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Thread Status: Hello
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The rear housing construction ideally lends itself to that rocking bar system as the necessary internal rail is there to both pivot from and trap the rocking bar in the horizontal position where the trigger cannot push it up any further at its rear end no matter how hard you pull on the trigger (within sensible limits of course). Milling the rear housing would have been expensive, so the more complicated the parts were that went inside it then the more justification for doing it that way. When I showed a machinist the rear housing and said how would you go about making this, he replied "don't even think about it"! That is why I bought the second gun when I saw the rear housing on the first gun was cracked (thanks to someone forcefully screwing it up and over the terrible quality rubber rear seal).
Here is a modified diagram showing the production speargun's extended centre section which added an air release screw on the LHS. This redesign also added the externally threaded alloy nuts whose purpose is to squeeze flat washer type rubber rings so that they expand radially inwards and outwards and seal the inner barrel at the front and rear air reservoir bulkheads. The rubber rings used in this location are of good quality, unlike everywhere else, but the very fine threads on the nuts limit the degree to which they can be tightened up and create the best possible seal. The front alloy nut is longer (5 threads) and inside the air reservoir, while the rear nut is shorter (only 3 threads!) and located outside the air reservoir. So an external rubber seal holds air pressure in the gun at the back end of the air reservoir! This is possible because only a tiny ring of rubber cross-sectional area is directly exposed to the compressed air pressure, otherwise those 3 metal threads on the rear nut could be stripped. If an "O" ring is substituted here then you need another "O" ring placed on the other side of that bulkhead as that pressure exposed area will become larger as an "O" ring leaves a bigger gap due to its circular cross-section rather than the squared corners of a rubber washer.
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Everything and more is in this thread, the user manual does not say much except for telling the user what not to do! Read the thread and then let me know what you think may be missing, or need to know.
Here is the hand pump that straps over the gun's mid-section. The small washer on the nose of the pump presses against the outer body of the mid-section to seal. The two seals on the pump piston use the same rubber ring as the muzzle seal and are separated by one of the plastic rings also used in the muzzle. The air inlet valve is a strip of rubber that can be taken out and installed in a new position if it has punctured, keeping the damaged area and the join away from the small air inlet hole at the bottom of one of the four holes in a ring around the mid-section. If the rubber strip has softened then it will probably break through again with the compressed air pressure trying to force it through the hole, I had that happen and had to make a new rubber strip. The size of the rubber strip is given in post #54, item 3.
The parts diagram can be seen here http://www.spearboard.com/showthread.php?p=1868448 as I had no attachment capacity left to show it here. Sourced from the 1990 edition of the user manual, it contains a few drafting mistakes which I corrected in my own version showing the annular nuts that seal off the inner barrel tube, but I did not show the hand pump on that diagram.
The parts diagram can be seen here http://www.spearboard.com/showthread.php?p=1868448 as I had no attachment capacity left to show it here. Sourced from the 1990 edition of the user manual, it contains a few drafting mistakes which I corrected in my own version showing the annular nuts that seal off the inner barrel tube, but I did not show the hand pump on that diagram.
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The recent reference to the "RPS-3" User Manual made me realize that one aspect that has been neglected so far in this thread is the gun's specifications or technical characteristics, as stated in the User Manual. So here they are for the short production gun with the 40 cm length inner barrel, not the longer prototype with the 70 cm length inner barrel. On-line references sometimes blur the distinction as to which of these guns is being discussed.
Technical Characteristics
Range shooting underwater with chamber pressure 6.2 - 6.5 MPa, not less than 4 metres
Effort when charging adjustable from range 200 to 400 Newton (20.4 to 40.8 kg)
Length of gun with spear: 85 cm
Weight of gun with spear, not more than 1.3 kg.
Note that 10 bar is equal to 1.0 MPa (Mega Pascal), so that is 62 - 65 bar (63.2 - 66.3 kg/cm2) of chamber pressure! No surprise then that the "RPS-3" speargun was supplied with a long and narrow bore hand pump. According to the User Manual it takes from 100 to 140 pump strokes to achieve a pressure level from 4 to 6.5 MPa to shoot as far as 4 metres and thanks to the friction of the tight pump seals (they are neither "O" rings nor cup type seals) they soon heat up the body tube of the pump. There is no actual pump table given. The pump seals do improve with extended use, but with too much lubrication they swell and jam inside the pump bore, requiring the pump to be disassembled to free them by unscrewing the special bolt that is the seal carrier from the inner end of the pump rod. I have had to do that a number of times. (I once purchased a spare pump where a hacksaw had been used in desperation on the pump body to free the pump piston by some ignorant owner, I only purchased it to obtain the pump rod which is also a spare spear shaft, luckily that had not been cut in half.) Remember that the folding pump "handle" is actually a foot rest with the gun and pump body clamped together at a right angle and the combined assembly reciprocating up and down on the stationary pump rod when you work the pump. So both hands are on the gun body using it as a giant T-handle and you use your body weight to force it down at increasing levels of resistance. A pressure of 65 bar is equal to 943 psi! A carbon dioxide gun only produces 900 psi.
The User Manual states in the "Rules or Principles of Use" section that (the user) "ought to consider that when stated pressure (is used) in chamber (then) for load in barrel spear with loader (it is) necessary to apply effort not less than 380 Newton". That is 38.7 kgf to get the spear started moving in the inner barrel! So if users do not wish to turn themselves inside out loading their gun for each shot then it is stated in the following sentence that they can use the gun at lower pressures with correspondingly lower performance and my guess is the practical shooting range would then be about 2 metres or 6.5 feet, particularly if you wanted to minimize the chances of cracking the plastic rear handle by reducing the effort applied to it during muzzle loading against your thigh.
The production "RPS-3" gun has been subsequently tested and found to have an efficiency of 35%, which is relatively low for a pneumatically powered speargun, hence a big loading effort does not result in a high level of shooting performance. A quiet and accurate shot was probably its main attraction (no fast moving piston and rival domestic spearguns were then of poor quality), I note that some "RPS-3" guns have subsequently been fitted with lights for night hunting in rivers and lakes.
Technical Characteristics
Range shooting underwater with chamber pressure 6.2 - 6.5 MPa, not less than 4 metres
Effort when charging adjustable from range 200 to 400 Newton (20.4 to 40.8 kg)
Length of gun with spear: 85 cm
Weight of gun with spear, not more than 1.3 kg.
Note that 10 bar is equal to 1.0 MPa (Mega Pascal), so that is 62 - 65 bar (63.2 - 66.3 kg/cm2) of chamber pressure! No surprise then that the "RPS-3" speargun was supplied with a long and narrow bore hand pump. According to the User Manual it takes from 100 to 140 pump strokes to achieve a pressure level from 4 to 6.5 MPa to shoot as far as 4 metres and thanks to the friction of the tight pump seals (they are neither "O" rings nor cup type seals) they soon heat up the body tube of the pump. There is no actual pump table given. The pump seals do improve with extended use, but with too much lubrication they swell and jam inside the pump bore, requiring the pump to be disassembled to free them by unscrewing the special bolt that is the seal carrier from the inner end of the pump rod. I have had to do that a number of times. (I once purchased a spare pump where a hacksaw had been used in desperation on the pump body to free the pump piston by some ignorant owner, I only purchased it to obtain the pump rod which is also a spare spear shaft, luckily that had not been cut in half.) Remember that the folding pump "handle" is actually a foot rest with the gun and pump body clamped together at a right angle and the combined assembly reciprocating up and down on the stationary pump rod when you work the pump. So both hands are on the gun body using it as a giant T-handle and you use your body weight to force it down at increasing levels of resistance. A pressure of 65 bar is equal to 943 psi! A carbon dioxide gun only produces 900 psi.
The User Manual states in the "Rules or Principles of Use" section that (the user) "ought to consider that when stated pressure (is used) in chamber (then) for load in barrel spear with loader (it is) necessary to apply effort not less than 380 Newton". That is 38.7 kgf to get the spear started moving in the inner barrel! So if users do not wish to turn themselves inside out loading their gun for each shot then it is stated in the following sentence that they can use the gun at lower pressures with correspondingly lower performance and my guess is the practical shooting range would then be about 2 metres or 6.5 feet, particularly if you wanted to minimize the chances of cracking the plastic rear handle by reducing the effort applied to it during muzzle loading against your thigh.
The production "RPS-3" gun has been subsequently tested and found to have an efficiency of 35%, which is relatively low for a pneumatically powered speargun, hence a big loading effort does not result in a high level of shooting performance. A quiet and accurate shot was probably its main attraction (no fast moving piston and rival domestic spearguns were then of poor quality), I note that some "RPS-3" guns have subsequently been fitted with lights for night hunting in rivers and lakes.
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I recently discovered that this later version of the Alcedo "Hydra" has a rubber pipe surrounding a multi-ported metal tube in the compressed air reservoir in the rear end of the gun. I had thought this idea was originally presented in the "RPS-3", but I think this Italian gun precedes it, except that here the spear does not travel inside the ventilated tube. That means the spear does not experience the variable throttle effect as it passes by successive rows of ports in the tube, something which the "RPS-3" speargun had to contend with and thus decreased its efficiency, particularly in the shorter production version of the gun.
You can see a photo of this gun here, it is at the top of the listing: http://www.apneateam.it/Fucili Storici/Fucili Storici - Willy the Kidd.htm
You can see a photo of this gun here, it is at the top of the listing: http://www.apneateam.it/Fucili Storici/Fucili Storici - Willy the Kidd.htm
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The RPS-3 gun was supplied in a nice brown vinyl carry case that had a shoulder strap with metal buckles and attachment fittings and contained an internal sub-section or pocket for the hand pump to slide neatly into. The bags were longer than the guns were as the gun was carried with the spear already inserted in the barrel, but without any water inside the gun it was not cocked as such. Not such a good idea if the air reservoir leaked and gradually pressurized the inner barrel! The carry case looked more like something a firearm would be carried in rather than a speargun. I had three of these bags, but I never used them. I say "had" because I have just found out that they were stolen in a burglary about this time last year and it was only because the subject came up recently that I remembered not seeing them for a very long time and went looking for them. Two of the bags have the gun's name heat stamped by the manufacturer on the press studded closure flap as "PПC-3" in large block characters, the other bag looked the same, but was of a heavier vinyl cloth backed material and unmarked as it was of earlier manufacture. If anyone sees such a bag then they will recognize them by that branding as they are unique to the gun.
The port spacing in the production "RPS-3" gun as measured.
Note that full water flow where the sum of the areas of 81 port holes matches the shaft cross-sectional area occurs at a distance of 14.5 cm from the rear edge of the inner barrel. Before that position is reached the spear has insufficient water coursing into the inner barrel behind it in order to drive it without some form of throttling taking place, hence the gun's efficiency is impaired by this flow restriction. The body of the shaft acts as a sliding throttle bar as when it is positioned under any given ring of ports then there is nowhere for water sourced from them to flow into. Water, which is incompressible, needs a gap to open up by the shaft vacating that position located directly beneath them.
Note that full water flow where the sum of the areas of 81 port holes matches the shaft cross-sectional area occurs at a distance of 14.5 cm from the rear edge of the inner barrel. Before that position is reached the spear has insufficient water coursing into the inner barrel behind it in order to drive it without some form of throttling taking place, hence the gun's efficiency is impaired by this flow restriction. The body of the shaft acts as a sliding throttle bar as when it is positioned under any given ring of ports then there is nowhere for water sourced from them to flow into. Water, which is incompressible, needs a gap to open up by the shaft vacating that position located directly beneath them.
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O
omega3
Guest
Buggers stole your bags...Mine is black, I will see if it has the stamp when I get home.
Looking forward to taking it in the water soon for posterity. I have often wondered if the rubber sleeve material could be improved. ie quality surgical tubing of a particular wall thickness as an alternative to the hard as rock supplied rubber tubing...and maybe more importantly getting a tube with as minimal as possible ID forced on....hmmmm
The other one (mid handled)is unfortunately knackered. when replacing the reservoir after cleaning, it (me) forced the molded handle along the shaft and the jam at the front is not strong enough to hold it. trying to figure out a solution whereby I can re bond the handle to the checkered machined grip on the barrel....without destroying it!! tempted to heat the barrel enough to soften/melt the plastic so it can be removed, re-bore, re-bond. its a tall/time consuming order...
Looking forward to taking it in the water soon for posterity. I have often wondered if the rubber sleeve material could be improved. ie quality surgical tubing of a particular wall thickness as an alternative to the hard as rock supplied rubber tubing...and maybe more importantly getting a tube with as minimal as possible ID forced on....hmmmm
The other one (mid handled)is unfortunately knackered. when replacing the reservoir after cleaning, it (me) forced the molded handle along the shaft and the jam at the front is not strong enough to hold it. trying to figure out a solution whereby I can re bond the handle to the checkered machined grip on the barrel....without destroying it!! tempted to heat the barrel enough to soften/melt the plastic so it can be removed, re-bore, re-bond. its a tall/time consuming order...
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I replaced the carry bag, another dark brown one, made of the same thin vinyl canvas (type) backed cloth, which if you pull too hard on the press studs they pull free of the vinyl, so you need to twist and ease them off. Owners have used floppier tubing, but its gas permeability is often greater, so the gun loses pressure more quickly, but it takes weeks if not months to do so. However my advice after using the gun is to depressurize it anyway and check the reservoir interior for water as I think they always leak a bit. This is because the hydro-static pressure as the gun charges with muzzle loading exceeds air pressure inside marginally and it also forces water in the front bulkhead end. Freshwater (lake or river) no problems, but saltwater is a disaster.
Hence after using the gun in saltwater screw the rear grip off, remove the front tank from the mid-section (let all the air out first) and then throw the 3 sections in a tub of clean water. Swish them around, dry everything off, lubricate it and keep the gun dismantled until the next time you want to use it.
Hence after using the gun in saltwater screw the rear grip off, remove the front tank from the mid-section (let all the air out first) and then throw the 3 sections in a tub of clean water. Swish them around, dry everything off, lubricate it and keep the gun dismantled until the next time you want to use it.
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O
omega3
Guest
If someone is after a copy of the manual...hassle me to remember and I will scan it and email(copyright etc??)
it has all the cutaways/plan drawings etc if I remember right. Saw it in the loft a month or so ago looking fairly poorly so I had
better scan it soonish
it has all the cutaways/plan drawings etc if I remember right. Saw it in the loft a month or so ago looking fairly poorly so I had
better scan it soonish
O
omega3
Guest
Yes, about as cheap utilitarian as is possible like the plastics and rubbers too
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O
omega3
Guest
I have access to some interesting tubings but what I would like to try is as low an ID as possible forced over the tube as opposed to the rigid ID of the tubeing matching the OD of the tubular..."floppier" ?... nah, tighter fit, already in compression.
By "floppier" I meant latex and other semi-translucent gum type rubber, rather than carbon black reinforced rubber which is what is used in vehicle components and sporting goods in the days when you could have any color that you wanted, as long as it was black! Some black tubing is woven fiber reinforced, but that stops the tube diameter expanding which would be totally useless in the RPS-3. In Russia guys are continually searching for sources of rubber tube as their "still operational" (note, this is a relative term) guns require a replacement when the original conks out. It puzzles me why someone does not set up a business molding new plastic handles (using thermoplastic of a modern formulation in a modern injection molding machine that can use that stuff), produce new rubber pipes with locking end clamps (to avoid using thin string winding on twenty or so turns to secure the ends) and all new rubber seals of the "O" ring format with only a few seals remaining as rectangular packings, such as the trigger pull rod and the muzzle nozzle seal. New inner alloy barrels drilled to provide 80 holes "earlier", as shown above, or stainless steel tubing which can be more heavily ported by increasing hole drilling density. The "only" problem with using stainless steel tubing is galvanic corrosion at where it will encounters the alloy bulkheads, but if the gun is regularly pulled apart then there should be no problem. Why the guns were not routinely pulled apart previously was the absurdly tight rubber seals, as burdened with untrimmed rubber flash at the molding part line they required "King Kong" to grab one end while "Godzilla" twisted the other. The supplied multi-tool was useless except for damaging the unyielding alloy bulkheads as they stubbornly refused to turn, but it was good for tightening the spear tails onto the spear shafts. There is a notional screwdriver blade at the tip, but only use it if you want to damage the slot in the air release screw set into the mid-body section. Lastly the RPS-3 hand pump needs some proper seals and a piston that will not chew up the pumping barrel bore as the metal end washers that clamp the existing "seals" move off-axis.
I finally did this drawing of water flow in rubber hose type hydropneumatic spearguns where the spear body prevents water inflow until it moves out from under any given ring of holes in the inner barrel tube. Once all the port holes are uncovered then all of them can contribute to the water flow that drives the spear from the gun.
The spear as seen here operates as a sliding column valve that throttles the shot in the early stages of the spear's propulsion out of the gun. When this rubber tube over a ventilated metal pipe pressure transfer system was used in the Alcedo "Hydra Sprint" such problems were not encountered as the spear sat in an inner barrel with the ventilated metal pipe section immediately behind it. In that embodiment the water was able to flow through every port hole in the ventilated metal pipe from the commencement of the shot, but it made for a much longer gun using the classic slim forward barrel, mid-handle section and rear tank layout.
Spear diameter of 9 mm has a cross-sectional area of 63.617251235 square millimeters
Inner barrel port of diameter 1.0 mm has a cross-sectional opening of 0.7853981634 square millimeters.
Multiply x 81 ports combined cross-section equals 63.617251235 square millimeters which is the same as the shaft cross-section.
The spear as seen here operates as a sliding column valve that throttles the shot in the early stages of the spear's propulsion out of the gun. When this rubber tube over a ventilated metal pipe pressure transfer system was used in the Alcedo "Hydra Sprint" such problems were not encountered as the spear sat in an inner barrel with the ventilated metal pipe section immediately behind it. In that embodiment the water was able to flow through every port hole in the ventilated metal pipe from the commencement of the shot, but it made for a much longer gun using the classic slim forward barrel, mid-handle section and rear tank layout.
Spear diameter of 9 mm has a cross-sectional area of 63.617251235 square millimeters
Inner barrel port of diameter 1.0 mm has a cross-sectional opening of 0.7853981634 square millimeters.
Multiply x 81 ports combined cross-section equals 63.617251235 square millimeters which is the same as the shaft cross-section.
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