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Alcedo "Hydra" hydropneumatic gun

popgun pete

Well-Known Member
Jul 30, 2008
2,952
571
153
Australia
The Italian Alcedo "Hydra" was the first hydraulic valve operation hydropneumatic speargun. It probably inspired a number of other hydropneumatic guns, but most of those used a sear tooth to directly hold onto the spear shaft rather than the patented hydraulic valve system in the "Hydra" which utilizes a "hydraulic locking chamber" to control water flow inside the gun, so these other hydropneumatic guns are not much different in operation to a standard pneumatic gun. You push the spear into the gun and the mechanism clicks as the sear tooth engages the spear shaft tail, there being no sliding piston inside the inner barrel of a hydropneumatic speargun. Some simpler construction guns engaged the spear shaft at the muzzle end, being forward latching spearguns, the shaft carrying a notch at the front end just behind the speartip, which weakens the spear.

Some years ago I pulled a long non-operational "Hydra" speargun apart to see what was inside and to discover how it worked, you can read the results here along with the many detail photos of the gun's innards. http://aquatech1.narod.ru/eng17.html

The accompanying article is a compilation of an original 1964 review of the "Hydra" gun and e-mail conversations with Sergiy Kravchenko, but some of it has been edited out, so the question has to be implied from the answer in some cases where the question is missing. The reason for the article being placed on the Aquatech web-site is that the "Hydra" speargun's operating principles were the direct inspiration for the subsequent "Black Sea" speargun developmental work (the "Black Sea" name came much later), although the layout is very different in the latter to produce a much more compact weapon for underwater hunting. The "Hydra" speargun's rubber bladder (located inside the blue anodized bulbous rear alloy tank) is an odd arrangement by today's standards, but it's use fitted in with the general appearance of the big carbon dioxide guns of the time (early to late sixties). It is interesting to note that if you reconfigure the heavy vented metal grille that separates the air filled and hence pressurized rubber bladder from the forward flooded sections of the gun by turning the grille into a pierced wall metal tube and wrapping the bladder around this tube in the form of a rubber hose you obtain the system used in the "RPS-3" hydropneumatic speargun. This space saving arrangement means that the pressurized air reservoir can now sit around the inner barrel instead of sitting directly behind it, but if you have the air reservoir forward of the gun's grip handle then you cannot use a hydraulic locking chamber design because water flows directly onto the spear shaft through the many holes in what is now the inner barrel of the gun. So the gun needs a mechanical sear tooth mechanism and a seal at the muzzle around the spear shaft to keep pressurized water inside the inner barrel, a very unlikely arrangement, or the rubber hose covered vented metal tube has to be restricted to a rear tank behind the gun's trigger mechanism (such hydropneumatic guns have been made, but they will not be discussed here).

Later hydropneumatic guns, such as the "Aquatech" and "Zelinka" models, replaced the rubber bladder/rubber hose flexible partition on the air reservoir with an annular piston sliding on the exterior of the inner barrel tube instead, but the "Aquatech" guns retained the "hydraulic locking chamber", although it was a much more compact arrangement than the large skyrocket shaped valve used in the "Hydra". Note that the bore of the hydraulic locking chamber must always be greater than the bore of the inner barrel or the system will not work, the lowest pressure has to be to the rear for the trigger or releasing valve to open rearwards and unplug the inner barrel once the rear section of the chamber is depressurized by opening the gun's trigger control valve.

As for the "Hydra" push-pull rear mounted hydropump, this is how it works. The hydropump's inner pump rod carries a cup type rubber seal, not unlike the one on the spear tail, that pushes water on the pumping stroke and temporarily collapses in on itself on the return stroke, thus allowing the pumping barrel to suck in water past the rubber cup seal for the next pumping stroke when the cup seal will flare outwards to again seal tightly on the pump's inner bore. The spear can be pumped in the front barrel in exactly the same way, but there the bore of the "pump" is larger, so more effort is required. A non-return valve, on this particular gun a thick rubber flap, seals the hydropump's small outlet hole inside the gun's flooded centre section thus preventing the building water pressure inside the gun escaping by pushing the pump handle backwards. Just as well, because the hydropump pump handle would hit you in the face otherwise!

There is a later version of the "Hydra" with some plastic parts and a more elongated appearance with respect to the rear tank which seems to be an even bigger gun than the original, but I have never located one in order to dismantle it. Collectors usually don't want to risk damage to their guns, but of all the speargun types you really need to open up hydropneumatic guns as saltwater can do nasty things inside the gun if you don't clean them out.

The "Hydra" shown here looks like it was washed out, but the original owner never flushed out the hydraulic locking chamber or the hydropump, the two most critical areas inside the gun and so it finally seized up. Aluminium oxide and fine sand particles spilled out of the hydraulic locking chamber once it was freed, but the hydropump is well and truly seized, so the gun is out of action. I suspect that the thick rubber bladder would split if recharged with pressurized air today, rubber product's lose their strength over time and any spare parts like a rubber bladder would be non-existent after all these years.
 

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popgun pete

popgun pete

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Jul 30, 2008
2,952
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Australia
The link works if you remove the prefix added for some reason by Deeper Blue -wlmailhtml:{B2C17DA8-1348-4132-8B1F-A3D46D708B45}mid://00000037/!x-usc:http://aquatech1.narod.ru/eng17.html
 
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Stephan Whelan

Papa Smurf
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Hi,

The bit you are referring to: wlmailhtml:{B2C17DA8-1348-4132-8B1F-A3D46D708B45}mid://00000037/!x-usc:

Is not being added by DeeperBlue.com - it is most probably due to where you copied the link from (most probably an email client or hotmail/gmail type website) and that is adding that erroneous code.

I have edited the original post to remove that from the problem.

Thanks!
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,952
571
153
Australia
Hi,

The bit you are referring to: wlmailhtml:{B2C17DA8-1348-4132-8B1F-A3D46D708B45}mid://00000037/!x-usc:

Is not being added by DeeperBlue.com - it is most probably due to where you copied the link from (most probably an email client or hotmail/gmail type website) and that is adding that erroneous code.

I have edited the original post to remove that from the problem.

Thanks!
Actually I took it straight from the web-site, but thanks for fixing it.
I have noticed this extra code added before, but not on every occasion, it seems to be rather random.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,952
571
153
Australia
Looks like I was completely wrong about the hydropump using a moving cup-type rubber seal mounted on a pump rod sliding inside the inner bore of the pump, but then I could never undo nor open up the hydropump to see what lies inside as salt corrosion has jammed it solid. The hydropump is actually a water volume displacement pump where a long, slim rod pushes through a stationary rubber seal located at the inner pump body's rear end and which is held in place with a metal collar that needs a four pin special tool to undo it. I made such a tool, but it failed to engage the small indentations in the exposed face of the collar well enough to afford a sufficient grip. When the bare pump rod is pulled rearwards out of that stationary rubber seal, the rod has a thin tip at the front end so that the seal then loses close contact with the rod, the pump can breathe in more water for the next stroke through the annular gap created. It is a bit like filling a glass completely with water and then sticking your finger in it causing the water to overflow the edge of the glass, only here the incompressible water is being pushed into the "Hydra" gun's hydraulic system.

The hydropump had looked like a conventional hand pump, albeit one with an overlapping and vented tubular handle that fits over the inner body of the pump, but that was somewhat misleading as to what lay inside. The condition of the pump inner bore is thus not critical, but the pump rod needs to be without any flaws to make the pump work properly. A similar water displacement pump is used in the "Black Sea" gun, but it uses a simple lever system to work the thin inner pumping rod back and forth which provides some mechanical advantage to the operator, while the "Hydra" requires that you directly push on the end of the rod. The tubular handle that telescopes over the inner pump body is there to prevent you from bending that thin rod which fastens into the rear of the handle, the numerous ports in the handle allowing any water to escape from the interior of the handle as otherwise it too would become a pump.
 

Bob Mallasch

New Member
Feb 14, 2016
4
5
3
85
New Zealand
The Italian Alcedo "Hydra" was the first hydraulic valve operation hydropneumatic speargun. It probably inspired a number of other hydropneumatic guns, but most of those used a sear tooth to directly hold onto the spear shaft rather than the patented hydraulic valve system in the "Hydra" which utilizes a "hydraulic locking chamber" to control water flow inside the gun, so these other hydropneumatic guns are not much different in operation to a standard pneumatic gun. You push the spear into the gun and the mechanism clicks as the sear tooth engages the spear shaft tail, there being no sliding piston inside the inner barrel of a hydropneumatic speargun. Some simpler construction guns engaged the spear shaft at the muzzle end, being forward latching spearguns, the shaft carrying a notch at the front end just behind the speartip, which weakens the spear.

Some years ago I pulled a long non-operational "Hydra" speargun apart to see what was inside and to discover how it worked, you can read the results here along with the many detail photos of the gun's innards. http://aquatech1.narod.ru/eng17.html

The accompanying article is a compilation of an original 1964 review of the "Hydra" gun and e-mail conversations with Sergiy Kravchenko, but some of it has been edited out, so the question has to be implied from the answer in some cases where the question is missing. The reason for the article being placed on the Aquatech web-site is that the "Hydra" speargun's operating principles were the direct inspiration for the subsequent "Black Sea" speargun developmental work (the "Black Sea" name came much later), although the layout is very different in the latter to produce a much more compact weapon for underwater hunting. The "Hydra" speargun's rubber bladder (located inside the blue anodized bulbous rear alloy tank) is an odd arrangement by today's standards, but it's use fitted in with the general appearance of the big carbon dioxide guns of the time (early to late sixties). It is interesting to note that if you reconfigure the heavy vented metal grille that separates the air filled and hence pressurized rubber bladder from the forward flooded sections of the gun by turning the grille into a pierced wall metal tube and wrapping the bladder around this tube in the form of a rubber hose you obtain the system used in the "RPS-3" hydropneumatic speargun. This space saving arrangement means that the pressurized air reservoir can now sit around the inner barrel instead of sitting directly behind it, but if you have the air reservoir forward of the gun's grip handle then you cannot use a hydraulic locking chamber design because water flows directly onto the spear shaft through the many holes in what is now the inner barrel of the gun. So the gun needs a mechanical sear tooth mechanism and a seal at the muzzle around the spear shaft to keep pressurized water inside the inner barrel, a very unlikely arrangement, or the rubber hose covered vented metal tube has to be restricted to a rear tank behind the gun's trigger mechanism (such hydropneumatic guns have been made, but they will not be discussed here).

Later hydropneumatic guns, such as the "Aquatech" and "Zelinka" models, replaced the rubber bladder/rubber hose flexible partition on the air reservoir with an annular piston sliding on the exterior of the inner barrel tube instead, but the "Aquatech" guns retained the "hydraulic locking chamber", although it was a much more compact arrangement than the large skyrocket shaped valve used in the "Hydra". Note that the bore of the hydraulic locking chamber must always be greater than the bore of the inner barrel or the system will not work, the lowest pressure has to be to the rear for the trigger or releasing valve to open rearwards and unplug the inner barrel once the rear section of the chamber is depressurized by opening the gun's trigger control valve.

As for the "Hydra" push-pull rear mounted hydropump, this is how it works. The hydropump's inner pump rod carries a cup type rubber seal, not unlike the one on the spear tail, that pushes water on the pumping stroke and temporarily collapses in on itself on the return stroke, thus allowing the pumping barrel to suck in water past the rubber cup seal for the next pumping stroke when the cup seal will flare outwards to again seal tightly on the pump's inner bore. The spear can be pumped in the front barrel in exactly the same way, but there the bore of the "pump" is larger, so more effort is required. A non-return valve, on this particular gun a thick rubber flap, seals the hydropump's small outlet hole inside the gun's flooded centre section thus preventing the building water pressure inside the gun escaping by pushing the pump handle backwards. Just as well, because the hydropump pump handle would hit you in the face otherwise!

There is a later version of the "Hydra" with some plastic parts and a more elongated appearance with respect to the rear tank which seems to be an even bigger gun than the original, but I have never located one in order to dismantle it. Collectors usually don't want to risk damage to their guns, but of all the speargun types you really need to open up hydropneumatic guns as saltwater can do nasty things inside the gun if you don't clean them out.

The "Hydra" shown here looks like it was washed out, but the original owner never flushed out the hydraulic locking chamber or the hydropump, the two most critical areas inside the gun and so it finally seized up. Aluminium oxide and fine sand particles spilled out of the hydraulic locking chamber once it was freed, but the hydropump is well and truly seized, so the gun is out of action. I suspect that the thick rubber bladder would split if recharged with pressurized air today, rubber product's lose their strength over time and any spare parts like a rubber bladder would be non-existent after all these years.
 

Bob Mallasch

New Member
Feb 14, 2016
4
5
3
85
New Zealand
Hi, I have just joined the forum and was pleasantly surprised to read the article on the Alcedo hydropneumatic spear gun.
I purchased one here in New Zealand the year they were available and have had many years of use with it entering ( and sometimes winning competitions ) just because of the power and reliability of the gun. Shooting and landing kingfish ( yellow tail ) over 50 pound in weight was not a problem.
The gun is still in perfect condition and I also have a spare new bladder and barrel. My grandson is now getting interested in spearfishing
and I hope he will progress to the point where he will be able to make use of it.
I am looking forward to browsing the columns ....Kind Regards Bob
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,952
571
153
Australia
Well it is great to finally hear from someone who actually used one of these guns. Up until now the only feedback I have ever received was from speargun collectors who seemed to be more interested in the “Hydra” as some sort of trophy, the guns being uncommon even when they were new (in the sixties) and were apparently very expensive to purchase. The then Australian distributor for the Alcedo “Hydra” told me that he only sold the “normal” model without the hydropump, in fact he was surprised to see the ruined “compressor” example I showed him which had the seized hydropump, so I failed to learn anything about the construction of the pump from him.

Bob can you tell us what it was like to swim with the “Hydra” gun as they are heavy and bulky compared to modern underwater weapons. Also how long did it take you to load it for each shot as to drive the shooting pressure up to the highest levels the user has to either pump the spear in the barrel (three strokes maximum) or work the hydropump (50 strokes maximum) or some combination of both.

A single spear stroke in the barrel is equivalent to 10 strokes of the hydropump, hence 50 strokes of the hydropump is equivalent to pumping the spear in the barrel five times. However five spear strokes is unrealistic as the spear can be pumped in the barrel twice while the operator is still floating in the water, but the instructions for the gun state that any third spear stroke will require some external support such as bracing one’s feet on the bottom. After that the hydropump is required as resistance to the spear being pushed into the barrel then becomes too great for a fourth stroke. Of course the start pressure in the air reservoir has a bearing on this pumping activity as the higher the start pressure then the sooner the operator has to switch over to using the hydropump. If the final shooting pressure is to be elevated to 100 atmospheres then the “Hydra” requires its internal air reservoir volume to be reduced using water injection to about one fifth of what it was originally at 20 atmospheres, the start pressure being quoted at 20 to 22 atmospheres for the early “Hydra” and “Hydra II” models. In the later “Sprint 62” model of the “Hydra”, the blue cylindrical bodied gun with the black plastic mid-handle, the “compressor” version of that gun had a start pressure of 40 atmospheres which meant that the gun could reach 100 atmospheres with only 25 strokes of the hydropump, but then all gun cocking required the use of the hydropump.
 

Bob Mallasch

New Member
Feb 14, 2016
4
5
3
85
New Zealand
Well it is great to finally hear from someone who actually used one of these guns. Up until now the only feedback I have ever received was from speargun collectors who seemed to be more interested in the “Hydra” as some sort of trophy, the guns being uncommon even when they were new (in the sixties) and were apparently very expensive to purchase. The then Australian distributor for the Alcedo “Hydra” told me that he only sold the “normal” model without the hydropump, in fact he was surprised to see the ruined “compressor” example I showed him which had the seized hydropump, so I failed to learn anything about the construction of the pump from him.

Bob can you tell us what it was like to swim with the “Hydra” gun as they are heavy and bulky compared to modern underwater weapons. Also how long did it take you to load it for each shot as to drive the shooting pressure up to the highest levels the user has to either pump the spear in the barrel (three strokes maximum) or work the hydropump (50 strokes maximum) or some combination of both.

A single spear stroke in the barrel is equivalent to 10 strokes of the hydropump, hence 50 strokes of the hydropump is equivalent to pumping the spear in the barrel five times. However five spear strokes is unrealistic as the spear can be pumped in the barrel twice while the operator is still floating in the water, but the instructions for the gun state that any third spear stroke will require some external support such as bracing one’s feet on the bottom. After that the hydropump is required as resistance to the spear being pushed into the barrel then becomes too great for a fourth stroke. Of course the start pressure in the air reservoir has a bearing on this pumping activity as the higher the start pressure then the sooner the operator has to switch over to using the hydropump. If the final shooting pressure is to be elevated to 100 atmospheres then the “Hydra” requires its internal air reservoir volume to be reduced using water injection to about one fifth of what it was originally at 20 atmospheres, the start pressure being quoted at 20 to 22 atmospheres for the early “Hydra” and “Hydra II” models. In the later “Sprint 62” model of the “Hydra”, the blue cylindrical bodied gun with the black plastic mid-handle, the “compressor” version of that gun had a start pressure of 40 atmospheres which meant that the gun could reach 100 atmospheres with only 25 strokes of the hydropump, but then all gun cocking required the use of the hydropump.
Hi Popggun, sorry for the delay but I had to go out of town to attend a funeral of the last diving buddy I was involved with.
About the Alcedo, I have the booklet that came with it and also correspondence from L'Alcedo in Turin dated 24th Aug. 1961 informing me of how to go about getting parts for the gun.
It was early days of spearfishing and we were buying the trigger mechanisms and making our own guns with up 4 double rubbers which resulted in a few skinned knuckles so when I saw the Alcedo I knew it was right for me.
Mine does not have the hydropump and the anodising has faded somewhat however as I have always dismantled, washed out and lubricated the gun after each expedition so it is in good working order.
As for weight etc. well obviously it is more cumbersome than than the conventional guns and I could not throw it a heap with all the others but it had the advantage that I didn't have to unload the gun when I came out of the water, just remove the spear, in fact at the start if we going out to the deep water looking for king fish I would preload the gun to the max. on shore, remove the spear and barrel
until we arrived at the dive site then replace the barrel, enter the water insert the spear and I was good to go and could get the first of the kingfish coming up for a look. We were diving at Whitianga (bay of islands) a lot where quite often the the deep sea angler boats would come by with their rods out looking for shark and marlin.
Being able to shift the lower bezel on the barrel was a good function to allow you to cut the power by half and also release the water in the barrel.
From memory I could load the gun nearly 4 strokes in deep water, but if I saw rock at the right depth I would be able to put my full body weight on it and get another stroke.
I had spare spears made of hi tensile steel with the head and floppers welded directly onto the shaft, the shaft was tapered down to the seal which I had had made. The spear was copper then chrome plated however I never lost or bent one.
The method I used when I had shot a fish was to hook the gun onto my lead belt which then gave me both hands free.
After bringing the fish to me I would put put my left hand between the gill area then push the spear right through, reverse it and push it back through the same hole, then take the fish back to the float and push it all away from me as this was shark territory and there was always blood in the water during this operation.
Anyway i had better stop rambling on....Regards Bob
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,952
571
153
Australia
Flexible membrane guns which use a rubber bladder or tube as an internal moving bulkhead tend to lose air pressure through the wall of the rubber due to its inherent permeability to gases. Thus over time any “Hydra” would experience a fall in start pressure even though there were no air leaks from the gun in the usual sense, hence a “Hydra” would gradually become easier to load as the pressure inside the rubber bladder fell away. To top this internal air pressure up from time to time a hand pump with manometer (pressure gauge) was supplied, it can be seen in the parts diagram, but this air pump is often missing from surviving guns. Other hydropneumatic guns such as the much later Russian “RPS-3” (seventies) and “Kobra” (contemporary) also gradually lose pressure through the rubber tubes which surround their multiple port drilled aluminium alloy inner barrels, hence the guns require more frequent pumping with their hand pumps, but the guns are usually depressurized when stored for any length of time for reasons which will soon be discussed.

As Bob says the “Hydra” is one of the few guns that can be charged to shoot and then the spear pulled out and the front barrel unscrewed leaving water under pressure inside the gun. The problem of getting the spear back into the gun after the barrel is re-installed is circumvented by the sliding annular collar at the base of the front barrel which when moved forwards exposes a ring of small ports. These ports allow the spear to be pushed down the barrel with next to no effort as water behind the spear tail’s rear seal is diverted from entering the gun and instead escapes via the ports back to the surrounding environment. The ring of ports also act as a power reducer during the shot by providing an alternate pathway for water under pressure to exit the gun rather than it all being directed to pushing the spear out of the barrel. On a modern hydropneumatic, compressor equipped “Black Sea” gun the spear can also be pulled out of a fully charged to shoot gun, but there is no way of then pushing the spear back into the barrel as there is no bypass option for water being driven rearwards by the spear tail to exit the gun, unless the hydraulic locking chamber is open which means discharging the gun with a “dummy shot” first. The hydraulic locking chamber hydropneumatic guns can all function as giant water pistols with their spear removed, however the water column blasted out of the gun is very dangerous if the guns are at full power and should never be pointed at any one while pulling the trigger on land.

I suspect that some gun owners followed the instructions to store the “Hydra” filled with water which was slightly under pressure. This was made possible by using a partial spear stroke to get the firing valve to shut under pressure so that it acted as a non-return valve to keep all water inside the gun and then the spear and barrel were removed. The idea behind this water filled storage method was to remove the effect of the rubber bladder being continually pressed by the high air pressure acting inside it against the multiple holes in the vented bulkhead which separated it from the rest of the gun’s interior. Water trapped under pressure would then balance the forces acting on either side of the rubber bladder and thus avoid the situation where pressurised air on one side was trying to extrude the rubber bladder through the many small vent holes in the bulkhead with only atmospheric pressure acting on the other side. This was OK provided the gun was filled with freshwater, plus it made flooding of the gun easier as the guns need to be completely flooded to function properly during a spearfishing session, but if saltwater was left inside the gun then over time the effects would be disastrous as corrosion set in. Possibly the official instructions were not always heeded and an intended water change over was deferred and then eventually forgotten about. Alternately the air pressure could be released from the rubber bladder and in my view that was the best option if you wanted to remove stress from the rubber bladder, but that required a future pumping session with the hand pump.

The later “Hydra Sprint 62” had a relatively small air reservoir which enabled it to be pumped up to its start air pressure of 40 atmospheres more rapidly and provided an internal volume which could be changed significantly as water was progressively injected into the gun, otherwise the overall compression ratio of 2.5 would not have been possible with only twenty five hydropump strokes going into the gun. The actual compression ratio for this model with a single spear stroke was about 1.4, the gun’s start pressure being reduced from 40 atmospheres to 20 atmospheres in the “normal” version of the “Hydra Sprint 62” (no hydropump/compressor was fitted) for muzzle-only loading, but this compression ratio increased with subsequent spear strokes as the reservoir volume was decreasing while the barrel volume being pushed into the gun was staying the same for each stroke.
 
Last edited:

Bob Mallasch

New Member
Feb 14, 2016
4
5
3
85
New Zealand
Flexible membrane guns which use a rubber bladder or tube as an internal moving bulkhead tend to lose air pressure through the wall of the rubber due to its inherent permeability to gases. Thus over time any “Hydra” would experience a fall in start pressure even though there were no air leaks from the gun in the usual sense, hence a “Hydra” would gradually become easier to load as the pressure inside the rubber bladder fell away. To top this internal air pressure up from time to time a hand pump with manometer (pressure gauge) was supplied, it can be seen in the parts diagram, but this air pump is often missing from surviving guns. Other hydropneumatic guns such as the much later Russian “RPS-3” (seventies) and “Kobra” (contemporary) also gradually lose pressure through the rubber tubes which surround their multiple port drilled aluminium alloy inner barrels, hence the guns require more frequent pumping with their hand pumps, but the guns are usually depressurized when stored for any length of time for reasons which will soon be discussed.

As Bob says the “Hydra” is one of the few guns that can be charged to shoot and then the spear pulled out and the front barrel unscrewed leaving water under pressure inside the gun. The problem of getting the spear back into the gun after the barrel is re-installed is circumvented by the sliding annular collar at the base of the front barrel which when moved forwards exposes a ring of small ports. These ports allow the spear to be pushed down the barrel with next to no effort as water behind the spear tail’s rear seal is diverted from entering the gun and instead escapes via the ports back to the surrounding environment. The ring of ports also act as a power reducer during the shot by providing an alternate pathway for water under pressure to exit the gun rather than it all being directed to pushing the spear out of the barrel. On a modern hydropneumatic, compressor equipped “Black Sea” gun the spear can also be pulled out of a fully charged to shoot gun, but there is no way of then pushing the spear back into the barrel as there is no bypass option for water being driven rearwards by the spear tail to exit the gun, unless the hydraulic locking chamber is open which means discharging the gun with a “dummy shot” first. The hydraulic locking chamber hydropneumatic guns can all function as giant water pistols with their spear removed, however the water column blasted out of the gun is very dangerous if the guns are at full power and should never be pointed at any one while pulling the trigger on land.

I suspect that some gun owners followed the instructions to store the “Hydra” filled with water which was slightly under pressure. This was made possible by using a partial spear stroke to get the firing valve to shut under pressure so that it acted as a non-return valve to keep all water inside the gun and then the spear and barrel were removed. The idea behind this water filled storage method was to remove the effect of the rubber bladder being continually pressed by the high air pressure acting inside it against the multiple holes in the vented bulkhead which separated it from the rest of the gun’s interior. Water trapped under pressure would then balance the forces acting on either side of the rubber bladder and thus avoid the situation where pressurised air on one side was trying to extrude the rubber bladder through the many small vent holes in the bulkhead with only atmospheric pressure acting on the other side. This was OK provided the gun was filled with freshwater, plus it made flooding of the gun easier as the guns need to be completely flooded to function properly during a spearfishing session, but if saltwater was left inside the gun then over time the effects would be disastrous as corrosion set in. Possibly the official instructions were not always heeded and an intended water change over was deferred and then eventually forgotten about. Alternately the air pressure could be released from the rubber bladder and in my view that was the best option if you wanted to remove stress from the rubber bladder, but that required a future pumping session with the hand pump.

The “Hydra” had a relatively small air reservoir which enabled it to be pumped up to its start air pressure more rapidly and provided an internal volume which could be changed significantly as water was progressively injected into the gun, otherwise the overall compression ratio of 5.0 would not have been possible with five spear strokes or their equivalent in hydropump strokes going into the gun. The actual compression ratio with a single spear stroke was about 1.4, but this increased with subsequent spear strokes as the reservoir volume was decreasing while the barrel volume being pushed into the gun was staying the same for each stroke.

When I dismantled the gun for cleaning I would periodically deflate the bladder for a thorough clean out and refill by decanting from a regulated small pressure cylinder and gauge .( naughty if you were competing)
I thought the trigger mechanism was well thought out to release the spear and the fact they had a hole from the main pressure chamber
to the back area where the bladder valve was so that the valve did not have to contend with any more than the 320 psi it was filled to.
I made a 1/2 inch perspex underwater movie camera housing which was attached to the gun. It was positioned so the film showed the spear head in the top right hand of the frame. The camera was a Eumig 8mm with hand rewind and would leak at a depth of 30 feet or so but I got some really interesting movies especially when I spent a couple of weeks diving around New Calendonia
 
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popgun pete

popgun pete

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Jul 30, 2008
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Australia
Alcedo Hydra Sprint an.gif

Here is a diagram for the “Hydra Sprint 62” showing how the gun is assembled, the external tank tube providing the structural member that holds all the gun’s components together. A group of cylindrical sub-sections are slid into the tank tube and held in place by two large internal circlips positioned at either end of the tank tube. A number of metal screws pass through the tank wall to help secure the front and rear internal sections of the gun, the front screws also attaching the plastic pistol grip handle under the tank. Note that wherever the tank tube is penetrated by an opening a pair of “O” rings on either side of the breach isolate that position so that internal pressure cannot escape nor ambient water leak into the gun’s interior, but a film of water can get into the tiny annular gaps between the inner wall of the tank and the exposed part of the inner component. For this reason the guns need to be thoroughly washed in order to avoid any corrosion or deposits that would make disassembly difficult at some future date where close-fitting cylindrical sections have to be slid out of the tank tube which thus needs to retain a smooth inner bore right along its entire length. A soft-faced hammer is depicted in the maintenance instructions, but this is being used to dislodge tight seals that have stuck in place rather than battling the jamming effects of corrosion. Unfortunately aluminium oxide forms a fine white powder which expands and removes any clearances and then one needs either a larger hammer or a hydraulic press which may destroy the gun if used without some caution and a certain degree of luck as success is not always guaranteed even if the dismantler knows exactly what he is doing.

Note that in the original “Hydra” air pressure is contained in a rubber bladder which water in a bulbous metal tank surrounds when water is injected into the gun, but this arrangement is reversed in the “Hydra Sprint 62” where the air pressure is now inside the rear tank which surrounds the rubber bladder or pipe that contains the injected water. A multi-hole, perforated metal tube inside this rubber pipe prevents the pipe from collapsing under pressure when the gun’s interior is not filled with water. Earlier in this thread I stated that such guns were not going to be discussed here, but at that time I did not know about the internal layout of the “Hydra Sprint 62” gun which I had only ever seen in photographs. A forum member sent me the instructions for these guns and then all was made clear.

Twenty five strokes of the hydropump inject enough water to remove 60% of the air reservoir volume leaving only 40% remaining which means that a start pressure of 40 atmospheres will be elevated to 100 atmospheres for shooting. In the instructions it states that if the reservoir start pressure is reduced to 20 atmospheres, then to achieve 100 atmospheres the hydropump will require approximately double the number of strokes, but this is incorrect. Another twenty five strokes of the hydropump, i.e. fifty strokes in total, will remove another 60%, yet there being only 40% remaining this is impossible. Actually with the gun at 20 atmospheres start pressure, which is the pressure level also used in the “normal” version of the same gun, it will only require a total of 33 strokes of the hydropump.

The reasoning is as follows:-

The hydropump moves an incompressible column of water with each pump stroke, hence if 25 strokes account for 60% of reservoir volume then each stroke equates to 2.4% of that volume. In order to boost 20 atmospheres to 100 atmospheres that requires the reservoir volume to be reduced by 80% and 80/2.4 equals 33.3 pump strokes. Three spear strokes in the barrel of the “normal” version of this later gun will push the 20 atmospheres start pressure to 70 atmospheres which means that only 28.6% of reservoir volume remains and 71.4% has been removed by water injection. Using the figure of 2.4% per hydropump stroke then that 71.4% of reservoir capacity represents 29.75 hydropump strokes, close enough to 30 which indicates that the 10 hydropump strokes equivalence to a spear stroke is maintained in this gun. Unlike its more bulky predecessor it will not swallow 5 spear strokes due to its smaller air reservoir capacity as the gun is designed for 40 atmospheres operation and the use of the compressor rather than the latter being an afterthought despite the option of leaving it off the “normal” version of the later gun. The “Hydra II” hydropump moves 1.56% of reservoir volume per stroke (50 strokes x 1.56% equals 78% which leaves 22% and boosts the 22 atmospheres start pressure to 100 atmospheres), thus if the barrel and hydropump swept volumes are the same in all the versions of the “Hydra” guns then the “Hydra Sprint 62” has a reservoir volume of 65% of that of the “Hydra II”.

A series of 9 disc-shaped floats on the front barrel tube and a counterweight plug in the rear cap indicate a rather heavy gun despite the slimmer proportions of this later model compared with the somewhat bulbous form of the original “Hydra” and “Hydra II”. The “Hydra” is a unique gun which uses the accumulator principle of its hydraulic operation to create a high pressure, high compression ratio gun which would normally be impossible to cock by muzzle loading if you wanted to use 40 atmospheres start pressure in a pneumatic speargun, however the gun also shoots a long column of water behind the spear that detracts from its efficiency even though that may be of little concern given the number of shots put through the gun on any particular outing.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,952
571
153
Australia
Another account of an "Alcedo in action" is discussed here:

http://tombyronchronicleofscubadivinginaustralia.info/1917 TO 1959.html

The relevant section is excerpted here:
Theo had been knocked sideways. The shark had bitten a piece from the leg of his rubber suit and left four teeth marks in it and had then disappeared with his Alcedo compressed air gun. It seems that as Theo sat patrolling the deep water in front of him with his spotlight, the shark (unidentified) sneaked around the light and attacked from the side. Sixth sense made Theo look around, just in time to see the huge fish right on him. In the same movement, he swung his gun around and fired. The next thing he knew he was on his back with water seeping through his underwear. Where the spear went he did not know. Theo left the water three quarters of an hour later because, again, his suit was full of water. Early next morning Bev Marshall found Theo's gun some distance away, with the barrel bent at about thirty degrees. The spear, which lay nearby had the head snapped off and bent at approximately 60 degrees, it was obvious that he had scored a hit.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,952
571
153
Australia
Another "hydropumper" gun is this one: http://fishgun.spb.ru/index.php?page_id=samopal&item=g_pnevma3
Unlike the Aquatech it has a mechanical trigger mechanism and is not valve operated as they are. The hydropump is fitted into the grip handle, but operates in the same way in that it is a water displacement pump as a metal rod pushes in though a stationary rubber seal and the volume it occupies then drives water out of the bore of the hydropump and into the gun. Note that this gun can only be charged with the hydropump and that the spear has no tail seal, relying instead on the spear being a very close fit the barrel's bore diameter. Any grit inside the barrel and then there will be problems!
hydropump gun.jpg
 

DIM

Active Member
Jul 17, 2012
10
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sascatoon
thanks for my website link. if it is interesting I showe some test video. but not in Ukrania. On Cyprus.
it is absolutly not like aquateh. It havw movement burrel and after shot burrel automaticly closed main valve. Like as the ship's gun almost :)