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Shock absorber

popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
4,536
1,288
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I don't think the shaft tail adapters would be giving these problems, it is probably just extensive use and maybe using high pressure in the guns. I think these pistons are moulded in acetal or POM, which is the same thing. Delrin is another engineering plastic that can be used, but you don’t often see it in production guns.
 
popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
4,536
1,288
353
A culprit may be the bumps on the front of the Airbalete piston. Mares introduced a circle of bumps on their piston nose which when the piston leans on the shock absorber places the ring inside the bore hole in the anvil face. On Omer guns this ring of bumps sits on the anvil face and localises the impacts rather than evenly distribute them. I think I have mentioned this before when looking at the Omer XII which shares some parts with the Airbalete.
Airbalete piston

Just checked: https://forums.deeperblue.com/threads/omer-quitting-pneumatic-spearguns.116908/page-4
 
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tromic

Well-Known Member
Aug 13, 2007
1,722
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Hi everyone. I know the topic and the discussion is a little bit old. But I could not find some details on shock absorbers suitable for Omer Airbalete. Mine seems to be damaged and piston gets stuck after each shot. I am planning to build a new one on my mini lathe. Which material should I use? Polyamide? Or POM? Or castermid?
I would make a try to convert Airbalete to Free Shaft Hydro Damper version.
I did a similar project with my Cyrano and it worked well.


I do not know the exact dimensions of Airbalete muzzle but here is an idea for 11 mm barrel and 6.75 mm spear.
I am not sure about OD of the piston, it might be 10.7 mm?
The front POM part is not necessary for at least testing the operation... Its ID is not critical, it could be 7 mm.
Other dimensions must be precise!

1663433614688
 

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tromic

Well-Known Member
Aug 13, 2007
1,722
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I would make a try to convert Airbalete to Free Shaft Hydro Damper version.
I did a similar project with my Cyrano and it worked well.


I do not know the exact dimensions of Airbalete muzzle but here is an idea for 11 mm barrel and 6.75 mm spear.
I am not sure about OD of the piston, it might be 10.7 mm?
The front POM part is not necessary for at least testing the operation... Its ID is not critical, it could be 7 mm.
Other dimensions must be precise!

View attachment 58180
I suppose the life of the piston and shock absorber would be much longer than in usual designs because there is no direct impact with high kinetic energy. I know some guys who prefer water barrel over vacuum barrel spear guns because of higher reliability, There is no sealing cuff/O-ring for vacuum and the spear is without the tang, line slide.. The only downside is the necessity to front tie the mono or Dyneema to the shaft. I personally do not like that but there are a lot guys especially among Spanish who use "free shaft" from the time the famous Ramon (Karayo) made his tovarich kit.
Just to remind, the advantage of vacuum barrel over water barrel is, according to my measurements, 12% to18% in energy or 5.8 % to 8.6% in speed.
What mainly effects the speed of the shaft is the thickness of the line connected to the shaft and hydrodynamic properties of the shaft with its components.
In free shaft configuration the best results are when the line is attached to the shaft without using any kind of micro slider.
 
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tromic

Well-Known Member
Aug 13, 2007
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.Right, Pete! It is additional about 2 J (my estimation). So the force might be about 110 kg instead o 86 kg, or 220 kg in case of 4 mm breaking distance. If some water would be trapped in a muzzle (broken vacuum system) it is clear that under such a high pressure some water would be injected behind the piston into the barrel!


This is how mares shock absorber works in asso muzzle. I made measurement using a vice and a dynamometer, so it is not very precise but might be interesting. 5 mm of compressing of shock absorber requires close to 1400 kg. If measured with normal measuring equipment the result would be less, but that would be a big value too!


I have just read through this topic again and noticed a mistake about my estimation of energy necessary to jerk the spear free of the piston.
2 J was too much, but that energy is actually not necessary for the calculation because if the force to jerk the piston free of the piston would be even 10 kgf that would be neglectable compared to forces more interesting for estimation. Here is a diagram of forces we deal with when speaking about shock absorber. This diagram is from measured and calculated data for Mares shock absorber for my Cyrano 850 spear gun.
At 30 m/s the energy of the piston (16g) is about 7.2 J. To slow down that piston the shock absorber would be compressed for about 3.5 mm.
The force to the piston and shock absorber is gradually being increased up to the pick value of 738 kgf, after that being drop down. After the shoot and returning to steady state the force to the piston and the shock absorber would return to 30 kgf, in this case (depending on the pressure in the speargun).

In another example for Cyrano 1100 on 30.5 Bar, if the piston would be 16 g, and the spear 361 g the speed of the piston on impact with shock absorber would be 40 m/s. Cyrano shock absorber would be compressed for 4.1 mm and the peek force would be 1198 kgf. Energy delivered to the shock absorber would be 12.8 J.

1663325827008
 
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tromic

Well-Known Member
Aug 13, 2007
1,722
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Here is a few images of my old project regarding Mirage hydro damper for 8 mm shaft with Tomba cone ring, and slider.
It worked as water barrel or vacuum barrel depending on if I used the rubber tubing over water escape ports or not.
Part of the water that moves forward gives some initial speed to the cone ring and the slider so it diminishes the impact to the cone ring too.
Kinetic energy of the piston was 4.9 J and the kinetic energy of water escaping shock absorber 5.2 J

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tromic

Well-Known Member
Aug 13, 2007
1,722
216
153
Here is a few images of my old project regarding Mirage hydro damper for 8 mm shaft with Tomba cone ring, and slider.
It worked as water barrel or vacuum barrel depending on if I used the rubber tubing over water escape ports or not.
Part of the water that moves forward gives some initial speed to the cone ring and the slider so it diminishes the impact to the cone ring too.
Kinetic energy of the piston was 4.9 J and the kinetic energy of water escaping shock absorber 5.2 J

View attachment 58214
Additional information regarding the sketch above.
Average braking force applied to the piston was 616 N. This is from the formula where the Work = force F * distance.
What is more interesting is the average pressure of the water compressed by the piston is 120 bar. The peak pressure might be still higher, maybe 2 x..? Remember that the pressure in the speargun was 30 bar. This over pressure is the cause of water being injected behind the piston making the oil in the speargun milky.
 
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