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Moving O-ring Muzzle For Large Slider Shafts (Inspired By The Seatec Evo-Air)

Diving Gecko

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Jun 24, 2008
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The Background
In preparation for a new bluewater build, I have been thinking about muzzle seals. The Vuoto/UBL seals don't fare well with 8.5-9mm shafts and I want to be able to shoot those. One way around that is to try to make my own conical vacuum cuffs from casting PU into 3D printed molds. I might still try that.
But I also started thinking about an old Evo Air muzzle that I have. That design got a bit of a bad rep in Italy but I actually really like it. Its whole claim to fame was that the o-ring would move into a larger cavity during the shot and thus greatly reduce friction. But I think it was proven that the o-ring does not actually move forward during the shot as intended - the vacuum holds it in place in the tighter o-ring groove. Personally, I think the real benefit was that it could be loaded submerged and while that feature might have been unintended, it is one that I refuse to live without.

Now, Seatec only designed the Evo Air muzzle to work with 7mm front-tied shafts, but I am thinking that the movable o-ring design might actually work for shafts with a tail end, too... Especially since Dima's tail ends are only 1mm larger in diameter than the shaft itself. So, with some careful o-ring design, keeping gaps to the bare minimum, proper testing and a bit of luck, it might actually work.
I am still not back to my machines in China, so it will take a while to try this out.

But let's start this off with some fancy renderings. All of them are missing a slide ring, but just imagine it is sitting in the bore in the red front part of the muzzle.
I started off with a design in two parts - it could be an alu rear and Delrin front:
GeckoSub_Moving_O-ring_Muzzle_14.JPG_1200PIX.JPG

The little blind hole at the top is for a DIY wrench - Dima does it this way and it's easier to fabricate for me than milling flats and also, the tool can be made really lightweight, so you don't have to travel with a real spanner.

But given that the the gaps between the inner walls and the shaft has to be kept to an absolute minimum for the o-ring not to migrate to the vacuum side I realized the two part design would likely only work with one given shaft thickness, so I drew up a more modular, three part muzzle:
GeckoSub_Moving_O-ring_Muzzle_01.JPG_1200PIX.JPG

GeckoSub_Moving_O-ring_Muzzle_03.JPEG_1200PIX.JPG


The rear part and the shock absorber could be titanium. It is not that easy for me to machine titanium but in this version, we are talking fairly simple parts, so it might be doable. The middle and front parts wont take much impact so Delrin should suffice. It is light, easy to machine and really slippery which should work well for the o-ring seat. Also, the middle and front parts could be changed out for when using different sizes of shafts - importantly, without having to depressurize the gun.
Now, let's look at the guts:
GeckoSub_Moving_O-ring_Muzzle_05.PNG_1200PIX.JPG


Finally, two screen grabs; one showing the muzzle in the loading position:
GeckoSub_Moving_O-ring_Muzzle_08.PNG_1200PIX.JPG


The red front part will be unscrewed two full turns, moving it 5mm forwards at the end of the loading process. This way, the o-ring can move forward into the bigger groove and hopefully, let the tail end through without too much friction or damaging the o-ring, So, at the end of the shot, it would look like this:
GeckoSub_Moving_O-ring_Muzzle_07.PNG_1200PIX.JPG


Now, this is just an idea and it might not work, but I am willing to try it out. Of course, the o-rings will be punished a bit but even if they only last a few days, it wouldn't be an issue changing them out on a trip or even in the boat. In the drawings above, the o-ring has a cross section of 3mm and I would think going as big as I can on the cross section would help reduce the risk of the o-ring getting sucked into the gap. On the other hand, thicker rings don't stretch as easily.
Once, I get back to China it should be fairly easy to test this concept out with some Delrin and/or 3D printed prototypes.

BTW; The three part muzzle, if made in titanium and Delrin according to this design would weigh around 55g and be 75mm long. That's 22g lighter than the Evo Air and 18mm shorter. It is also only 7g heavier and 7mm longer than a Vuoto muzzle.
 
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popgun pete

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During the shot the shaft tail step can catch and rip the surface of the "O" ring. Most spears today use a 0.5 mm step as any less and the shaft will jam in the slider or stop ring by trying to wedge it. The RPS-3 used this system and to ease the passage through the muzzle seal the spear had a spherical step and a line slide that matched so that the impact forces did not forge up any sharp ridges. Cold working of high impact areas occurs in spearguns and the resultant edges rip vacuum seals to pieces unless you file them down and leave a smooth surface to negotiate the passage through the seal. The RPS-3 system did work, but the brittle rubber used in the seals was absolute rubbish and the forces as the rounded bump passed through ripped the seals by tearing chunks out. The rubber seal needs some thickness to enable momentary compression as the fat tail bump goes through them.
spear tail spherical bump.png
RPS-3 original drawing spear tail.jpg

How the rubber nozzle type seals work is the small amount of water that is in the vacuum barrel as you load it forms a plug in front of the advancing piston and blows the nozzle open just as the spear tail arrives sending the tail step through as the sealing lip is momentarily expanded. If you tip the water out before loading then this does not happen and the sealing lip takes its chances with the edge of the shaft tail step. The Taimen buys a bit of insurance if this happens by using a polyurethane leading edge on the step which will not damage the sealing lip. As small clearances are involved the vacuum seals should be matched to the shaft diameter, anything else and the nozzle lips on the seals will be damaged eventually.

The fore-aft moving "O" ring idea after the gun is loaded will work provided that the "O" ring does not tilt in its movement. If it does not stay flat as it moves forwards then the shaft tail will makes short work of it. Possibly a sprung loaded collar could control it that the "O" ring pushed against, the spring not being too strong and the collar periphery stopping it tilting during its fore-aft bore travel.
 
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popgun pete

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Jul 30, 2008
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Something like this.
GeckoSub_Moving_O-ring_Muzzle_mod.jpg

Instead of the spring some rubber balls or rubber segments that act as a spring, but trapped so that they do not fall out of the gap.
 
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tromic

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I had already tested the same concept few years ago. I used and combined some part of various former Tomba designs just to see how long would O-ring survive. O-ring was movable too and additionally silicon greased to minimise the friction but anyway there was some damages after few shoots..
Maybe I wrote something about that under Tomba, but now I can not find that post because Tinypic images disappeared...
But anyway Davide try it, maybe you will find a solution!
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
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Besides the issue of the o-ring having to suddenly move forwards and expand when the step of the shaft tail hits it, there is the challenge of keeping the o-ring from moving into the gap between the flange it sits on and the shaft. On a freeshaft muzzle of this type, that gap can be kept very small (0.1-0.2mm would likely suffice) but since the tail end is 1mm larger in diameter than the shaft, the gap will be have to be at least that.
And during the shot, I would be afraid that the shaft would tilt slightly and the tail end hitting the flange upon exit. But I think there's a simple workaround - make the tail end long enough so that it has passed through the flange before the piston hits the shock absorber. This way, the shaft is still supported and centered and the gap can be designed to be fairly small:
GeckoSub_Moving_O-ring_Muzzle_18.PNG_1200PIX.JPG
 

popgun pete

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The most important thing is to get rid of the right angled shoulder on the stop diameter or shaft tail step. The spherical section shoulder is less likely to jam, if you use a taper instead then it will wedge on the slider. To spread the contact pressure the contacting faces should match, which takes careful machining of the parts as we are talking of a 0.5 mm step machined as a curve.
Wasp speargun spear tail.jpg
 
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popgun pete

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Just checked to see if the Seatec Evo-Air was still being sold and found it here allegedly at 50 per cent off. 45 euro is about AUD 73 or USD 50.

Copy of the advertising blurb after "poor" auto-translation. An "auction" is a spear.

EVO-AIR Vacuum Flying Kit in the sizes:

- 18x1.25 All guns such as Cressi SL, Mares Sten, Omer.

- 18x1.5 Only on Seacsub rifles

APPLICABLE TO OLEOPNEUMATIC GUNS.

USE:

1) LOADING:
THE AUCTION IS INSERTED INTO THE RINGGUN WITH A RING COMPLETELY HANDED
The o-ring has a diameter equal to that of the rod and is therefore pushed by the ring nut into a narrower seat which, by compressing it, makes it tight. watertight.


2) STAND-BY:
THE ROUND OF A TOUR IS EXPOSED AND IS EXPECTED IN THIS POSITION UNTIL THE TIME OF SHOOTING.
Once the rod is loaded, the ring nut is brought to the forward position but the o-ring remains in the narrow position continuing to generate watertightness. It is left in this position until the moment of shooting.


3) LIGHT: PRESS
THE TRIGGER
Thanks to the mobile o-ring, friction becomes NON-EXISTING. At the time of shooting, the rod immediately drags the o-ring into the wide seat, the o-ring expands and assumes the same diameter as the rod which will no longer friction on it.
 
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popgun pete

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I thought that I would order one to try it out, but only got this far with my purchase when the delivery number came up. As you can imagine the shipping cost just blew the thought of buying completely out of the water. Shipping from Italy has burnt me before, but 229 euro for shipping something this size is completely ridiculous. At current exchange rates that would be AUD 445 in total, plus 10% GST!
Seatec EVO-AIR Order.jpg

Just checking and this "Evo-Air" gadget goes back to 2010, hence probably the reason they seem to be selling for around half price now. The use of front tied spears is a turn off and maybe it is just as well that the shipping is overpriced.
 
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Diving Gecko

Diving Gecko

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Jun 24, 2008
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About The Evo-Air - And Its Use With Front-tied Shafts
Hi @popgun pete and others,

The Evo-Air was designed for front-tied shafts only. They spec it to work with 7mm, but I feel like I have used it with a 6.75mm shaft, too though I am not 100% about that. Don't ever buy one if you don't like front-tied shafts. It's also a bit heavy. That said, it works great for that purpose. It also ships with a replacement tail in Ø7mm so that you can use it on regular shafts, if you drill a hole for the shooting line yourself.
As for the price, I bought mine around Christmas 2012/13 and it was 75 Euros, but believe it dropped soon after that. Back then, it was the new kid on the block with pretty much only STC being mass produced.

I have that same instructional blurb in a PDF from Seatec :
SEATEC EVO AIR INSTRUCTIONS.PNG_1200PIX.JPG


I think the official instructions are where a lot of the hate comes from as doing it this way, you will have quite the hydro lock trying to insert the shaft into the piston. But if you don't follow the instructions and instead insert the shaft with the muzzle in the "open" position, then water will be expelled when you insert the shaft. After that, close the muzzle and finish the loading. That's what I do and why I say, it's actually a good design - despite that this is not how it was envisioned to work, haha.
Years ago, I saw a video which I have sadly not been able to find again (maybe Tomi linked to it back then). From memory, a guy had made a practical experiment showing that the friction of the shaft in the moment of the shot does not move the o-ring forward into the bigger bore - which is what Seatec claimed it would. The vacuum and pressure at depth holds the o-ring in place. For that same reason, it doesn't actually matter whether you forget to put the muzzle back in the open position before shooting.
As such, loading a gun with an Evo-Air muzzle could instead be simplified to the following:

Insert shaft into piston with muzzle in Open Position -> Close muzzle -> Finish loading -> Shoot
That's how I shot my Evo-Air towards the end, after having seen the debunking video, and it is almost the exact opposite of Seatec's instructions. Before that, I would still open the muzzle when inserting the shaft, then close it for loading the shaft to the trigger and feel bad if I had forgotten to open it again before shooting.

I would say that if you live in Europe, shoot front tied 7mm shafts and don't mind a slightly heavy muzzle, then the Evo-Air is still a good proposition. On the other hand, you can probably get a much cooler looking and lighter Tomba F for not much more money - though you might have to tip the gun out of the water before loading or, if you want to be able to load it submerged, make a slot in the tail end to let water escape (if I recall correctly).
 

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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
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Shanghai
The most important thing is to get rid of the right angled shoulder on the stop diameter or shaft tail step. The spherical section shoulder is less likely to jam, if you use a taper instead then it will wedge on the slider. To spread the contact pressure the contacting faces should match, which takes careful machining of the parts as we are talking of a 0.5 mm step machined as a curve.
View attachment 55030
I agree that a tapered step on the tail end - and a matching taper inside the slider - makes sense. I was going to ask Dima if he feels it would work with hydro braking, but haven't gotten around to it yet. I tend to collect questions for him these days as he doesn't get online as much as before so will wait until I have a few more questions for him;)
 
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popgun pete

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This might be the video that I watched earlier today.
.
It is of the prototype and appears to be introducing the concept.

Basically it uses the screw down action to immobilize the "O" ring so that you can load without doing it all in one push, but once the gun is charged to shoot the vacuum in the inner barrel holds the "O" ring in place and as the gun shoots it can be driven forwards once the vacuum decreases as the piston heads towards the muzzle. For that to happen you back the front screw off so that the "O" ring is free at the front.

If the vacuum seal breaks too soon then the spear driving forwards will be met by water rushing back down the inner barrel.
 
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Diving Gecko

Diving Gecko

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Yeah, I know the official video and it’s not the one - quite the contrary.
Take the following with a grain of salt as my memory is not great but as far as I recall, the “lost” video debunked the official statement that the o-ring moves forward into the bigger bore during the shot.
From memory, the guy who did it had made a small pressure chamber in front of the muzzle and pressurized that to imitate vacuum behind the o-ring and possibly pressure at depth, too. But I can’t recall how he “shot” the shaft, though. Maybe he had actually mounted the pressure chamber on a working gun and shot the shaft into the chamber and then checked to see that the friction of the o-ring on the shaft had not changed.


Sent from my iPhone using Tapatalk
 
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popgun pete

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The advance of nozzle seals and synchronized sealing lip expansion by a plug of residual water pushing through the rubber nozzle made this Evo-Air obsolete, these ideas being used in the Taimen in 2000. At the time Sergiy Kravchenko in the Ukraine alerted me to this gun which was not far behind the Mamba which was just beginning to attract attention. Before either of them was the Russian "Korsar", a weird looking gun that won the Red Star award, being a pneumovacuum gun.
korsar2.gif
 
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Diving Gecko

Diving Gecko

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Both yes and no. Yes, the lip seal offers advantages with slider shafts but if you are designing a muzzle to be used for front tied shafts then the Evo-Air with a very standard o-ring makes sense. No proprietary seals at all. The design could be upgraded with a front that slides in and out instead of the threaded one and it could be slimmed down quite a bit, too.

Now, for slider shafts, it may not work at all and the only reason I am contemplating it is to avoid having to make my own custom conical vac cuffs. Dima told me that while his seals might work for 8.5mm he feels that 9mm is really stretching it (pun intended). So, I am taking the liberty for now to assume it is the same for the clones made by Salvimar and Pelengas.


Sent from my iPhone using Tapatalk
 

popgun pete

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Don't forget that Taimen sell seals in 6.5 mm, 7 mm and 8 mm, they don't use a one size fits all approach. Recently the 6.5 mm option was discontinued. Cost of the seals is 135 rubles, about AUD 3.00 each. If you use the one size fits all seals on the smaller shafts then they will last longer than if used with the larger, usually 8 mm, shafts. Pelengas use the polyurethane tail bush on their 8 mm shafts, the 7 mm shafts just have normal tails for this reason.
spear tail pelengas.jpg
 
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Diving Gecko

Diving Gecko

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Don't forget that Taimen sell seals in 6.5 mm, 7 mm and 8 mm, they don't use a one size fits all approach. Recently the 6.5 mm option was discontinued. Cost of the seals is 135 rubles, about AUD 3.00 each. If you use the one size fits all seals on the smaller shafts then they will last longer than if used with the larger, usually 8 mm, shafts. Pelengas use the polyurethane tail bush on their 8 mm shafts, the 7 mm shafts just have normal tails for this reason.
View attachment 55035
To recap and get back on track, then. The Taimen seals are not an option for me as I need 8.5 - 9mm. But you mentioning them did make me check if I had missed an option from STC. I hadn't as their largest seal is for 8mm shafts, too. So, back to making my own conical vac cuffs or trying to make a moving o-ring design work.
That said, I think it will take a while before I get a chance to make these parts.

P.S. Though I, myself, was guilty of drifting this thread into nude shaft territory, I have now changed the name of the thread to better reflect that we are talking about slider shafts.
 
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tromic

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Rounded tail stop would not affect hydro braking capability.
I also had said (to the inventor of Evo Air too, Sub Fireman-Maurizio , on Italian forum ) that O-ring in Evo-Air would not be movable on shot, especially not with 3 mm cross section O-ring. Force of the water is higher than the friction the the O-ring, especially on depth.
Regarding 8.5 or 9 mm shaft I would rather apply Tomba900X design, analogous to Tomba700X. It would be better than using movable O-ring. You should only solve the problem of submerged loading, if it is not acceptable for you..?
 
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Diving Gecko

Diving Gecko

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[...]
Regarding 8.5 or 9 mm shaft I would rather apply Tomba900X design, analogous to Tomba700X. It would be better than using movable O-ring. You should only solve the problem of submerged loading, if it is not acceptable for you..?
Hi Tomi,
I have so much respect for the work you and Marko do and the skills you both have - I am just in love with the idea of the slimmest possible shaft tails and sliders. An o-ring on the shaft limits how slim you can go on the sliders though the rest of the system is great.
The submerged loading is a necessity for me, but I wouldn't mind making a slot in the shaft to get around that or some other solution.

Perhaps the right thing to do is to someday make a dummy slider the size of a Tomba and test it against a UBL slider. If there is no real performance difference, I am not at all opposed to using a Tomba muzzle.
 
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Diving Gecko

Diving Gecko

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Jun 24, 2008
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Rounded tail stop would not affect hydro braking capability.[...]
Thanks for your thoughts on the hydro braking still working with, say, a 45 degree angled step. That should definitely help.
BTW, when you tried this out, do you remember the cross section of the o-ring you used? And how much bigger was the tail end? Rounded or angled?


[...] I also had said (to the inventor of Evo Air too, Sub Fireman-Maurizio , on Italian forum ) that O-ring in Evo-Air would not be movable on shot, especially not with 3 mm cross section O-ring. Force of the water is higher than the friction the the O-ring, especially on depth. [...]
Yes, I went back and looked at some our old posts from 2013 here on this forum and you even proposed the loading process of opening the muzzle when inserting the shaft to avoid the hydro lock. I didn't read all of the posts, but I most likely got the idea from you - and yes, it certainly works in real life, too. Maurizio kept saying it didn't matter but I have read quite a few posts on the Italian forums with people getting really pissed at the hydro lock issue...
 

tromic

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Davide I just find the image of my very first TombaF on Italian forum. It had "movable" O-ring.

1571937329679.png


Tomba nnnX (Tomba700X, Tomba800X) design makes it possible to use even smaller cross section O-ring then I use today.
For Tomba700X I use O-ring 7 x 2.5 (ID x cross section). But it would be possible to use O-ring 7 x 2 mm. More than 10 years ago I had a Tomba10. It had been using 6 x 2 mm O-ring. I named it Tomba10 because the ID of the muzzle tip boring accepting the slider was 10 mm. It might be even 9 mm but in that case the slider must be made in titanium having the eye for the line welded to the body like Dima has.
 
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