Shock absorber

[tromic]

The viscosity of the fluid has a bearing on the result, using just the changing cross-sectional areas and mass of the fluid and the velocity is only part of the calculation. That is why shock absorbers use different viscosity oils to change their damping performance and that determines the degree of slowing of the mass flow rate in their pumping action. The fork oil we use in pneumatic guns comes in different grades for that reason. So the calculation of performance is not so straightforward as it was for a rubber sleeve damping unit.

Yes, that's right. Some testing should be necessary. Calculation results give just a boundary, first approximation, just an idea how to go.

 

[tromic]

I am going to renew an old Mares Mirage 70. My idea is to use 7 mm free shaft with hydro-mechanical shock absorber. This will be water barrel, not vacuum barrel, at least for beginning. I can easily switch to vacuum bared using regular shock absorber and closing water escaping holes with rubber tubing or band tape.
The screw on the top of muzzle would be replaced with TombaF700 screw (without sealing O-ring), just to have guidance for the shaft.



I believe hydro shock absorber would consume 6 J of piston energy, so the mechanical part of absorber would not have any work to do.

 

[tromic]

This is an attempt to capture with camera simple hydro damper. 1 kg (bottle of water and injection hydro-damper) falls from 0.5 m
Hydro damper is injection filled with water, which has 4 holes of 3.5 mm. Speed ​​on impact into the ground is 3.15 m/s Energy of 4.9 J.



http://www.youtube.com/watch?v=WlAjJJKUyFQ&feature=youtu.be

 

[tromic]

This might be hydro shock absorber for pneumo-vacuum speargun. An additional advantage would be that no water should be discharged from the gun before loading the spear.

 

[popgun pete]

Those 4 ports for water exit (not 4 + 4) were calculated based on 10 J. They would be smaller for 5 J.

It will be the other way around, smaller ports make the shock absorber harder to pump the water out of it, while larger ports make it easier. Basically the hydro shock absorber is reversing what muzzle relief ports in a wet barrel gun try to do, that is turn it into less of a water pump and not absorb energy from the shot. As a muzzle damper we want to absorb energy from the piston by pumping water through a restriction, so we create a small water pump in the muzzle.

 

[tromic]

It will be the other way around, smaller ports make the shock absorber harder to pump the water out of it, while larger ports make it easier. Basically the hydro shock absorber is reversing what muzzle relief ports in a wet barrel gun try to do, that is turn it into less of a water pump and not absorb energy from the shot. As a muzzle damper we want to absorb energy from the piston by pumping water through a restriction, so we create a small water pump in the muzzle.

Yes Pete!

Here is the simplest solution!? Just rubber tubing should be used over the muzzle ports. It acts like a valve when inserting the shaft and when water should be let out from hydro damper after the shoot.




This is how I did calculation of hydro-damper.

m (vode) - the mass of water.

 

[tromic]

I am going to make this for my Mirage 70. Free shaft 8 mm (TombaF800) with hydro damper. This should work either vaccum barrel or water barrel. Hydro shock absorber could be replaced to regular Mares shock absorber (same dimensions).

 

[tromic]

This could be a problem for all free shaft kits. This water, if left in a gun, has no where to get out. If water is not released from the gun before loading the shaft, after shooting damage to shock absorber and/or piston might occur.

 

[tromic]

This might be a way to make hydro damper for free shaft using muzzle without water escaping holes. I would probably combine hydro damper and common mechanical damper. I see a problem with design in case of aiming some angle up from horizontal line. In that case major of water would not be in desired position - in front of the piston, but around the pistons neck. In that case mechanical damper would be used.

 

[trromic]

Analysis of possible working of hydro damper for free shaft, phase by phase.
Muzzle mast be empty of water before inserting the shaft and the shaft should be inserted in muzzle above the water surface.

 

[trromic]

This version of hydro shock absorber for 7 mm free shaft would be easier to make.

 

[trromic]

This shock absorber might work even submerged in water. Two O-rings preserve some air necessary for proper operation.

 

[trromic]

This what might happen when water remain in sealed barrel.

 

[trromic]

Approximate calculation of hydro damper.
"Da" and "La" should be adjusted so kinetic energy of water from damper be little larger (30 %) than energy of piston. I take for "La" 8 - 12 mm.

 

[popgun pete]

Here is a sketch of the Doroganich hydro-brake muzzle system. It is not a scale drawing, so the diameters are slimmed down compared to the lengths in order to fit all the dimensions on the diagram. Hydrobraking occurs when the long piston nose enters the matching bore in the front of the muzzle as water is trapped in the muzzle section located immediately behind it which will be progressively squeezed out by the step on the front of the piston's tapered section advancing into it. Note that the hydrobraking section is situated after the ring of muzzle relief ports have been passed by the piston, so the trapped water there has to exit via the muzzle opening which is largely blocked off by the long piston nose moving through it. This flow restriction creates the hydrobraking action because the trapped water cannot escape at more than a certain rate governed by the clearances in the front end of the muzzle. The slight taper on the piston body may be to eliminate jamming while still having tight tolerances between piston and muzzle at full travel of the piston into the muzzle. Essentially the water itself is the muzzle shock absorber in this gun as it requires a pumping action to disperse it from the muzzle in the last 20 mm of piston travel.

 

[trromic]

Here is an another working solution from Russian forum:

 

[tromic]

This will be my new hydro damper for MirageTomba800HD. I had already tested hydro damper with same dimensions, but this should be even better.

 

[tromic]

I think about to make this damper for my Cyrano 1100 for 8 mm free shaft. I would use original Mares piston, just making a boring 8 mm instead of cone hole.
Or I will make it for 6,5 or 7 mm free shaft? Not sure yet. I already have TombaF800 adapter so there would be less work for 8 mm shaft.



Correction:
10.4 -> 10.7
10.65 -> 11

 

[sam mitchell]

Hi,

I'm jumping in on this thread a bit late. I've also been thinking of modifying the damper but for less sound.

Looking back on this thread post 17 gave an example of a piston (10g @ 30m/s) hitting the damper (4.5g) it stated the resultant speed would be 25m/s (I believe this was done using an energy ballance).

However when considering conservation of momentum you get a speed of 20.7m/s. Which leads to a drop in energy of 1.4J. I'm I right in thinking this is what is dissipated as sound? If so the only way I can see of reducing sound is to reduce the mass of the damper.

Does this line of thought seem correct?

Regards

Sam

 

[tromic]

Hi,

I'm jumping in on this thread a bit late. I've also been thinking of modifying the damper but for less sound.

Looking back on this thread post 17 gave an example of a piston (10g @ 30m/s) hitting the damper (4.5g) it stated the resultant speed would be 25m/s (I believe this was done using an energy ballance).

However when considering conservation of momentum you get a speed of 20.7m/s. Which leads to a drop in energy of 1.4J. I'm I right in thinking this is what is dissipated as sound? If so the only way I can see of reducing sound is to reduce the mass of the damper.

Does this line of thought seem correct?

Regards

Sam

Lower mass of the piston and damper would produce lower noise. Using vacuum barrel you'll also have lower noise than with water barrel. Using hydro damper there is also lower effective mass of the shock absorber (mainly the mass of the water that serves as damper).