New STC kit - Mongoose

[tromic]

The advantage of all the vacuum seal anchored in the muzzle guns is that they can be muzzle loaded underwater. As soon as the spear tail can push the piston back then space opens up for the water already in the muzzle opening to be sucked into the inner barrel and then the muzzle seal taking up prevents any further ingress of water into the barrel. If it does not seal then water will fill the entire inner barrel surrounding the spear. Sealed sliders that seal both on the muzzle to slider body interface and on the spear have the problem of any hydraulic lock stopping the slider fully engaging into the muzzle seal, but the slider can be sucked in as the piston moves if a slight drag by the spear seal pulls the slider back into the fully sealed position. If the slider body does not take up on the muzzle seal then the inner barrel fills with water as it courses through any annular gap.

The muzzle anchored vacuum seal guns were a hassle to change or inspect the vacuum cuff/seal until the removable muzzle nose cap guns appeared and virtually all these guns now work this way. The nozzle type seals have the ability to blow open by the rubber nozzle stretching when trapped water has to get out if any water leaked in which exceeded the spear tail insertion starting volume capacity, the washer type seals with less capability to spread will not let excess water out so easily. The nozzle type seal has more flexibility to let the spear tail stop out by stretching the nozzle, but both seal types can be damaged by burrs setting up on the spear tail stop's leading edge as the spear leaves the gun which will then tear up the sealing rubber surfaces.

As muzzle loading is done at a relatively slower rate compared with the shaft exit velocity the sealing lips then have more time to conform to the changing diameters as the spear tails are pushed through them. A tiny amount of water briefly leaking in which elevates the water volume trapped inside the inner barrel above the spear tail insertion starting volume capacity has the advantage of blowing the nozzle open just before the spear tail stops diameter actually hits it, but this cannot be relied on to happen with every shot.

View attachment 58195

I do not know what type of seal has the STC mongoose - x as muzzle to slider body seal..?
I suppose it could be loaded under water... That could be the main difference/ improvement to Tomba7N7 design.

 

[popgun pete]

I have not looked at the STC website since this thread started, but I just revisited it today and there is a little more information compared with before. I now realise why they cited their earlier patent as these Mongoose designs relate to the front cap variations on their X-Power muzzle. I don’t think these changes are patented because they are borrowed ideas. The newer diagrams are shown below. Their X-Power muzzle started out as a muzzle anchored vacuum seal and because they used bare tail spears initially these don't have a slider. When you have a slider you need a tail stop on the shaft and so the curved leading edge tail stops were produced with a cupped face stop washer designed to not hammer up the leading edge of the tail stop. This tail seemed to be used with their muzzle anchored seal design and you can see it on the Cressi Saetta Pro. The Mongoose is a change to make this muzzle a sealed slider system with two seals, one on the shaft and one on the muzzle to slider surface interface. There is a third seal that enables you to pull the slider body apart for servicing the shaft seal which keeps the body join sealed. The nose cap can be undone with the fingers as it is now a plastic product with indentations as can be seen in the last photo. My guess is they rely on the muzzle cap entrance bore to hold the slider until the vacuum created by loading the shaft sucks it further back into the muzzle cap.

Note the system still needs a front slider in addition that the shooting line is attached to, so the spear carries two sliders with only the rear one being sealed.

 

[tromic]

'Shaft Kit' Mongoose for standard shafts... the 3rd way

It is a complete kit dedicated to ’X-Power’ 2.0 and 3 0 consisting of two elements in acetal
resin. In the front there is space for the compartment to accommodate the titanium shutter
and the seal (OR) while the lower part acts as a ’floor' for the seal housed in the upper
module The terminal may be disassembled and inspected at any time to verify the integrity
of the sealing element There is no need for specific tools to disassemble the terminal just
unscrew the first part of the terminal to proceed with the inspection of the section containing
the OR seal All operations can be performed with the gun unarmed and under pressure, to
allow the spearfisherman not to interrupt the fishing journey.

Thanks for additional info from STC site. I have not seen it yet. It seems to me that the speargun with this kit
can not be loaded under water. It is a bit strange because other STC configurations could be used under water. I thought there was something different from O-ring that facilitates under water loading. Maybe there is something additional not mentioned here that makes possible under water loading....?
Tomba700X could be loaded under water despite is has two O-rings for sealing. But it is better to load it above water surface.

 

[popgun pete]

It is possible it works this way to get around the hydraulic lock. If you push the rear part of the slider (C on diagram above) into the muzzle nose the water that is trapped as the muzzle to slider body seal takes up on the slider sends the front (A on the diagram) part of the slider body forwards travelling on the inner "O" ring slipping on the bore inside rear part C. The central "O" ring (B on the diagram) will move forward with it. Once you start to push the piston back the developing vacuum inside the inner barrel will pull front part A and "O" ring B back inside the rear part C. This makes sense of STC calling this two piece titanium part a "dynamic shutter". For this to work you need to push on rear part C when pressing the slider into the muzzle after jamming the spear tail into the muzzle opening, i.e. into the front of the piston. By doing this you leave front part A free to move inside rear part C and with it the shaft sealing "O" ring B.

 

[popgun pete]

Note that in engineering this "dynamic shutter" STC would have needed to make sure the stroke available in the telescoping slider body was enough to contain the volume of water that was displaced when the back end of the slider was fully inserted into the muzzle. Otherwise front part A's "O" ring would have popped out of rear section C and the sealing action would be lost. No wonder they made it out of titanium as this slider is much larger than say the hydraulic damper type made by Pelengas such as this one.

 

[tromic]

From the image of A part of titanium Dynamic Shutter it seems to me there is one additional O-ring on it, not mentioned in description..?
I agree, that might be the solution, how you explained it. Maybe that is why the Shutter is relatively long. The same idea but on different place I had applied in Tomba700X design. That makes possible under water loading using O-rings as a seal. I am curious how heavy are all that "sliders" on the shaft, together..?
My attitudes were not to be more than 3 g (cone stainless steel ring, O-ring, and the slider). The weigh of Pelengas titanium slider having hydro damper possibility is OK if it is only 1.86 g.

 

[popgun pete]

They would need to tell the user not to push on the front of the slider, at least when finally pushing it home into the muzzle. One advantage would the front part A retracting and the gap at the join disappearing would be an indication of a vacuum being formed in the inner barrel, but it would not tell you if later there was a slow leak and the vacuum was being lost.

 

[tromic]

They would need to tell the user not to push on the front of the slider, at least when finally pushing it home into the muzzle. One advantage would the front part A retracting and the gap at the join disappearing would be an indication of a vacuum being formed in the inner barrel, but it would not tell you if later there was a slow leak and the vacuum was being lost.

I suppose there is also a washer type seal in the muzzle, so they have two vacuum seals for the shaft present...

 

[tromic]

This is how Dynamic Shutter might look inside. I took the measures from number of pixels on image and making some assumptions.
A suppose the weight of titanium shatter is about 4,5 - 5 g. If I am not wrong it is not very light on the shaft especially together with the regular line slide with additional about 2.5 g. The volume of water it can receive is maybe about 1.6 ml what is enough to push the shutter maybe 7 mm deep after contact with the sealing O-ring between muzzle and the shutter.

I just find that the titanium shutter is 3 g..? On this image the O-ring is also visible inside the hosing for the shutter.

 

[tromic]

Transformation from Tomba7N7 to Mongoose-X...
This small transformation enables loading the speargun submerged in water.
Useful simple improvement...

 

[popgun pete]

Although it is not entirely clear from the photos this is what you are looking at. The muzzle to slider "O" ring also seals those two black acetal plastic parts by them clamping together on the "O" ring to form a gasket on the opposing flat faces.

 

[tromic]

Your annotation on the image is useful for better understanding. I am not sure if it was a good solution to use the same O-ring for two different sealing purposes. Usually O-ring should have a sufficient gap so it can be expanded under compression when inserting the shutter.

 

[popgun pete]

Your annotation on the image is useful for better understanding. I am not sure if it was a good solution to use the same O-ring for two different sealing purposes. Usually O-ring should have a sufficient gap so it can be expanded under compression when inserting the shutter.

I think they have done it that way to make replacement very easy as you do not have to hook the "O" ring out of an internal groove, you just squeeze it into the back of the front cap and then do it up to trap it in place.

 

[tromic]

I think they have done it that way to make replacement very easy as you do not have to hook the "O" ring out of an internal groove, you just squeeze it into the back of the front cap and then do it up to trap it in place.

I actually do not understand why STC made this Mongoose-X kit? They already have sealing of he shaft with D.S.S dynamic seal (washer type seal).
This way they made the thing more complicated - or reliable(?), having two shaft seals. That long composition on the shaft - titanium shutter, line slide, is somewhat strange to me.

 

[popgun pete]

I actually do not understand why STC made this Mongoose-X kit? They already have sealing of he shaft with D.S.S dynamic seal (washer type seal).
This way they made the thing more complicated - or reliable(?), having two shaft seals. That long composition on the shaft - titanium shutter, line slide, is somewhat strange to me.

The lack of a diagram makes me think that this kit is just using the rear body of the X-Power muzzle and its shock absorber and the D.S.S. seal is not even used. So they have converted the X-Power muzzle to an "O" ring seal based type by putting a new front end on it. I think they still have a metal bulkhead that the shock absorber leans on and that these new plastic parts screw into it. The outer "O" ring on the step in the rear plastic part probably seals the plastic front end into that rear metal bulkhead, but I don’t recall seeing any photos of it. The bulkhead would need to be metal or piston impacts would blow any front section out of the muzzle.

 

[tromic]

The lack of a diagram makes me think that this kit is just using the rear body of the X-Power muzzle and its shock absorber and the D.S.S. seal is not even used. So they have converted the X-Power muzzle to an "O" ring seal based type by putting a new front end on it. I think they still have a metal bulkhead that the shock absorber leans on and that these new plastic parts screw into it. The outer "O" ring on the step in the rear plastic part probably seals the plastic front end into that rear metal bulkhead, but I don’t recall seeing any photos of it. The bulkhead would need to be metal or piston impacts would blow any front section out of the muzzle.

I suppose there is not a lot of users of the that kit because I could not find any video or review about it.

 

[popgun pete]

I suppose there is not a lot of users of the that kit because I could not find any video or review about it.

It does not help that there are no explanations about exactly how it works or more detail on the layout as having your customers figure it out may have them look elsewhere. As observed earlier it is not really covered by their patent which is washer vacuum seal based. In a way it is now a Mamba system, but with the improvement of the telescoping “”dynamic shutter” slider to get around the hydraulic lock which was a problem with the Mamba. Another Mamba system used today is the LG-Sub speargun, but it introduced the new “Black Head” muzzle update to create a muzzle body valve that eliminates hydraulic lock. That system uses an X-ring in the muzzle to slider seal interface. Earlier LG-Sub guns required you to tip the water out before muzzle loading.

 

[tromic]

It does not help that there are no explanations about exactly how it works or more detail on the layout as having your customers figure it out may have them look elsewhere. As observed earlier it is not really covered by their patent which is washer vacuum seal based. In a way it is now a Mamba system, but with the improvement of the telescoping “”dynamic shutter” slider to get around the hydraulic lock which was a problem with the Mamba. Another Mamba system used today is the LG-Sub speargun, but it introduced the new “Black Head” muzzle update to create a muzzle body valve that eliminates hydraulic lock. That system uses an X-ring in the muzzle to slider seal interface. Earlier LG-Sub guns required you to tip the water out before muzzle loading.
View attachment 58209

I am still not sure how this x - ring work in LG Black head muzzle...

 

[popgun pete]

The only detail photo I have found is this one in the LG-Sub catalogue. You can see an X-ring sitting in the entrance of the alloy muzzle tube. The black plastic section carrying the short "light pipe" red sight rod and line wrap hooks is what LG-Sub call the ogive and is basically the nose cone. Because the tapered nose on the alloy tank forms part of what would be the nose cone on a cylindrical tank gun that means the front bulkhead is just that much smaller. Externally the alloy muzzle tube is a simple cylinder with two flats just behind the front screw thread so that the muzzle can be tightened up on the inner barrel tube. That front screw thread is what the plastic nose cap screws onto, this part being the "black head". This front cap has an entrance bore that is a close fit on the machined plastic line slides which are a form of Mamba sealed slider. When this front cap screws on it holds the X-ring in its seat in the front end of the alloy muzzle tube. There are 6 radial ports in the plastic nose cap that are at the back of the short troughs cut in the periphery of the cap which are to let water out when you push the slider in. It appears that the ring of 6 ports coincides with the front of the X-ring.

I have added some white lines to highlight where the tightening flat is on the alloy muzzle. When the front cap is screwed on it butts up against the front face of the ogive, which means the length of screw thread and the flats are swallowed up by the cap. As in all pneumatic guns using the inner barrel to hold the gun together the alloy muzzle holds the front bulkhead or ogive in place.

 

[tromic]

I had tried to draw some muzzle sketch about the function of X-ring in Black Head muzzle:

What vacuum muzzle guns are available off the shelf?

Sorry, I did download Claudio's video but only gave it a quick glance (in Italian with very few close up shots...).I might be able to get you some X-rings once I am back in China but can't find the exact size you are looking for. I think they are not a standard size. I don't know if the 14.8mm...

forums.deeperblue.com

But there was something missing, to be clear how it actually works...