bore acting as the dynamic sealing surface for the pump it is the smooth surface of the inserting rod that performs this function.

A system of levers provides the necessary mechanical advantage when operating the “hydropump”, although the equivalent “bore” of the rod (8 mm) compared to the inner barrel bore (9 mm) provides some force reduction as well when loading/cocking the gun with the “hydropump”. The design of the “hydropump” connection and its fabrication detail is the main aspect of the “Black Sea” design from an engineering viewpoint, but this you will have to work out yourself as I am not going to encourage the cloning of a gun which is patented.

Grazie Pete , l'ydropum che ho costruito io ha il pistone da 10mm , lo speargun che sto costruendo sfrutta solo il principio del funzionamento hydropneumatic ma la forma e l'aspetto sarà completamente diverso , in anticipo l'hydropump sarà inserita sul manico , quindi nascosta . Scusa se scrivo in italiano , ma non so usare il sistema di traduzione . Ciao Efisio

Jegwan said:

Here's a small 35cm "Dnepr" speargun made by Aquatech, S.F. Kravchenco in Ukraine April 2010.

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popgun pete said:

I have not thrown away the broken pieces, but a recent burglary resulted in my digital camera being stolen, as well as my notebook computer and some other items. Right now I am using a borrowed computer, in fact I have only managed to get back on-line in the last couple of days. Unfortunately no more photos until I can buy a replacement camera. I will probably use aluminium to make the parts as stainless steel will be too heavy.

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Thanks for posting Jegwan... looks fantastic with its Yakov (James) Bond styling... if it doesn't float anyway why did they make the trigger and line release in plastic?.. they'd be ideal candidates for 3D printing in stainless steel and very simple to design? Weight would be negligible between Ally and SS surely?

The downstream control valve in my gun needs to open rapidly or the shot will be throttled if the releasing valve (which plugs the rear of the inner barrel) cannot push back the required volume of water through the small bore transfer pipe to enable it (i.e. the releasing valve) to open fully. The sliding and rotating parts that oppose the control valve opening were made from plastic to enable them to be pushed aside virtually instantaneously, or that was my assumption. Injection moulded parts are unusual in guns from that part of the world, normally everything is made from metal, so the plastic items found there were a bit of a surprise, plus they had been adjusted by subsequent filing to make them work properly. How much heavier they can be made without affecting the performance I don’t know, but their rubbing friction also needed to be very low as the cam turning action of the line release plate is marginal at best due to the geometrical alignments imposed by the space available in the twin parallel plate grip handle frame. When I unwittingly impeded the swinging of the line release lever which had only cracked the sliding link initially I noticed that the shot was significantly reduced in terms of forcefully ejecting water from the gun. That was the first thing that I actually noticed and being concerned that something was then amiss I recharged the gun and on about the third stroke of the “hydropump” I heard the control valve start hissing as the sliding link snapped completely. I then realized what had happened without even looking, so it was no surprise when I dismantled the grip section to discover the broken part. I assume that the design was changed in the later guns as although a power operated line release opening action seems a good idea, internal parts can be damaged if the lever cannot move freely.

Definitely seems like a bit of a weak spot... I was assuming the part broken on your gun was similar to the line release plate above Pete? Square peg to fit a round hole comes to mind... would it be possible to slightly round the edges of the handle peg which the line release plate fits onto and then cap/crimp/bond it in a rounded metal sleeve somehow. You could then have all the trigger parts 3D printed or make them yourself in Ally or SS to the exact size... including the new, perhaps slightly larger but rounded diameter of the modified handle peg (less friction)... hopefully stopping it from happening again? Let me know if I'm talking rubbish...

There is only a slight similarity in the shapes, in my gun the line release plate is longer in the fore-aft direction and the trigger peg fits upwards into an opening, not a notch, as the cam shape that controls the shooting action is located on the rear edge of the plate, behind where the trigger holds onto it. The line release plate swivels on a metal pin mounted on one side of the metal handle frame in my gun, not a square plastic peg as shown in that photo. I posted photos of that area of the handle on an earlier thread, although I never showed the sliding link, but you could see the metal cylinder of the control valve which travels in a rectangular slot in the handle frame to push the link forwards. The link moving forwards rotates the line release plate and the gun shoots.

Here is the ancestor to the “Dnepr”, the Aquatech 500A, the letter designation “A” indicating a rear handle. The guns came in different handle positions as it was possible at the factory to lengthen or shorten the small bore transfer pipe that connected the trigger valve (a “pilot” blade or shutter valve) in the grip to the hydraulic locking chamber at the rear which held the main releasing or firing valve. In the “A” model you cannot see the transfer pipe as it is entirely hidden inside the handle frame, while in a “B”, “C” or “D” model you could see the pipe emerging from the rear of the grip, the “D” model having the grip handle right near the front. After my discussions with Sergiy Kravchenko he decided to change the handle to incorporate a safety or trigger hold down lever so that you could flood the gun with the trigger valve open, but with your finger not actually on the trigger, something that was very handy on the longest “Magnum” guns that were well over a metre in length, from memory being 1.5 metres or more. Originally 80 cm had been the longest Aquatech gun, but short stroke pumping/accumulated loading meant that you could muzzle load the longest guns by say repeating a 10th of a barrel stroke 10 times on a nearly fully inserted spear which would give you full powered travel in the barrel. Or if you were a glutton for punishment 20 short strokes or 30 short strokes if you put your back into it. Needless to say even with the inherent inefficiency of hydropneumatic guns the spears departed the gun like a rocket as you inexorably pushed up the gun’s compression ratio. Biggest problem is the Aquatech guns don’t float after the shot, they are absolute sinkers unless retrofitted with a big timber flotation stock (some were and looked like a giant sniper rifle as a result with a 30 mm OD barrel sticking out the front end). The shooting line supplied with my gun was a form of mono that was a nightmare for tangles and I soon replaced it, however I kept it and you can see the gun here virtually as it arrived back in 2000. Although captioned “cocked to shoot”, the gun has no water in it and is actually uncharged even though this is what it looks like when ready for action. Afraid of losing it if I dropped it on a weedy bottom on a surgy day where kelp whipped back and forth and buried anything in seconds I soon stopped using it, however the idea for the “Black Sea” auxiliary pumping barrel gun (based on the Alcedo “Hydra”) was forming in my mind and Sergiy soon began making those guns based on this original handle shape, although the actual “Black Sea” name was to come much later.

I just checked and the Aquatech gun handle position page is still up, only there is no longer a "D" version for "up close and personal" shooting in very murky conditions:
http://aquatech1.narod.ru/english3.html

While looking through my recovered files I found the instructions for these "Aquatech" guns. They are double-sided print on a single sheet of paper, then folded into three sections vertically, rather like a touring map.

I had these guns in repair. Plus - the lack of sound when fired. Cons: 1.Very thin barrel 9mm outer diameter and 8mm inner diameter. Deformed with a large loading force with warp and grains of sand; When assembling, misalignment of the coaxiality of the trunk and the bend of the trunk in the pig tail are possible; 2. The absence of the bleed air valve from the receiver and you have to pierce the injection valve rubber with a needle; 3. The tube valve bypass - start planted on epoxy resin and from time to time leaks; 4. When the trigger is pressed, a shot is delayed due to throttling of water from the valve space through a 1mm opening of the valve;

This gun was completed by me. Put the bleed valve and put the brass clamp on the valve tube with its flared and O-ring seals.

Zahar said:

I had these guns in repair. Plus - the lack of sound when fired. Cons: 1.Very thin barrel 9mm outer diameter and 8mm inner diameter. Deformed with a large loading force with warp and grains of sand; When assembling, misalignment of the coaxiality of the trunk and the bend of the trunk in the pig tail are possible; 2. The absence of the bleed air valve from the receiver and you have to pierce the injection valve rubber with a needle; 3. The tube valve bypass - start planted on epoxy resin and from time to time leaks; 4. When the trigger is pressed, a shot is delayed due to throttling of water from the valve space through a 1mm opening of the valve;

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The air can be released from the gun using a straightened out paper clip with the end smoothed over to remove any sharp edges. The annular rubber ring valve is the same type as that used in the “RPS-3” and until the latter received an air release screw the compressed air had to be let out in exactly the same way by temporarily dislodging the rubber ring at the point directly under the entrance hole. In the Aquatech gun the inlet and outlet valve are one and the same thing and are located at the front end of the gun to keep away from the sliding annular piston inside the gun body. The throttling of the trigger release is of no major concern as you soon adjust for the delay and know when to pull the trigger. I never let go of the gun, so it never hit the bottom, tucking it up under my arm while disengaging its victims from the spear, or clipping it to my gun belt via a cord looped through the handle’s butt. One time I used a plastic buckle of the quick disconnect type that you push to engage and press on the sides to disengage. The buckle was threaded on a nylon strap that was secured to the grip handle by the lower grip cover plate or grip scale affixing screws where there is a narrow rectangular gap either side in the butt of the grip handle, that gap being the same size as the polypropylene or nylon webbing strap. It looked rather weird so I took it off, but was a good way to secure the gun and not drop it.

A few times when I have not used my Aquatech gun for a very long period I discovered that the gun seemed to have jammed when I next filled it with water and tried to muzzle load it. The culprit is the annular piston can stick after sitting without moving for a very long time. This is analogous to the piston sticking in pneumatic guns for the exact same reason. I found the answer was to remove the releasing valve and biasing spring which in any case had just been reinstalled in the gun after it was taken out of storage and then half fill the inner barrel with water. With the innards removed the locking chamber fills immediately with water as there is no valve action to stop it and you then apply a big loading effort on the loading bar using both hands with the gun butt supported on a solid surface. The annular piston will free unexpectedly sending the spear down into the inner barrel which once the spear tail "O" ring clears the open rear end of the inner barrel will send water gushing up out of the gun around the inserted spear and all over you. The water thus ejected will give you a shower, but at least the gun will be back in action. Rather than pull the spear up and out of the muzzle it is easier to remove it by unscrewing the gun's rear cap as the tail of the shaft will have already slammed into the back wall formed by the cap once most of the water departed the gun under pressure. This allows you to unscrew the spear tail and pull the spear out of the gun backwards provided the spear has no tip or you can pull it forwards without worrying about damaging the tail "O" ring on the exposed rear edge of the inner barrel.

These heroics can be avoided if your gun has an air release screw as you simply let most of the air out of the front tank and then the annular piston will be much easier to start moving. Zahar has incorporated an air release screw in his example which can be seen in the muzzle photo above, some Aquatech guns have it, but most of the earlier guns don't have one. The reason the annular piston can be hard to budge is because there are two "O" rings with the outermost being of a much larger diameter as it slides on the inner wall of the tank tube. Thus after a long period of inactivity you have more “stiction” even if the gun has been stored muzzle up to keep oil sitting around the annular piston. Note that this is the reverse of pneumatic guns which need to be stored muzzle down to keep oil sitting around their pistons.

The O-ring of the piston squeezes out oil and comes into contact with bare metal during long storage! At the same time, the rubber of the O-ring sticks to the metal and the first movement breaks off pieces of rubber!
I have been working with valve guns for over 30 years and I know very well the problem of static friction! Found a solution in the use of bronze powder as an additive in gun oil! During the operation of the piston, bronze adheres to the O-ring at the point of contact with the metal during friction and reduces friction to a minimum!