DEMYSTIFYING " What is COBRA valve tech ? "

[skorec]

Thinking this thread & subject has been buried long enough .... Shameless bump to get the info out there to a new audience.

I dont think people quite understand whats taking place in the thimble or understand how it helps. Might need to make a video or something.

YES - Some principle video/animation may help for sure because understanding in alien language is not easy .

Cracking/opening force at  standard valve depend of area on which HPA is pressing/pushing.  Reducing this area  at SS balanced valve is make via creating  zero/atmospheric pressure on part of it.
 
At cobra valve it is make probably via creating the same HPA pressing/pushing from opposite side ?  - which way?

[mackeral5]

Today I found the missing oring which allowed me to finish my spare P15 tube.  This one is equipped with an extended plenum, which yields 25cc plenum of regulated air and 195cc of high pressure air, 220cc total.  I made a 2" long .25" in diameter cobra chamber.  The poppet extends approximately .25" into the cobra chamber.  A threaded plug extends approximately 1/8" into the top, leaving an open chamber of approximately 1.625"  I guessed at jetting and started with a .055 jet.  My reasoning for the larger jet was the larger cobra chamber should have a greater affect on the poppet.  The reg is set around 1900psi I believe. 

After degassing and switching tubes I ran some tests to dial in HST for 850ish FPS. 

Previously (non-cobra) the best I could do with the extended plenum and a >40fpe tune was 26 shots averaging 855fps with JSB Redesigned Monster 25gr.  Granted I didn't spend much time, but I did try a few different reg/hst settings and the above numbers were representative of non-cobra results. 

With the added cobra chamber there is a significant improvement.  45 shots averaging 856fps.  This is without an SSG, so I'm sure there is a little more room for improvement.   

Note ES is rather high, I have a Huma reg on order that will hopefully help in the ES department. 

Here is a chart:

[oldpro]

Today I found the missing oring which allowed me to finish my spare P15 tube.  This one is equipped with an extended plenum, which yields 25cc plenum of regulated air and 195cc of high pressure air, 220cc total.  I made a 2" long .25" in diameter cobra chamber.  The poppet extends approximately .25" into the cobra chamber.  A threaded plug extends approximately 1/8" into the top, leaving an open chamber of approximately 1.625"  I guessed at jetting and started with a .055 jet.  My reasoning for the larger jet was the larger cobra chamber should have a greater affect on the poppet.  The reg is set around 1900psi I believe. 

After degassing and switching tubes I ran some tests to dial in HST for 850ish FPS. 

Previously (non-cobra) the best I could do with the extended plenum and a >40fpe tune was 26 shots averaging 855fps with JSB Redesigned Monster 25gr.  Granted I didn't spend much time, but I did try a few different reg/hst settings and the above numbers were representative of non-cobra results. 

With the added cobra chamber there is a significant improvement.  45 shots averaging 856fps.  This is without an SSG, so I'm sure there is a little more room for improvement.   

Note ES is rather high, I have a Huma reg on order that will hopefully help in the ES department. 

Here is a chart:

Huge improvement!

[Rallyshark]

Today I found the missing oring which allowed me to finish my spare P15 tube.  This one is equipped with an extended plenum, which yields 25cc plenum of regulated air and 195cc of high pressure air, 220cc total.  I made a 2" long .25" in diameter cobra chamber.  The poppet extends approximately .25" into the cobra chamber.  A threaded plug extends approximately 1/8" into the top, leaving an open chamber of approximately 1.625"  I guessed at jetting and started with a .055 jet.  My reasoning for the larger jet was the larger cobra chamber should have a greater affect on the poppet.  The reg is set around 1900psi I believe. 

After degassing and switching tubes I ran some tests to dial in HST for 850ish FPS. 

Previously (non-cobra) the best I could do with the extended plenum and a >40fpe tune was 26 shots averaging 855fps with JSB Redesigned Monster 25gr.  Granted I didn't spend much time, but I did try a few different reg/hst settings and the above numbers were representative of non-cobra results. 

With the added cobra chamber there is a significant improvement.  45 shots averaging 856fps.  This is without an SSG, so I'm sure there is a little more room for improvement.   

Note ES is rather high, I have a Huma reg on order that will hopefully help in the ES department. 

Here is a chart:

WOW!  That is an awesome improvement there, and I bet you're right about that ES.  The Huma should help with that.  Great job!!

[mackeral5]

I tried adding the SSG back into the mix and I actually lost efficiency.  I'm thinking with hammer free flight the cobra chamber needs a larger jet.  with no hammer spring preload against the valve the cobra effect is so great that it is requiring excessive hammer strike to achieve the desired velocity and in turn this is causing excessive dwell before the valve slams shut.  that's just a hypothesis...

[oldpro]

I tried adding the SSG back into the mix and I actually lost efficiency.  I'm thinking with hammer free flight the cobra chamber needs a larger jet.  with no hammer spring preload against the valve the cobra effect is so great that it is requiring excessive hammer strike to achieve the desired velocity and in turn this is causing excessive dwell before the valve slams shut.  that's just a hypothesis...

I run mine with no ssg or tss its plenty efficient without any extra help that robs power BUT if i was in a competition wanting every extra es% I would run a ssg.

[Motorhead]

I tried adding the SSG back into the mix and I actually lost efficiency.  I'm thinking with hammer free flight the cobra chamber needs a larger jet.  with no hammer spring preload against the valve the cobra effect is so great that it is requiring excessive hammer strike to achieve the desired velocity and in turn this is causing excessive dwell before the valve slams shut.  that's just a hypothesis...

I run mine with no ssg or tss its plenty efficient without any extra help that robs power BUT if i was in a competition wanting every extra es% I would run a ssg.

No further comment  ... 

[mackeral5]

I tried adding the SSG back into the mix and I actually lost efficiency.  I'm thinking with hammer free flight the cobra chamber needs a larger jet.  with no hammer spring preload against the valve the cobra effect is so great that it is requiring excessive hammer strike to achieve the desired velocity and in turn this is causing excessive dwell before the valve slams shut.  that's just a hypothesis...

I run mine with no ssg or tss its plenty efficient without any extra help that robs power BUT if i was in a competition wanting every extra es% I would run a ssg.

No further comment  ... 

Thanks guys, again.  That makes life easier.   With a .25" OD poppet and no ssg  cocking is buttery smooth even over 40 fpe.....

[mackeral5]

Over on another thread I posted my intentions to test my .22 P15 unregulated with Cobra and without.  Scott predicted the results would not be favorable, and surprise, he was correct. 

Based on the expectation of unfavorable results I decided to quickly test at max preload and compare the cobra and non-cobra numbers.  I only filled to 3k for each test.  JSB Redesigned Monster 25gr pellets.

The unregulated, cobra string went like this:  899 to 997  on shot 7 then down to 870 on shot 25.  127fps ES, lol.. 

Then I removed the jet from the cobra chamber and also removed the oring from the poppet, effectively disabling the cobra chamber.  Refilled to 3k and took a shot...

1033fps!!!!!!  took another shot  1024fps!!!  remember, the first shot of the cobra equipped string was only 899fps.  The cobra chamber has major influence on the poppet.   

I dialed hst down to around 900fps and shot a non-cobra, unregulated string.  This string went 905 up to 995 on shot 6 and back down to 881 on shot 25.  25 shots averaging 937fps with an ES of 118, lol.

Scott predicted the Cobra chamber would result in greater ES than non-cobra and he was correct.  Sometimes I have to see things with my own eyes, this was one of those times.....

[mann]

I was having same problem with my war Cobra valve and SS valve . I was able to make smaller transfer ports to bring the es down to 20 fps but I also had to use more preload to get the same power while running unregulated

[mann]

It's still More efficient than running stock valve  unregulated once your able to get the es down 

[mackeral5]

It's still More efficient than running stock valve  unregulated once your able to get the es down

Understood,   I've been following your threads.  I don't intend to pursue unregulated cobra testing any further at this time.  It was more of a curiosity than anything else....

[mann]

Understood. It's crazy how much of an effect it has on the poppet . I guess I think of it as a air spring with more of an effect at higher pressure

[oldpro]

Understood. It's crazy how much of an effect it has on the poppet . I guess I think of it as a air spring with more of an effect at higher pressure

It works evenly across the board down to very low pressures I actually tried to get mine to burp and blow the valve open but it never did all the way down to 200 psi.

[Motorhead]

Scott predicted the Cobra chamber would result in greater ES than non-cobra and he was correct.  Sometimes I have to see things with my own eyes, this was one of those times.....

Whats that TAG line .... Experience is 

[oldpro]

Scott predicted the Cobra chamber would result in greater ES than non-cobra and he was correct.  Sometimes I have to see things with my own eyes, this was one of those times.....

Whats that TAG line .... Experience is 

Thats only because the strings are twice as long LOL

[triggertreat]

That's a good point Travis.

[mackeral5]

Now that i've seen Cobra effect on a few different applications I have a couple of questions around volume of the Cobra chamber itself.  Travis' thread on his latest project, the Python valve, discusses this topic a bit. 

for 2 Cobra chambers using the same jet, a .056" for example... One just large enough to allow room for the light valve spring and enough travel to not bottom out during valve lift.  The second would be say, 3x the volume.  If I am interpreting things correctly, the smaller in volume the Cobra chamber, the harder the valve will be to open.  The larger volume Cobra chamber will be easier to open due to more room to compress the charge in the Cobra chamber? 

In closing the valve with Cobra affect-----is the Cobra effect greater with a larger volume Cobra Chamber as there is more air to expand???

Thanks in advance.

[oldpro]

 Yes the smaller the cobra chamber the shorter the dwell so getting the power back to previous setting requires more hammer strike so the same goes with larger chamber= less hammer strike but less effect on dwell. Dwell is the time it takes to fully open and close the valve from start to finish and this can be divided into smaller sections. Start/peak/fall/finish.

[Motorhead]

Yes the smaller the cobra chamber the shorter the dwell so getting the power back to previous setting requires more hammer strike so the same goes with larger chamber= less hammer strike but less effect on dwell. Dwell is the time it takes to fully open and close the valve from start to finish and this can be divided into smaller sections. Start/peak/fall/finish.

Been a LONG time sense offering up info on this subject .... reading the last post travis had made WOKE ME UP !
That said is INCORRECT .... and here the why for behind that statement.

Bigger the chambers volume, flowing threw a fixed hole size during the shot cycle ... LESS WILL BE the pressure drop within the chamber than a smaller chamber will see.
Smaller the chambers volume, FASTER the pressure differential will collapse on the same jetting size.
There is TUNING is how quickly or slowly the chamber is allowed to equalize / collapse during the shot cycle.

In the near 15 months sense the post above personally have made many more versions, gotten distracted with the balanced valves and finding myself revisiting "Cobra" tech in lower to mid power applications.
in the past 3-4 months have eclipsed the best of my best in efficiency having had 2 tunes go beyond 2.0 fpe/ci
The most recent and in need of some more validation is this tune in a Highly Modified JSAR Raptor mini ....  https://www.gatewaytoairguns.org/GTA/index.php?topic=171248.msg155960614#msg155960614


Scott S