Mares Mirage

[popgun pete]

One thing that I should point out is that the layout is slightly different on my gun, but much the same principle. The metal tube behind the brass piston is inside the tunnel in the plastic grip, but it is loose. As internal pressure inside the gun wants to blow the brass piston and thus the power selector rod backwards out of the gun it leans the back of the brass piston on the front metal tube. That in turn clamps what would otherwise be a floating "O" ring onto the second (hidden) metal tube directly behind it, that tube being a close fit inside the tunnel bore. That second metal tube presses on the second "O" ring located in turn behind it that seals on the step in the tunnel or bore running to the external environment from inside the plastic handle. Only the second metal tube is tight inside the tunnel in the plastic grip and everything works by having the metal tubes of exactly the right length. I will do a diagram and all will be made clear about why the early gun is so prone to leaking even after one has actually "fixed it". You do know already, but there is one particular aspect and it involves the "loose" front metal tube, the one right behind the brass piston.

 

[popgun pete]

Ah, interesting that they dropped the price that much. Pity it was such an uphill battle getting it to work.
Yeah, I sent the guy in question two of your pics. He really did not want to believe they existed and categorically denied it, haha. Dunno if he still thinks, it is not factory spec but a user mod.

Does seem that Mares reacted to it fairly soon as the V2 bulkhead is found in early red handles, too.

Thanks, as always, for elaborating.

The "red" handles may not all be early, the later parts list shows both rose (red) and white parts for the "current" layout, even though the diagrams are unchanged we know they are different guns because the "O" rings change both in number and type with respect to shore hardness. The coloured parts are otherwise identical, so Mares will have used up stock of red parts before or while using the white ones. Because I never thought the revised bulkhead was expanded rearwards I never noticed the front boss being truncated and the three quarter views don't show it and in the side profile views one's eye is drawn to your grip handle changes.

The low prices would be at cost, or even lower, just to clear the stock, note they were being shovelled out via a hardware store chain, not dive shops. At that time no local dive shops had stocked "Mirage" guns for months, maybe years, or at all, so they were quietly going out via the "back door", only no one was interested even at $50 which was cheap for any type of gun of the same length!

 

[popgun pete]

Here is the power regulator shaft sealing diagram. The reason the gun leaks after a period of non-use, say around a month, is that "O" rings tend to stick on a shaft if they sit in one position for any extended periods. You can feel this slight sticking whenever the power regulator knob is moved on any gun, but in the floating "O" ring "Mirage" that slight sticking action shifts the "O" ring off the gap between the regulator rod and the metal tube that it is pressing against and once it has moved it will not go back as if any air gets on the other side of the "O" ring then the pressure differential falls away. This is because the cross-section of the annular gap is so tiny that only very high pressure in the gun will resist this lift off of the "O" ring. Why does this not happen on other Mares guns, well the answer is the coil spring on the selector rod behind the brass piston that plugs the transfer port keeps a load on the pressure seal "O" ring if it is not otherwise mechanically held, even with no pressure in those guns. No space in the "Mirage" for a coil spring in the early gun, or the later one for that matter, so the "Mirage" could turn itself into a leaker if the pressure sealing "O" ring had slightly stuck on the selector rod shaft. But get the selector rod moving without the sealing action being lost and your "Mirage" was ready for action. So the "performance mirage", now you had a working gun and now you did not, was down to this very poorly held "O" ring. Use your gun every day and you probably never had a problem, as long as the Mares production line workers had installed all the "O" rings in the correct locations without damaging any of them.

 

[popgun pete]

Seeing as someone recently asked here are the two versions of the later Mirage diagrams, note the diagram part numbers change. Note plastic pistons are used in the lower diagram.

Mares never adjusted the diagram to show the change to the front of the grip handle when the new regulator bulkhead was used so I changed it myself. The front boss on the grip handle was shortened to allow a thicker regulator bulkhead being used and Mares got rid of the cutout and "keyhole" seen in the original version (see diagram inset).

Note that power regulator shaft sealing is now similar to that used in other Mares models, except there is still no coil spring behind the piston plug part no. 37.

 

[popgun pete]

And here is the diagram for the gun as it originally appeared.

Note that the very earliest guns have a metal piston with three rubber seals, two cup seals facing either way with a central "O" ring. Then they use a plastic guide collar that replaces the front rubber cup seal on the metal piston (as shown above). Things go downhill after that as the gun gets equipped with plastic pistons, including the smaller diameter tailless pumping barrel piston. Early guns also don't have the bump on the top section of the pivoting lever in the grip handle, it was added so you could flick the lever out by pressing at the top rather than pulling it out from the bottom, anyone who has ever loaded a Mirage in the water on a surgy day will immediately know why that was done!

 

[popgun pete]

Mares often sell spare components as a complete set and I noticed that the complete rear handle was listed as two different sets with different part numbers, the second set being for the Mirage 100. Looking through the list of components in each set shows that they are exactly the same, so I suspect the difference is the Mirage 100 has the white plastic parts and the smaller original gun has the red plastic parts. On the parts list these coloured items have the same diagram number but a different Mares part number. The only exception is the rear inlet valve cap which is black on the shorter gun and white on the Mirage 100, but they also have different part numbers.

 

[popgun pete]

Thought that I would add this here if anyone wants to understand how the "Mirage" works.

Although the Mares “Mirage” pneumatic speargun uses the principle of loading via a smaller ID inner barrel of 10 mm, and shooting from another larger ID
inner barrel of 13 mm, that is not strictly speaking how it operates. The hydropneumatic auxiliary hydropump spearguns do work that way, e.g. Aquatech “Black Sea”, Alcedo “Hydra” and “Hydra Sprint”, because the spear can be inserted without pushing any resistive medium behind it when the spear is moved to the rear of the gun’s main barrel, ready for shooting, as the gun’s interior can be bypassed by a water valve being left open to the environment.

How the "Mirage" works is that it progressively shifts air from the partitioned off rear section of the gun by using the 10 mm diameter pumping barrel and transfers that air into the front tank, the gun being split into two sections by the partitioning bulkhead located between the large volume and nearly full length front tank, Vft, and the balance of the gun. The rear section is a combination of the volumes of the pumping barrel Vpb, the main barrel Vmb and the pre-chamber Vpc at the rear of the gun. The pumping barrel operates as a gas molecules shuttle as the proportion of gas being shuttled across is the same each time, but the amount differs as for each pumping barrel stroke there is less gas being left in the rear end of the gun. After each pumping barrel stroke is completed the pump refills from the main barrel and pre-chamber which are always connected, but each time that refill pressure is lower, hence less gas molecules are transferred as the number of pumping barrel strokes increases. The pumping barrel has a very high compression ratio, so it can squeeze even small gas quantities down to a pressure which can move across into the front tank. The pumping barrel stroke is shorter than the main barrel stroke, or working course of the piston, because the former terminates at the partitioning bulkhead, whereas the main barrel piston travels further back to latch on the sear lever's tooth which pivots inside the main barrel tube.

The proportion of gas transferred by the pumping barrel is given by Vpb/(Vpb + Vmb + Vpc) which will be denoted here by K, which is a ratio or a percentage.

Therefore K = Vpb/(Vpb + Vmb + Vpc)

K can be calculated by measuring the respective gun internal volumes, but it can also be obtained from the original version of the “Mirage” speargun's pressure reduction table by using the first pumping barrel stroke result where the numbers are larger. (Mares kept using this table without recalculating it for the longer guns and those with a well type bulkhead, which increases Vpc, in place of the original flat face bulkhead). As the initial start pressure is 30 Bar and the pumping barrel stroke has reduced the rear section’s pressure to 22 Bar by removing 8 Bar, then K must equal 8/30 or 0.266666 repeating. The first pumping barrel stroke leaves the rear section with (1 – K) gas molecules (note proportions are being used here, not the absolute values), the second stroke with (1 – K)^2 gas molecules, the third stroke with (1 – K)^3 gas molecules and so on. As the pumping barrel refills by gas travelling through a ball type inlet valve, at a certain pressure the ball valve’s biasing coil spring will start to shut off the gas flow, hence the calculations will be slightly out at very low pressures, but by then the effort required to push the pumping barrel piston back will be minimal given the small cross-section of the pumping barrel and its piston.

Using the value of 0.26666 for K the values for (1 – K)^n for values of n from 1 to 5 have been calculated and the results shown below. Note that Mares probably rounded the results shown in their own table, hence the value of K may be slightly different and reverse calculating it, as I have done here, may introduce some mathematical error.

Pumping barrel stroke 1 - 0.7333; stroke 2 - 0.5378; stroke 3 - 0.3944; stroke 4 – 0.2892; stroke 5 - 0.2121.
If we multiply the above numbers by 30 Bar then we should obtain the numbers shown in the “Mirage” pumping barrel table.
Pumping barrel stroke 1 – 21.99 Bar; stroke 2 – 16.13 Bar; stroke 3 – 11.83 Bar; stroke 4 – 8.68 Bar; stroke 5 – 6.36 Bar.
If we multiply those same numbers by 40 Bar then we obtain the numbers for a “Mirage” speargun operated at 40 Bar.
Pumping barrel stroke 1 – 29.33 Bar; stroke 2 – 21.51 Bar; stroke 3 – 15.78 Bar; stroke 4 – 11.57 Bar; stroke 5 – 8.48 Bar.

As the pressure in the rear of the gun is progressively decreased by using the pumping barrel as a "gas molecules" transport shuttle, the pressure in the front tank goes up, in fact it will be pushed higher than the gun's "cocked to shoot" pressure. When the power selector switch is subsequently moved back to the "full power" shot position the front tank can refill the rest of the gun's internal volumes and the pressures throughout the gun then equalize.

Note that longer “Mirage” type guns will have different values for K, as while the main barrel and pumping barrel volumes will increase with their additional barrel lengths, the volume of the pre-chamber, Vpc, will remain the same if they all use the well type bulkhead as distinct from the flat bulkhead used originally. For a super version “Mirage Evo” with a 14 mm diameter main barrel the value of K will be smaller as Vmb will be larger and K is inversely proportional to Vmb (refer to above mathematical expression for K).

 

[popgun pete]

Operating the Mirage pumping barrel using the spear shaft as a push rod for the built-in pump. Note that the tang or shaft stop diameter on an 8 mm spear is 9 mm, which is why the pumping barrel bore is 10 mm to provide the minimum clearance. The sliding stop ring on the shaft locates in a slot under the muzzle, but in practice the stop ring tends to move along the muzzle tearing up the anodizing and will not stay put in the slot while you are pumping. Mares at one time used thin stop rings which tended to tilt on the shaft and act as a brake ripping up the shaft surface, so watch out when pumping these guns!

 

[popgun pete]

Note that in the Sten spearguns all the power regulators have a coil spring located directly behind the power regulator piston. The purpose of this spring is to help reduce the operating effort in using the power regulator because while high air pressure in the gun is trying to blow the shaft backwards in the gun this is partly offset by the spring tension opposing it. The other job of this coil spring is to apply a load to the retaining bush that holds the sealing “O" ring on the regulator shaft in position in its recess fronting the narrow tunnel that runs back through to the power regulator gate in the handle’s left hand side. Now because the power regulator piston has no open space to travel back and forth in, unlike the other Mares guns, the Mirage has no coil spring. That means there is no clamping effect on the power regulator shaft sealing "O" ring and it is only gun internal pressure that holds it back. Due to the small size of the "O" ring and the not so small diameter of the tunnel behind it the area that pressure is exerted against is low and any stickiness of the “O” ring on the shaft may overcome the force being applied and it can then lose its contact with the seating area that it should be pressed against. That is why early Mirage guns leak at this location as there is really nothing there to hold the seal in place. The revised guns have a very different arrangement with a disc spring (a flat conical washer) which is only effective when the piston is retracted in addition to a retaining plug in red plastic and another backing ring. While not as good as a coil spring it is better than nothing and the red plug can stop movement unlike the early metal sleeve that was not held by anything, any sealing effect totally relying on gun pressure.

 

[tromic]

Note that in the Sten spearguns all the power regulators have a coil spring located directly behind the power regulator piston. The purpose of this spring is to help reduce the operating effort in using the power regulator because while high air pressure in the gun is trying to blow the shaft backwards in the gun this is partly offset by the spring tension opposing it. The other job of this coil spring is to apply a load to the retaining bush that holds the sealing “O" ring on the regulator shaft in position in its recess fronting the narrow tunnel that runs back through to the power regulator gate in the handle’s left hand side. Now because the power regulator piston has no open space to travel back and forth in, unlike the other Mares guns, the Mirage has no coil spring. That means there is no clamping effect on the power regulator shaft sealing "O" ring and it is only gun internal pressure that holds it back. Due to the small size of the "O" ring and the not so small diameter of the tunnel behind it the area that pressure is exerted against is low and any stickiness of the “O” ring on the shaft may overcome the force being applied and it can then lose its contact with the seating area that it should be pressed against. That is why early Mirage guns leak at this location as there is really nothing there to hold the seal in place. The revised guns have a very different arrangement with a disc spring (a flat conical washer) which is only effective when the piston is retracted in addition to a retaining plug in red plastic and another backing ring. While not as good as a coil spring it is better than nothing and the red plug can stop movement unlike the early metal sleeve that was not held by anything, any sealing effect totally relying on gun pressure.
View attachment 57835

anello parback ? - This is back-up (parbak) 90 durometer ring...

8. Parbak Back up rings

Buy 8. Parbak - Back up rings online at O-RING-LAGER webshop

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[popgun pete]

anello parback ? - This is back-up (parbak) 90 durometer ring...

8. Parbak Back up rings

Buy 8. Parbak - Back up rings online at O-RING-LAGER webshop

www.o-ring-stocks.com

Thanks, I looked through various translation possibilities but never found that one. Do you know if it is a seal or just a support? If the "O" ring sitting in front seals on its inner and outer periphery then no need to seal on its rear side. Usually "O" rings in this application seal on their inside (to the shaft) and on their backs against the step they sit on as the diameters change where the shaft access tunnel opens out to their circular seat.

On reading the article the back-up ring seems to serve to stop the "O" ring from extruding down the low pressure bore of the regulator shaft operating tunnel, hence in itself it is not a seal. When I first opened my Mirage up I found two "O" rings at the rear of the innermost (when looking from inside) metal sleeve and none between them, so it was obvious why it was leaking. When I spoke to the woman at Airdive where I purchased my one and only Mirage repair kit and asked about this she said that it was probably wrongly assembled as it was not unusual to find such mistakes in the Mirage guns which they repaired. I had wondered if the pressure had forced one ring backwards to travel down the second sleeve which is not intended to be removed as you have to dig it out, but subsequent rings put in the correct position never moved around as such, however I never thought about them extruding under high pressure loading. When my Mirage worked it never leaked, it only failed while sitting unused for a lengthy period rather than out on a dive. The two regulator shaft rings I removed were squashed together alongside each other and in a pinched up on one side configuration, so I believe that is how they were installed at the factory. QA checking must have been zero!

 

[popgun pete]

A few morsels of information here and mention of who designed the Mirage gun. I searched for a patent on it some years ago, but nothing showed up. Possibly it has not been added to the on-line patent databases which are most widely accessible.

Pesca Sub Blog

Blog Pesca Subacquea e Apnea

www.pescasublog.it

 

[popgun pete]

It has just occurred to me that the second "O" ring shown here may not be necessary. I just replaced it thinking the sleeve had to be sealed into the grip handle tunnel, but never checked if the middle “O” ring served to seal both on its inner and outer peripheries simultaneously. As a ring was there, in fact there were two, I just assumed that one ring needed to there. Anyone else find a second ring behind this inner sleeve? Leaving it out allows the piston to retract back a tiny bit further by the thickness of that ring as it sits when retracted on the two sleeve lengths plus the ring width sitting between them.

 

[tromic]

My Mirage was the early model, as it originally appeared.

Here is a drawing and the dimensions of the parts.

I was not sure about dimensions of the sealing O-ring so I did calculation for two sizes: 3.68 x 1.78 and 4 x 2 mm.
I choose to use 4 x 2 mm. I had only one O-ring.

 

[popgun pete]

What I am asking is was there a second "O" ring behind the second sleeve, or have you never pulled it out? I had to make a thin rod with a tiny right angle bent tip (hot forged) to slide down the innermost sleeve and pull it out. Along with the sleeve came the two "O" rings, although I think that there should have been only one, or perhaps even none. The rings dragged out were already distorted, so they were going to be thrown out anyway despite being nicked by the hook on the thin rod during the extraction. I don’t have that rod anymore as I thought that I would never need to use it again.

The second sleeve was about the same size, but of a slightly different colour and not the twin of the first, so I could easily tell them apart and not mix them up. That second sleeve is still in the handle as I pressed it back in with a new seal behind it where it only functions as a gasket. This is because the join in the regulator shaft passes through it.

 

[popgun pete]

A quick comparison shows your gun is different to mine and from memory you have the bump on the top of the folding lever which is absent on my gun as they had yet to change the mould. Many parts are still the same, but even then they were making changes.

 

[tromic]

What do you think about possibility of this arrangement?

 

[popgun pete]

What do you think about possibility of this arrangement?
View attachment 57850

That might stop the "O" ring extruding, but it is the other side that needs changing to better imprison the "O" ring. We can see from the later changes that is where Mares applied their modifications. They already knew this was the way to go because the first Sten in 1967 has a brass collar holding the power regulator shaft "O" ring in place and that was held back in turn by the coil spring located in front of it to press the collar into the plastic handle moulding's front boss. Later on the brass collar was replaced by a plastic version, but the principle was still the same.

 

[popgun pete]

I think the Mirage was originally conceived as a gun with the longest possible pumping barrel and with the partition needed to create the smallest volume to be pumped down being located as far rearwards as possible in the gun. That requires any bulkhead to sit just in front of where the sear lever catches the main barrel piston. This bulkhead just needed to be flat and the cursor or power regulator then pushed further back in the gun to sit behind it compared to the layout in the Stens. This gun would require a simple dogleg selector gate like the Sten, but forward and down would be pumping barrel loading and up and back would be full power shooting. There would be no power selection, the gun was solely to be a high power shooter.

What I think happened next was someone decided to make the Mirage multi-power and for that they needed longer travel in the selector gate, so the regulator system had to be pushed forwards slightly and the big bore tunnel that was to swallow the piston plug completely in the handle body was no longer necessary, even though it was still there, so they cobbled an arrangement together to make the changes work and modified their prototype. The line retaining passive clip on the trigger finger guard which was probably a stop gap idea ended up being incorporated in the gun for production to get it on the market quickly.

 

[popgun pete]

The Sten appeared before the Mirage, so possibly the latter started by rejigging the parts to create the new gun out of the components used in the Sten by eliminating the power regulator chamber and pushing all the parts associated with it rearwards in the gun, including the power regulator which was now an incremental load or shoot selector switch. That would cramp up the parts in the former power regulator unless something was left out, although initially the power regulator access tunnel was made large in diameter to accommodate everything.