DEMYSTIFYING " What is COBRA valve tech ? "

[oldpro]

 Actually Scott it’s almost the exact opposite of your statement in my testing. The smaller chamber has more effect closing the valve due to less air volume inside the chamber so less air volume means quicker direction change of the poppet from opens to closing its like a air shock the larger the piston the slower and softer the rebound. Short stiff shocks or long soft shocks that’s what we’re talking about here, I am however interested in the data you have that supports your testing maybe I’ve missed something important. Always something new to learn.

[Motorhead]

In this equation is how jetted / vented .... Not an exact science by a long shot !!
We can agree to disagree on the subject of chamber sizing, but can agree either way you go if you are paying attention to cause & effect some pretty impressive results can be achieved.
My latest & link above is a rather large chamber on quite small venting FWIW

Scott

[PikeP]

Huh, never using this valves tech I'll give my impression of it, as I certainly do not intend to steer anyone wrong feel free to correct me.

Pressure differential inside chamber is determined by initial pressure, volume and vent size or 'leak rate'.

Larger vent / leak = larger pressure differential
Smaller vent / leak = lower pressure differential (pressure in chamber remains closer to initial)

Smaller chamber = larger pressure differential
Larger chamber = lower pressure differential (pressure in chamber remains closer to initial)

You also have to consider the potential "pressure shock" the chamber sees upon initial strike of the hammer where the distance the poppet travels and the pressure rise it would cause in a closed chamber MAY exceed the leak rate inside the chamber, meaning you're compressing air even if ever so minutely for a fraction of a millisecond...(small enough chambers and vents will see this phenomenon IMO)

These valves have lots of room for arrangement, and what works best for a 20 fpe gun may not for a 200 fpe gun, or maybe it does, I wouldn't know but its good to ponder such questions...

Nearly most any airgun may see benefit with these types of valves, but where they truly shine is in air guns with high pressure drops in the plenum during the shot cycle, as this helps maintain a higher pressure behind the poppet as to reduce the chance for a second or third opening which is ever so more likely as you have higher pressure drops within a valve, or in cases where there's little force holding the valve closed to begin with (ie: low pressure operating guns, or extremely balanced valves, both being very prone to hammer bounce). Any benefits beyond that are outside of my current realm of understanding.

[oldpro]

In this equation is how jetted / vented .... Not an exact science by a long shot !!
We can agree to disagree on the subject of chamber sizing, but can agree either way you go if you are paying attention to cause & effect some pretty impressive results can be achieved.
My latest & link above is a rather large chamber on quite small venting FWIW

Scott

The venting will definitely have the greatest effect regardless of chamber size. I found that chamber size mattered very little because it could be tuned by the venting quite easily

[AlanMcD]

Travis,

Since you are active in this thread, several of us have been trying to find out the correct or-ring (size/material/hardness) used in the chamber in the JSAR SS2 valve.  Scott said you would know.  Can you please let us know? Thanks!

[Motorhead]

Being this thread is likely to live for many years .... wish to elaborate a bit on the disagreements in chamber size and how this effects the tune.

These numbers will be that of a sample only so one can easily follow / understand whats going on ( As i see it )

So lets say our poppet sitting over the valves throat is .350" in diameter and the stem length hammer can strike sticks out .125" .. so the max lift obtained is no greater than .125"
And for sake of simple design the o-ring for chamber in contained within the poppet head and the tube Cobra tube attached to intake end of valve such as 1st picture.

IF the chambers volume is kept small and the vent hole small ..... As poppet is lifted off the seat the air space within the chamber creates COMPRESSION and higher the poppet is pushed within chamber GREATER will be the opening resistance. It acts very progressive in that harder you strike the valve driving it towards more lift, more it resists !  Valve will indeed exhibit a short dwell tendency.   Because the vent is small, the contained air is slow to bleed off and this compression rise is exaggerated.
* If the venting was made larger while using a small chamber volume it would result in less effort required to open and keep the valve open while ALSO having the lower volume tube more quickly equalize / collapse to the surrounding pressure drop within the valve/plenum.

Next example is we have the chamber LARGER with a small vent .... As poppet is lifted off the seat there is LESS compression happening simply because the Stroke has remained the same, but chamber volume is greater so in simple terms a lower compression ratio.  The valves resistance to lift becomes far less progressive and Does Not increase in opening resistance as sharply as a smaller volume does.
Being vented small it contains nearly the same pressure within tube from where it started before the shot cycle & the retained pressure has increased the ability to push the poppet closed.
* IF the venting is made larger while using the larger chamber volume the opening forces would still be low and the closing effect would be of a tad longer dwell.


These two examples really in my experience shape the picture of how the system works. They are in application if looked at in extremes of each example ... Majorly different in the way valve will operate requiring pretty drastic changes it hammer mass, spring energy to get EITHER to make the same power.  Or in a tuners sense, each extreme or middle ground becomes what one uses based upon the guns hammer weight, spring in use, caliber and power, tuning flexibility wanted.


JMO,
Scott S

[mobilehomer]

The question remains - when will a Cobra valve for a mid-power .22 be available for those of us that do not have access to machine shop tools?

[Motorhead]

The question remains - when will a Cobra valve for a mid-power .22 be available for those of us that do not have access to machine shop tools?

 Likely not .... The man behind the tech and getting them and other valve designs made for the masses has stepped away from such endeavors as i see it.

[mackeral5]

I'm willing to be a Cobra conversion could be had as a component of a FULL TUNE service, from a certain tuner located in the NW...

[PikeP]

Thanks for all your contributions into the cobra valves and their evolution Scott. Your observations line up well with my theories and thoughts.

I'd love to see a version ran with just the tolerance between chamber and poppet being its only 'vent', which with some ingenuity could be expanded in a way that is adjustable, thus eliminating a need for a seal. Say an inner poppet stem that opens a 'disc' at the opposing end of the poppet that either increases or reduces the tolerance between poppet and chamber. Which would make it externally adjustable with the only need to remove hammer to access adjustment opposed to requiring degas/valve removal.

[Motorhead]

I'm willing to be a Cobra conversion could be had as a component of a FULL TUNE service, from a certain tuner located in the NW...

Lol ... It has happened 

[mackeral5]

here are a few Cobra transplants.....All have very light hammers and pretty good efficiency numbers.  I gravitate towards Scott's theories around ultralight hammers, and barely-there OD peek poppets....I add my own twist of reducing stem diameter vs. increasing throat diameter where possible, working towards one of Bob Sterne's targets of valve throat area =  valve exhaust area + 10%.

QB78/Gauntlet





Edgun R3



P15





Bulldog







Note the lack of adjustable jetting in the Bulldog.....  that was my most recent conversion.  I won't use jets going forward, no need to adjust once set up properly.  Start small, go larger until desired effect achieved---once you have a nice snappy shot cycle you are very close.  Start running strings and calculating efficency....

Note as Matt described Cobra valves shining in regulated applications with extreme pressure drop, these are all in regulated guns with roughly .5-.75cc plenum.....

Also note, no machine shop required....  They are not pretty, but they are fully functional and could be easily replicated using my crude, or someone else's advanced fabrication methods....