Hydro/pneumatic gun

[popgun pete]

Adjustment diagram showing how the small bolts in the trigger slide can provide a small delay in the trigger pull discharging the RPS-3, in which time the line release blocking cam can be moved to free the sprung loaded line release finger. When the spear leaves the gun the shooting line can then overcome the wire torsion biasing spring on this lever and tip the line release finger forwards which will cause it to disappear into the frame of the gun's rear body. If it is not free to move then the shooting line will probably break and the spear will be lost as the 9 mm diameter spear has considerable momentum. After the shot the line release finger returns to its usual position sticking up at the rear of the gun, as these Soviet-era guns carry their line wraps along the top of the gun body.

 

[popgun pete]

This thread has pretty well ransacked every nuance of the RPS-3 hydropneumatic gun, but I was recently looking at the Russian patent for the gun wondering what the second page is all about as it is illegible with a terrible quality scan of the text.

Looking at the patent diagram and pumping up its size while knowing what the final product looked like it is now apparent what that second page said.

Originally the idea was for the trigger to pull the trigger rod shown in blue out from under the tail of the sear or release lever shown in red. The angled mushroom head on the spear tail is trying to push the sear lever aside, but it cannot budge while the trigger rod’s front pin is stuck under its rear end. Once that sliding pin is withdrawn by pulling the trigger then the spear can fly from the gun. In figure 2, which is a slight enlargement of the trigger operating system, it is showing if you pull the trigger back distance "a" the gun shoots, but if you reverse the direction and push the rod forwards distance "b" then tiny radial holes in the rod send water back from the hydrostatic pressure area via a hollow in the sliding trigger rod body and pin. Note that using that depressurising system to vary the power of the shot and you will eventually nibble the seal on the slim rod out. This was probably easier to draw than to make so they created the compact laterally displaced sear disc instead which has been covered previously on this thread Then just to add to complexity they added the safety system with the rocking bar which is actuated by pushing a curved element forwards that looks like a second trigger in the final gun.

Figure 3 shows a section through the rubber ring inlet valve that allows air to be pumped into the gun. The air release screw was added later and is not shown. An awl can be used to depress the rubber ring valve, but you risk putting a hole in it.

What is interesting is that this original sear lever is very much like the one used in the Omer Airbalete, One Air and Omer XII guns, except you push a pin forwards to fire those guns near the gun's periphery rather than withdraw a pin on the centreline. This is because Omer needed to attach the air hand pump from the rear end, something that you cannot do with a trigger mechanism in the way on the gun’s centreline.

 

[Zahar]

USSR patent! Not Russia! These are different countries!

 

[popgun pete]

USSR patent! Not Russia! These are different countries!

Well they are now, but isn’t this a Soviet Patent, you can see it on the previous page. Actually many of the Soviet era spearguns were made in Ukraine, such as the Torpedero clones, the RPS-5 and various arbaletes and spring guns. The Arsenal factory made many guns. Hopefully once the Putin era ends things can get back to normal. I believe Pelengas moved much of their stock and equipment, but I don’t know if they are still operating. The Pelengas store guy is still selling guns, but some are Salvimar models, although a few Pelengas guns are available.

 

[popgun pete]

This much simpler drawing lends itself to where the water goes when the gun is cocked to shoot, water being shown in light blue. Air pressure in the tank squeezes the rubber pipe bound at each end onto the multi-ported inner barrel tube and wants to push the spear out. If the water under pressure escapes through the critical seal in the muzzle, which the user will be oblivious to in the water, pulling the trigger will result in no shot and a very exasperated spearfisherman. When the gun works properly it is very silent and ideal for shooting fish in a shoal swimming in a lake.

 

[popgun pete]

Note that the biasing spring on the "red" sear lever above is of the same type as used here on the final gun. These thin wire leg springs are prone to rusting away.

Compare with Omer Airbalete, One Air and Omer XII.

 

[popgun pete]

It now appears that the RPS-3 speargun’s most interesting and quirky features, namely the trigger release and sear disk system and the rocking bar self-applying safety lever are not covered in the patent. So now there are two questions. Who designed them and are these features incorporated in the longer 85 cm guns? Seeing as the original Athlete Submariner magazine article diagram shows them you would think so, but the earliest guns that first drew attention to the design may not. They could be like the above patent drawing, but without ever seeing one there is no way to find out. Russian spearfishing forums have not much going on right now, probably due to the current situation, so unlikely to hear from them. Ukraine pretty much the same right now.

 

[popgun pete]

A photo showing variability in RPS-3 spear tail production. The spear when latched holds on by the tiniest sliver of metal and they will wear out even if the shaft is revolving to a new position each time which spreads the wear around their periphery. The extreme rear cylindrical part has to stick into the boss that plugs the sear disk from the rear or the spear tail will jump over the sear tooth. Think of dangling from a high window ledge literally hanging on by your fingernails! The flash chrome plated shaft on the right easily blisters with rust unless scrupulously cleaned and lubricated and the thin cadmium plated shaft on the left gets surface rust as the cadmium is consumed, but is fixable compared to the chromed shaft which goes into recycling. As the spear tails eventually wear out you get a spare one with each gun. The spear tails are made of hard stuff as they need to be! If the spear clicks into the gun and then promptly escapes your loading hand may still be in the way.

 

[popgun pete]

Recently someone asked me about this gun and I noticed some diagrams have disappeared, so here they are again.

Loading spear into gun. Trigger mechanism is in discharged state.

Spear tail is trapped by sear disk moving into center of gun and grabbing onto one side of spear tail while rear boss slides forwards to plug the rear of the sear disk and simultaneously enveloping the rear stub of the spear tail. That latter action prevents the spear tail from jumping over the tooth formed by the angled inner face in the disk. Just as well as it is only holding the spear tail by a sliver of metal.

This diagram shows how the angled ramp of the spear tail pushes the sear disk down against its small radial biasing spring with the rear boss unable to enter the back of the disk until the sear disk is centralized on the gun's longitudinal axis. Bee's dick tolerances are not replicated in the diagrams to allow clarity even though it may look like the rear boss could move.

The diagram shows the spear just entering the sear disk before any pushing occurs to displace the sear disk laterally. You can also view it as what happens when pulling the trigger which hauls the rear boss out of the back of the sear disk, the pressure from the spear tail pushes the sear disk up moving it off center and the spear then shoots out of the gun. All rather ingenious but puts a lot of load on the engaging parts. The sear disk has to slide on the washer sitting in front of it and that washer transfers the cocked gun's force into the gun body. So rather than a sear lever and a sear lever pivot pin the washer acts as a slide for the sear disk. Lubrication in the form of grease is needed, but just a touch as anything could be coming down the barrel of a dropped and discharged gun.

 

[Zahar]

Hole for air to escape from the barrel!

 

[popgun pete]

Hole for air to escape from the barrel!

That tiny hole allows water to escape when the RPS-3 gun is charged to shoot. Instead of pulling the trigger rearwards you press it forwards and the internal slide moves the front bolt forward inside the rear boss which causes the tiny radial hole in the bolt, which is hollow with an inner axial bore hole, to pass through the rear rubber seal and provide a flowpath out of the gun. That water loss decreases the power of the shot, but press the trigger forwards for too long and the gun will dump all the water that represents the spear volume injected during muzzle loading and the gun will then not shoot. If that happens then you have to pull the spear out of the gun by hand while pulling the trigger. Frequent use of this power controller tears up the rear rubber seal and the gun leaks and will not keep hydrostatic pressure as the radial hole, although tiny, tears up the inner running surface of the seal which is a rubber packing. If it was an "O" ring then it would be ruined even faster. I damaged that seal when checking out the gun and I didn't move it that many times and the gun was wet to provide lubrication. The guns are supplied with spare seals, but if you want any life out of them then don't use the power regulator.

The adjustable power setting is shown on the second slide position on the diagram shown at post #101 above. It shows a forward arrow on the front bolt. Note that the front and rear bolts are the screw adjustments to get the gun shooting after the line release is freed, get it wrong and the shaft will take off and the immobile line release will bust the shooting line, the spear probably never to be seen again on a weedy bottom.

 

[popgun pete]

The RSP-3 has an attractive appearance and intriguing layout, so speargun builders have tried to modify it by getting rid of the rubber hose used as a flexible moving pressure bulkhead and the ported inner barrel which has been drilled out like a sieve and is full of tiny holes. To retain it as a hydropneumatic gun a moving annular coaxial bulkhead and smooth inner barrel has replaced the original parts, but then the air reservoir has to have the air inlet moved to the muzzle as it cannot use the existing air inlet position in the middle of the gun. To make use of the existing air inlet position the gun can be transformed into a pneumatic with a sliding piston, new inner barrel and a new shock absorber equipped muzzle, but that reduces the power stroke of the gun due to the piston length. With the gun's overall length already being occupied by the long internal slide and trigger system at the flooding rear end of the gun it is much longer than it needs to be if it used a more conventional system, so in my view it is not worth changing and is best kept as it was originally intended. The original rubber seals are only fit for the trash bin if you plan to use it as the rubber used is not up to the job with bad oil swell characteristics and being prone to fracturing.

Interestingly its original rival which also has a vertical sliding sear tooth, but as a column rather than a moving disk, the Scorpion which became the Taimen is still in production. Because the external trigger directly pushes up on the column which is biased downwards by the gun's internal pressure, everything is much more compact than in the RPS-3. Similarly using machined alloy rear parts, the Taimen benefits by a big plastic rear handle with an internal buoyancy element that makes the gun a floater after the shot.