Testing the Salvimar Pneumatics

[Gazz]

Gazz, had you been using something to lubricate the seal, grease, silicone grease.., at least every few days?
That would be maybe helpful.

No i never lubricated it, i assumed the sea water was enough.
I will dip the end of the gasket in silicone grease before each dive from now on.

3 Gaskets arrived from salvimar mid week, so my vuotos back in action. (well until the 12ft swell settles down).

 

[istriker22]

Pictures of another gasket on a mares cyrano 970.

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[popgun pete]

The interior of the sectioned/sliced vacuum cuff does not appear to be scratched; the damage looks to be exterior scuffing and tearing of the wall of the nozzle section. The depth (increased ambient pressure) effect that you are talking about may pose problems, I actually made reference to it in the "Taimen" thread, but here it looks like the shaft tail stop's squared edge step is hooking the sealing lip on the exit from the muzzle. Part of the problem may be the thick rubber part immediately adjoining the sealing lip is expected to cope with two shaft diameters, 7 mm and 8 mm. If the squared edge shaft step hits the sealing lip opening evenly, i.e. all around its periphery, then it may push through without damaging the lip, but as soon as it catches on one side it will pull the nozzle section forwards and jam it against the exit hole in the forward muzzle body. That impact nips a piece out of the front of the rubber cuff which I have circled in yellow on the photos.

 

[popgun pete]

Pictures of another gasket on a mares cyrano 970.
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Your "Cyrano" is fitted with the Salvimar muzzle? Could you cut the seal in half as Gazz has done and post a similar photo. I am also interested in the external scuffing on the seal, it appears as a dulled surface in your photo above. Does the scuffing go right around the nose of the seal, or is it just on one side?

 

[popgun pete]

No i never lubricated it, i assumed the sea water was enough.
I will dip the end of the gasket in silicone grease before each dive from now on.

3 Gaskets arrived from salvimar mid week, so my vuotos back in action. (well until the 12ft swell settles down).

Only use grease on the vacuum seal if you go diving from a boat and keep away from the sandy bottom. I removed all grease from my "Taimen" muzzle as sand particles stuck to the grease, fortunately I did this before any of them got transported into the gun's inner barrel during shaft loading. Just oil it, the oil will float off in the water eventually and the rubber will be wetted as surface tension effects break down. I note after a long dive my old rubber fins used to look brand new as an unbroken film of water covered them completely until they began to dry off, whereas initially water tends to bead in droplets on fins as they emerge from the water after only a short dip. I prefer rubber fins, but that is because I have always used them around the rocks.

 

[tromic]

Pictures of another gasket on a mares cyrano 970. View attachment 39009
....
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It seems to me that neither you anointed seal? Were there no instructions when you bought a kit to have the seal lubricated?

 

[tromic]

Superior design of the vacuum cuff and its auto-axially aligned seating in the muzzle body of the "Taimen" gun can be seen here. Contrast this with the apparently poorly thought out wall thickness of the Salvimar muzzle seal!
View attachment 38994

Gasket in Salvimar kit is also auto-axially aligned, but the shaft is not nearly good aligned as in Taimen.

 

[istriker22]

It seems to me that neither you anointed seal? Were there no instructions when you bought a kit to have the seal lubricated?

I did not lubricate the gasket before installing it on the cyrano. There were no instructions to do so. However, I already replaced the gasket on the vuotto and the cyrano, with plenty of grease.

Salvimar's response was to never load the gun out of the water. Not even an offer to send me new gaskets.


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[tromic]

I did not lubricate the gasket before installing it on the cyrano. There were no instructions to do so. However, I already replaced the gasket on the vuotto and the cyrano, with plenty of grease.

Salvimar's response was to never load the gun out of the water. Not even an offer to send me new gaskets.


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Thanks!
It is also helpful to rinse the muzzle in tap water after usage.

 

[popgun pete]

Salvimar's response was to never load the gun out of the water.
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The idea behind this is that water already inside the muzzle when the gun is loaded under water will help push the sealing lip on the vacuum cuff open when the piston arrives back at the muzzle shock absorber. Any slight excess of water volume above the accommodation space in the muzzle will open the sealing lip before the shaft tail stop hits, but the two actions will usually be taking place at nearly the same instant. Any "excess" comes from the shock absorber telescoping under impact as at the commencement of muzzle loading it will be in the rest position, which is determined by unloaded gun pressure. That is the theory anyway of the proponents of this system.

 

[popgun pete]

Gasket in Salvimar kit is also auto-axially aligned, but the shaft is not nearly good aligned as in Taimen.

Thanks for this photo, the cross-sectioned muzzle photo never showed how far up that inner rim projected into the vacuum cuff body. Is the vacuum cuff a tight or press on fit on that inner rim? I only ask because the vacuum cuff seems tilted in that muzzle photo, but then it is not fully pushed back and is only sitting loosely on the remaining semi-circle of the inner rim in the sectioned muzzle body.

What I have been looking for is some pattern to the failures. If scuffing and damage is distributed all around the nose of the vacuum cuff then there is no evidence of the shaft stop diameter catching one side of the lip. The cuff fails (the body or nozzle section tears) and then one side of the lip is nipped and torn at random. But if scuffing is confined to one side (or one half) then repeated damage eventually tears the vacuum cuff on that side which would indicate that the vacuum cuff is biased to one side with respect to the shaft passing through it. Only by examining the evidence can a mechanism of failure be identified, or at least a reasonable guess as to what is going on. For sure Salvimar have lots of these guns in service, so what is wrong with these ones or are they only the ones which we are hearing about.

 

[tromic]

Thanks for this photo, the cross-sectioned muzzle photo never showed how far up that inner rim projected into the vacuum cuff body. Is the vacuum cuff a tight or press on fit on that inner rim? I only ask because the vacuum cuff seems tilted in that muzzle photo, but then it is not fully pushed back and is only sitting loosely on the remaining semi-circle of the inner rim in the sectioned muzzle body.

What I have been looking for is some pattern to the failures. If scuffing and damage is distributed all around the nose of the vacuum cuff then there is no evidence of the shaft stop diameter catching one side of the lip. The cuff fails (the body or nozzle section tears) and then one side of the lip is nipped and torn at random. But if scuffing is confined to one side (or one half) then repeated damage eventually tears the vacuum cuff on that side which would indicate that the vacuum cuff is biased to one side with respect to the shaft passing through it. Only by examining the evidence can a mechanism of failure be identified, or at least a reasonable guess as to what is going on. For sure Salvimar have lots of these guns in service, so what is wrong with these ones or are they only the ones which we are hearing about.

I am convinced that the main reason, as I stated earlier (http://forums.deeperblue.com/threads/testing-the-salvimar-pneumatics.100351/page-2#post-934214), is the external water pressure that squeezes the seal around the shaft so it is harder to get out. In doing so, each time the rubber is stretched before the spear is released. Only lubrication can facilitate drawing spear and reduce stretching of sealing rubber cuff. Poor centering of the shaft helps in damaging the sealing cuff.

 

[popgun pete]

However the vacuum cuff is pulled forwards, and I am not entirely convinced that it is because the vacuum cuff nozzle section collapses around the shaft, it appears that there is nothing to stop the nozzle extending far enough to eventually break it. Of course I am assuming that the guns were shot wet and water in the muzzle entrance was not tipped out of the muzzle before inserting the shaft tail. At the end of the shot the trapped water in the muzzle "accommodation space" re-expands the nozzle back to shape. If you look at the "Taimen" schematic you can see if the nozzle part stretches it can only go so far forwards due to the step in the muzzle sitting directly in front of it. Maybe the hole in front of the Salvimar vacuum cuff is too big, especially as it has to pass through two shaft sizes. It may work better with the 8 mm shaft, but the front of the seal's tapered exterior seems to be beat up by the exit hole in front of it, judging by the scuff marks seen in the photos.

 

[tromic]

Of course, high degree of damage of sealing cuff as on images, is not from ambient pressure of water. The cause of such a damage is water already in barrel from previous tiny damages. On shooting water in front of piston pushes the cuff to expand forward and it is being pinched between the shaft tail and the muzzle body, being plucked. But ambient pressure might help in premature damage of sealing cuff if it is not greasy so friction is higher during passing the shaft by it.

 

[popgun pete]

Well that sentence was actually saying "However the vacuum cuff is pulled forwards, and I am not entirely convinced that it is because the vacuum cuff nozzle section collapses around the shaft and increases any overlap between the parts causing them to catch even more". The shaft step will cause the nozzle section of the cuff to be dragged forwards, but the point I was making was that the extent of the overlap will diminish back to what it was before pushing on the hand loader commenced. Overlap as in transverse to the bore axis.

 

[tromic]

Well that sentence was actually saying "However the vacuum cuff is pulled forwards, and I am not entirely convinced that it is because the vacuum cuff nozzle section collapses around the shaft and increases any overlap between the parts causing them to catch even more". The shaft step will cause the nozzle section of the cuff to be dragged forwards, but the point I was making was that the extent of the overlap will diminish back to what it was before pushing on the hand loader commenced. Overlap as in transverse to the bore axis.

Dragged forwards - diminish back action, repeated numerous times can cause rupture in sealing cuff rubber body. That is what I had on mind. Also wear/damage of sealing lip is possible during passing by of shafts tail step especially because the shaft is not well centered. After barrel being flooded latter higher degree damage occurs very soon. I have ordered one Salvimar kit so I will know more when I get it.

 

[popgun pete]

How those circumferential grooves/cuts which appear in the vacuum cuff nozzle section's exterior surface may be explained is if the inner barrel leaks when the gun is cocked and the water volume exceeds the muzzle "accommodation space" water volume (refer the new diagram) then the excess water cannot escape the outwardly opening sealing lip quickly enough and it "overinflates" the vacuum cuff driving its outer walls onto the edges marked with red circles. These edges, actually a ring, probably carve those grooves indicated earlier. So they are a consequence of shooting an already leaking vacuum cuff, in other words they are post-lip failure damage, but before the nozzle body tears occur as once torn the vacuum cuff should not inflate radially to push against those edges. But maybe if the water volume is excessive, such as the inner barrel nearly full of water, then the cuff wall may still reach radially outwards to those sharp edges as even the tears cannot cope with releasing the extra water volume. The marks indicated with an arrow are in the right place.

 

[tromic]

Nice image!
I agree, it is a possible scenario. But what cause the previous damage of lips?
Here is a schematic, upper is Salvimar, the lower is UBL.
UBL seems to have more free space forvard for the sealing cuff to expand and it is for one shaft OD only (better centering). Also the front end of the sealing cuff is shorter protruding the inner support - less affected by surrounding water pressure.

 

[Jegwan]

Thanks for this photo, the cross-sectioned muzzle photo never showed how far up that inner rim projected into the vacuum cuff body. Is the vacuum cuff a tight or press on fit on that inner rim? I only ask because the vacuum cuff seems tilted in that muzzle photo, but then it is not fully pushed back and is only sitting loosely on the remaining semi-circle of the inner rim in the sectioned muzzle body.

What I have been looking for is some pattern to the failures. If scuffing and damage is distributed all around the nose of the vacuum cuff then there is no evidence of the shaft stop diameter catching one side of the lip. The cuff fails (the body or nozzle section tears) and then one side of the lip is nipped and torn at random. But if scuffing is confined to one side (or one half) then repeated damage eventually tears the vacuum cuff on that side which would indicate that the vacuum cuff is biased to one side with respect to the shaft passing through it. Only by examining the evidence can a mechanism of failure be identified, or at least a reasonable guess as to what is going on. For sure Salvimar have lots of these guns in service, so what is wrong with these ones or are they only the ones which we are hearing about.

Hi,
I use the Salvimar Vuoto muzzle on a Mares Mirage with both 7mm shaft with tang and 8mm free shaft. I have machine polished the shafts and tang. No lubrication other than sea water. I always wait to insert the shaft and load until the gun is under water. Still on the first cuff and no problems with it so far.
Jégwan

 

[tromic]

Hi,
I use the Salvimar Vuoto muzzle on a Mares Mirage with both 7mm shaft with tang and 8mm free shaft. I have machine polished the shafts and tang. No lubrication other than sea water. I always wait to insert the shaft and load until the gun is under water. Still on the first cuff and no problems with it so far.
Jégwan

I am glad to hear that. Italians are also happy with it. Maybe there is really not a problem except in a few cases?