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Hydro/pneumatic gun

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Another diagram where the ported section is shown enlarged and the flow restriction quantified as each ring of ports is effectively brought into action as the spear body vacates the space below each set. No opened up gap then no water flow due to the incompressibility of water. Note that 145 mm represents 36% of the inner barrel length of 400 mm.
 
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Here is the original layout used in the prototype RPS-3 speargun which had a 70 cm length inner barrel and alternating four port rings at 45 degrees rotation as they were drilled out along the barrel in a combined series of 41 rings; 21 "A" Rings and 20 "B" rings. If you were not a crazy man after drilling out a half dozen barrels then you had benefited from the decision not to drill out the entire barrel from one end to the other thus peppering it completely with ports!
 
As speargun designers pick up design cues from existing models and then create alternative solutions we find a progression of types and this is how I believe the "RPS-3" hydropneumatic speargun evolved. As far as I can tell all but the "HYDRA SPRINT 62" have appeared in the pages of the Russian dive magazine "Athlete-Submariner" (or "Underwater Sportsman").
 
Another source of information is the actual "RPS-3" Russian patent. Here we see the document header (note the 1974 application date) and the original patent diagram. Note also that the trigger mechanism as depicted is rather less ambitious than the version used in the production gun which would have significantly added to the cost with its many parts and auto-applied safety interlock reset. In my view the best part of the gun!
 
Wow you have some very detailed reading here. I am new to posting here and I have one of these guns as it was a package deal with some old russian air tanks and flippers that I needed (wanted).So should I even bother trying to operate this gun or just spend the money on a new one?Here in Canada we cannot hunt with them so testing it in a lake is risky to see if it works.I have a Rob Allen tuna gun for fishing in Cuba so maybe I can give this russian one to someone there.
 
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RPS-3 hydropneumatic spearguns are rare in good order as owners never realized the maintenance that was required to keep the gun functioning and corrosion set in making everything that much harder, especially if you left the spear in the gun!
 
My RPS-3 speargun was not latching properly and the gun did not screw up as far as before because the outlet air release screw was stopping at a different position. I tracked the reason that this was happening down to the combined width of the "O" ring and the flat rubber washer being slightly too thick. Remember that the original seal is two flat rubber washers, but when replacing one of them with an "O" Ring for improved gas sealing you have to maintain the same thickness as before hence I needed a slightly thinner flat washer so that their combined thickness equals what the two flat washers provided before.
 
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The front end is where water often penetrates into the air reservoir as hydrostatic pressure can push the seals inwards and cause a leak as the pressure being developed exceeds that in the reservoir during the time interval that a loading effort is being applied.
 
I note that the instruction manual for the RPS-3 was updated at some time as can be seen in this photo of a gun for sale. Some of the other photos are included as they show the RPS-3 from different angles.


 
And a few more of the rear handle and the muzzle, spear, etc.


Note that the actual pointed tip of the spear tip screws off and the guns also came supplied with a fatter simple tip with no floppers that can be seen here on the spear.
 
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Also note that the pile of spare parts shown in the above photos are muzzle rubber seals and the black plastic backing rings that sit directly behind them. You received 40 spare muzzle seals with each new gun as the RPS-3 has a voracious appetite for them. Sometimes a rubber seal will break up in a day if the rubber has hardened over time or has an excess of flash on the mould parting line. In fact it is rare to find one without any flash as the rubber production quality is very low and it is a miracle that the plant manager was not fired (or shot).
 
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As a historic note here are the front and index pages of the magazine that the RPS-3 speargun was first announced in. It was yet to become a production gun, which was only a 40 cm gun, and did not then have its designation. The article starts on page 42, "hydropneumatic gun".
 
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The all-important inner barrels with their wandering holes over the rear section of the barrel. Not a straight line anywhere, so drilled with a press and a guide and that is about all as the spacing’s are not exact with 6 holes in each set which required 3 diametrical passes of the drill bit.

 
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On Russian forum www.apox.ru there is advice that the muzzle seal in the RPS-3 can be replaced using a washer from a mixer tap cartridge such as this one. The mixer tap cartridges come in different sizes and the RPS-3 can be converted to different spear diameters by changing the size of these washers, thus as well as the standard 9 mm spear the gun can be converted to use an 8 mm shaft.
 
I measured the smaller. It has ID 8 mm and OD 13.3 mm. The measured ID is in the middle. It has cone shape inside. In the middle is the lowest ID. It seems to be quite acceptable solution for 8, 8.5 maybe 9 mm shafts.
 
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I have often referred to the rubber seals of the RPS-3 as being rubbish and here you can see some unused ones from the bag of spares supplied with each gun. To call them "O" rings would be a stretch of the imagination. They served as packing pieces which function by stuffing all the available open space to stop leaks so that there are no gaps. However the heavy peripheral flash which rivals Saturn’s rings tends to get rolled up as the pieces are assembled making undoing them a job for Samson as the rubber twists into tangled shapes which can never be replaced as they were when they came out, which means they have to be replaced. The plastic backing washers for the muzzle seals are not too bad, but the hole in them is not right in the centre! Thus while the metal workers did a good job in machining all the complicated parts of the RPS-3 they were let down by the guys in the plant making the rubber and plastic parts.

Note the muzzle seals are meant to be a rounded corner, rectangular cross section rather than a circle as you have with an "O" ring, but they are only able to approximate that shape once done up tightly with the spear in place and worn in. However they rarely lasted long enough for that change in shape to occur as the stresses imposed broke them up before they could conform and if you put oil on them then they would swell up like bullfrogs and lose all mechanical strength. All the rubber parts shared this property, including the seal on the sliding shaft that operates the trigger mechanism and you only received four of those as spares.

Rubber ring (spare muzzle to spear shaft seals) 40 pieces

"O" ring diameter 3.6 mm 4 pieces

"O" ring diameter 23.5 mm 4 pieces

Washer (plastic backing washer for the muzzle rubber seal) 10 pieces
 
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Your ideas about the work of water in the RPS3 gun are a little incorrect! Water replaces the volume of the harpoon and flows from holes in a certain area are encountered creating turbulence leading to additional losses!
 
The intention of the diagram is to show that water cannot flow if there is no space below the hole and it is full of water. If you remove the tank from an RPS-3, fill the barrel with water and load the spear then you can see the collapse of the rubber pipe as the spear moves forwards. This is somewhat difficult to do as you also have to hold the gun together to keep the inner barrel in the gun. One hand holds the muzzle, pulling it backwards, the other hand holds the spear. If you use the pump handle on the spear's threaded tip this then provides a good grip as the RPS-3 uses the spare spear shaft for the pump rod. The RPS-3 is held together by its outer tank, not the inner barrel tube which is in a sense free-floating and trapped between the bulkheads front and rear.


This test shows if the ties on the rubber pipe are good at each end as well as the inner barrel to bulkhead sealing. If water is lost then it will go into the air reservoir space, not so good!
 
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Here are the tiny parts of the RPS-3 trigger mechanism which is an ingenious design that holds the spear in the charged to shoot gun by virtually a sliver of metal, it needs to be precision made or it will not work. Unfortunately the manufacturer made the parts out of rust resistant metal rather than stainless steel, however the highly loaded parts would need to be made of hard stuff as mere millimetres hold the spear tail in the charged up gun. Owners received a spare spear tail as sooner or later the tapered on either side tail ridge, basically the spear tail notch in terms of its function, would wear down, although rotation as it probably settled in a new position each time spread the effects of wear out.


Note the flat black plastic washer on the rear end of the bolt presses the rubber ring that seals the shaft of the bolt into a bulkhead as it slides and activates the sear release system by moving fore and aft through the bulkhead. A near identical bolt, but not hollow, at the other end of the sliding element simultaneously unlocks the line release finger at the upper rear of the gun when it shoots. Only problem is if the adjustment is out, which is achieved by adjusting the lengths of the bolts by screwing them in or out, then the line release stays locked, the shooting line snaps and your spear may be lost!

This elaborate but highly stressed trigger mechanism is the most interesting part of the gun, and must win the prize for the most unlikely trigger design ever used in the history of spearfishing. A big effort was expended to make it work which may have been better spent on the rest of the gun.
 
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Here are the parts of the trigger mechanism which are plated for (inadequate) protection. The trigger hook and line release finger are (poorly) chrome plated as is the front hollow bolt that is made from chromed brass. The reason that the bolt is hollow is that if you press the trigger forwards instead of rearwards some tiny holes in the side of the bolt pass through the rear rubber seal that the bolt slides through and allow water to escape from the inner barrel thus reducing the power of the shot. Use this feature too often and those tiny holes eventually nibble out the seal’s inner surface and ruin it thus requiring the seal to be replaced or the gun will never hold hydrostatic pressure for the shot.

 
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