Zelinka System Titanium floating gun on eBay!

[Diving Gecko]

Here's a video with a few seconds showing what Pete talked about in terms of unscrewing the muzzle a bit when pumping:


What I wasn't sure of is how much of a friction fit there is between the tail end and the piston. It looks like a straight shank on most Zelinka shafts, I have seen so was confused about how the piston would be pulled back out on the return stroke of the pumping action. But maybe there is quite a bit of friction, still.

Just now, on a webshop, I did find one piston which is made only for pumping - for a shaft to thread into, I reckon - but it seems this approach is not used widely:

Also, here is one more. I think it is from a video of a visit to a DIYer or perhaps a master builder, so probably not mass manufactured:

The upper assembly shows, I think, a shaft screwed into a pumping piston. But it also gives a good indication of why these Zelinka guns are considered very efficient: There is very little room for water in the barrel. It's common to use 7mm (sometimes 8mm) shafts and the barrel tends to be 10mm. I guess it has been like this since the early days of the Zelinka guns and compare that with Italian guns which mostly used 13mm barrels and took decades to introduce 11mm barrels.

Add to that a whole lot longer efficient piston travel in a Zelinka barrel, perhaps 80mm longer than in a normal Italian gun and you begin to see how these guns are said to easily outshoot their Italian counterparts. Especially in the smaller sizes commonly used in the ex-USSR.

The stainless steel barrel also has a huge following. I think since it is believed to have a lot less friction and it seems that when the manufacturers want to make a budget Zelinka they try hard to still keep the stainless barrel and swap out other parts for alu/Duralumin.
Dima (UBL) has a video showing a lot less friction in a steel barrel but the test shows friction of the piston to break free from a standstill. That’s called static friction and though it may be many times higher on an alu barrel it may not mean it’s that bad once the piston starts moving (dynamic friction). No matter what, the “Eastern Block” builders seem to swear by stainless steel barrels.
I wonder if anyone has done tests on dynamic friction with a moving piston between different types of barrels?

 

[popgun pete]

When using the spear shaft for the pump rod the nose end of the spear is the rear of the pump rod, in other words the spear is used back to front. The Pelengas Zelinka was supplied with an integral tip shaft with a screw on point, but the flopper would carve up the barrel bore if that shaft was used as a pump rod, fortunately the gun has its own hand pump as I said before. If parts screw off then shafts can double as pump rods using the hand loader as the pump handle. Some hand loaders are a short metal tube with a transverse hole in the center. The spear point goes in the larger hole and directly opposite on the same diameter is a very tiny hole that the extreme point sticks into so that the loader is stable. Actually they make for good hand loaders as they ain't going to break!

 

[popgun pete]

I watched that video right through (about 8 minutes) and it is quite good. At first you might think that there are not that many parts to a Zelinka, but that is because many of them are very small. By way of comparison there is nothing to a "Sten", especially one without a power regulator!

 

[popgun pete]

Here's a video with a few seconds showing what Pete talked about in terms of unscrewing the muzzle a bit when pumping:


What I wasn't sure of is how much of a friction fit there is between the tail end and the piston. It looks like a straight shank on most Zelinka shafts, I have seen so was confused about how the piston would be pulled back out on the return stroke of the pumping action. But maybe there is quite a bit of friction, still.

Just now, on a webshop, I did find one piston which is made only for pumping - for a shaft to thread into, I reckon - but it seems this approach is not used widely:
View attachment 54824

Also, here is one more. I think it is from a video of a visit to a DIYer or perhaps a master builder, so probably not mass manufactured:
View attachment 54825

The upper assembly shows, I think, a shaft screwed into a pumping piston. But it also gives a good indication of why these Zelinka guns are considered very efficient: There is very little room for water in the barrel. It's common to use 7mm (sometimes 8mm) shafts and the barrel tends to be 10mm. I guess it has been like this since the early days of the Zelinka guns and compare that with Italian guns which mostly used 13mm barrels and took decades to introduce 11mm barrels.

Add to that a whole lot longer efficient piston travel in a Zelinka barrel, perhaps 80mm longer than in a normal Italian gun and you begin to see how these guns are said to easily outshoot their Italian counterparts. Especially in the smaller sizes commonly used in the ex-USSR.

The stainless steel barrel also has a huge following. I think since it is believed to have a lot less friction and it seems that when the manufacturers want to make a budget Zelinka they try hard to still keep the stainless barrel and swap out other parts for alu/Duralumin.
Dima (UBL) has a video showing a lot less friction in a steel barrel but the test shows friction of the piston to break free from a standstill. That’s called static friction and though it may be many times higher on an alu barrel it may not mean it’s that bad once the piston starts moving (dynamic friction). No matter what, the “Eastern Block” builders seem to swear by stainless steel barrels.
I wonder if anyone has done tests on dynamic friction with a moving piston between different types of barrels?

The stainless steel barrels are resistant to wear from grit and silt suspended in the water compared with aluminium. Spearfishing the ocean we generally have clean water and only rarely do you find yourself spearing in a suspension of sand except after heavy weather where it takes a while for smaller particles to settle out. In a river that suspended material may always persist and when you load your gun the particles go straight down the barrel and may be caught by the piston seals on the way out effectively sandpapering your inner barrel. Many Italian guns which we have no problems with tended to wear out when used in lakes, rivers and water reservoirs.

 

[Zahar]

 

[tromic]

 

[Diving Gecko]

As for the two different ways of sealing the barrel (the o-ring inside the barrel or on the rear face) I can think of one more difference besides having less force on the barrel in the rear-face sealing method. It might only be purely theoretical but let me try to explain.
One potential downside of the Zelinka design is that in order for the piston to stop at the rear of the barrel, there has to be a lip for it to stop against. This is normally done by with a bushing. In a 10mm barrel, the ID of the bushing is often 9mm.
Now, I don't know if going from 10mm to 9mm throttles the air at all but if it does then the rear-face seal may have a very tiny potential advantage. You would still need a stopper for the piston, but since you don't have to seal against the inner bore, it doesn't have to be a concentric. It could be a lip that doesn't go around full circle but just had two small flanges opposite each other and then the majority of the 10mm bore would still be unobstructed for air flow. Or just two small pins protruding 0.5-1mm transversely into the end of the barrel.
I am probably making a big thing out of nothing but it is one more reason, I one day hope to speak to a fluid dynamicist to learn more about how a reduction in aperture affects airflow and by how much.

Here are two simple sketches trying to visualize what I am talking about:
First one is the traditional design:

The inner sleeve for the valve bushing may mean that the airflow through the rear is slightly throttled (the yellow "brass" bore is ø9mm whereas the barrel itself is ø10mm)?

If so, then perhaps moving to a rear-face seal can help as you could open up the stopper lip a whole lot more:

Now, even though I think it exists, I am not sure how the rear-face seal actually works as there would be some challenges in holding the o-ring in place (see next post).

 

[Diving Gecko]

The Zelink system exists in two forms! In this figure, a loaded barrel! The force on the barrel and whispered more than the loading force of the harpoon by 12 - 14%! The second system of Zelinka - it is the same from the author of this system - the unloaded trunk! The force on the trunk and whispers is minimal but sufficient to overcome the friction forces of all O-rings involved in the movement of the barrel and varies from 6 to 12 kg!View attachment 54818

Fixed Stem Valve

Hi @Zahar I think we lost a bit in translation but can you possibly try to explain again in other words, please? Or perhaps with a drawing?
I am very interested in how the second type of valve seal functions. I may be wrong but I am guessing that the two types look like my drawings below?

Let's say that this one is the traditional one - let us call it "Inside Sealing":

Perhaps, we can call the second type for "Rear Face Sealing". Here is a very simplified drawing:

Does that second design - The Rear Face Seal - exist at all? Am I right in assuming that this is the second type you are talking about?
If so, how do you keep the o-ring in place so it doesn't fly around inside the gun? Do you have a picture or drawing of this?
And sorry to ask again, what is the advantage of this second type of design, if it exists?

I have found this drawing which looks like a Rear Face Seal but the seal (o-ring?) looks like it could be worn out very fast if it is retained and squeezed like that. Perhaps it is a gasket and not an o-ring which might help:

 

[Zahar]

As for the two different ways of sealing the barrel (the o-ring inside the barrel or on the rear face) I can think of one more difference besides having less force on the barrel in the rear-face sealing method. It might only be purely theoretical but let me try to explain.
One potential downside of the Zelinka design is that in order for the piston to stop at the rear of the barrel, there has to be a lip for it to stop against. This is normally done by with a bushing. In a 10mm barrel, the ID of the bushing is often 9mm.
Now, I don't know if going from 10mm to 9mm throttles the air at all but if it does then the rear-face seal may have a very tiny potential advantage. You would still need a stopper for the piston, but since you don't have to seal against the inner bore, it doesn't have to be a concentric. It could be a lip that doesn't go around full circle but just had two small flanges opposite each other and then the majority of the 10mm bore would still be unobstructed for air flow. Or just two small pins protruding 0.5-1mm transversely into the end of the barrel.
I am probably making a big thing out of nothing but it is one more reason, I one day hope to speak to a fluid dynamicist to learn more about how a reduction in aperture affects airflow and by how much.

Here are two simple sketches trying to visualize what I am talking about:
First one is the traditional design:
View attachment 54842

The inner sleeve for the valve bushing may mean that the airflow through the rear is slightly throttled (the yellow "brass" bore is ø9mm whereas the barrel itself is ø10mm)?

If so, then perhaps moving to a rear-face seal can help as you could open up the stopper lip a whole lot more:
View attachment 54843

Now, even though I think it exists, I am not sure how the rear-face seal actually works as there would be some challenges in holding the o-ring in place (see next post).

Such a design will create a large parasitic volume between the piston and the valve and the harpoon will travel back a third of the barrel length! Speed of sound = speed of air overflow without interrogation = 330 m) s Speed of harpoon at the exit of the gun 25 - 37 m) s All talk about pressing diameters of holes is far-fetched! That's why valve guns are made! It is common sense to make a hole at least half of the trunk section!

 

[Zahar]

Hi @Zahar I think we lost a bit in translation but can you possibly try to explain again in other words, please? Or perhaps with a drawing?
I am very interested in how the second type of valve seal functions. I may be wrong but I am guessing that the two types look like my drawings below?

Let's say that this one is the traditional one - let us call it "Inside Sealing":
View attachment 54844

Perhaps, we can call the second type for "Rear Face Sealing". Here is a very simplified drawing:
View attachment 54845

Does that second design - The Rear Face Seal - exist at all? Am I right in assuming that this is the second type you are talking about?
If so, how do you keep the o-ring in place so it doesn't fly around inside the gun? Do you have a picture or drawing of this?
And sorry to ask again, what is the advantage of this second type of design, if it exists?

I have found this drawing which looks like a Rear Face Seal but the seal (o-ring?) looks like it could be worn out very fast if it is retained and squeezed like that. Perhaps it is a gasket and not an o-ring which might help:
View attachment 54846

The wrong picture gives the wrong idea about the operation of the 0-ring valve! I hope my additions will help to understand that the 0-ring can not fly out of place! The contact forces are directed at an angle to the valve seat, and the hole is blocked by the body of the valve screw!

 

[popgun pete]

Just reflecting on the Zelinka gun some more I think the design is best suited where you are operating in murky water with abrasive particles in suspension. The gun only has one opening, the muzzle, which particles can penetrate, unlike the rear travelling valve guns where the valve or something connected to it moves rearwards. To reset these guns you have to push the tail piece forwards which again closes the valve, so you have relative movement of parts where particles may intrude, although the gaps are very small. In the Zelinka guns you can think of the rear end as completely closed off.

In the ocean you are operating in much cleaner water, hence the rear opening valve guns will not have such problems. Examples are the “Continent”, “Katran” type guns and the “Alpha C1”.

GSD in Italy made valve operated guns, but these used a system of levers to withdraw the plug valve from the rear of the inner barrel, they did not use the gun’s internal pressure to operate the releasing valve. Lots of parts and troubles when the releasing valve seats took a permanent set, so that was the end of them.