JSAR SS Valve is better than ever!

[nervoustrigger]

Okay thanks, I was just thinking it could be a combination of stiction and regulator creep.

[wimpanzee]

Starting to wonder if this is going on with mine, too. I have a huma regulated jsar valve at 1750psi. I only shot a few shots to tune it to jsb 15.89@890fps, and didn't do a full shot string.

Shooting it though, I'll get flyers and then groups tighten up as I shoot more. I'll have to get the chrony and do some periodic testing as well, and report back.

[triggertreat]

Okay thanks, I was just thinking it could be a combination of stiction and regulator creep.

I can say, at the moment, my Huma is rock solid and without creep.  I did fight with creep until I rebuilt it months back.  Now it's the last thing I'm concerned with as it's the same every time I check it.

[AlanMcD]

Mine is a Huma regged .25, and I did not have much luck with stability until I got close to around 2000 psi.  It is currently set at ~2100 psi for a fairly high power tune (about 52 FPE with JSB 34 grain pellets), and have had it this way for over 6 months, and I checked the velocity a few weeks back and it was stable on the first shot.  It probably has about 600-700 shots through it at this set up, so the o-rings are well set, and it holds air with no leaks over weeks.

This is my second Huma regulator - the other is in a .22 Marauder.  That one was rock solid for about 5 years then I had to rebuild it as it started to creep - and it is back to rock solid again.  I will take that maintenance schedule.

[skorec]

i haven’t followed all the details leading up to this point so this may be a dumb question but is this stiction symptom present with unregulated setups?

I am running it  not regulated for now and first shot handicap  is a little bit les by using it around  3000 PSI. I reduce/adjust the power rader via choking air transfer way at my Puncher mega  .177
Also when I clean and lube entrance of SS valve with  Teflon spray  first shot handicap is a little bit less. Approximately after one month first shot  velocity handicap return back . 

[mann]

Why the orings could not a person get enough of a seal to leave them out to get rid of sticktion problems . Or does it have to be sealed up on that end to make it work . Otherwise you could adjust the jet size to help with some leak by . What am I missing

[Motorhead]

Must be sealed up x2 ...
The cobra tube requires a seal so the captive pressure minus what bleeds off via the jet actually forces the poppet to close. If this o-ring leaks or is absent it allows air into the balance chamber.
The balance chamber is connected to the throat via a drilled passage threw the poppet stem and if this o-ring leaks the containment pressure within valve takes that path exiting out barrel.
The balance chamber uses the Cobra tube o-ring at one end & has the primary poppet o-ring at the other end.

BOTH must be in place and offer 100% seal integrity for the system to work.

[mann]

Thanks for explaining helps me understand the valve better

[skorec]

I have mentioned here already the idea  to recompense  front jet chamber by some  spring  but it is probably stupid idea because no one react on it .
If I understand front jet  chamber right it acts  as high air pressure flexible bumper at open phase and  then as blank holder of poppet to  stay closed enough.
Am I wrong ?

[Motorhead]

I have mentioned here already the idea  to recompense  front jet chamber by some  spring  but it is probably stupid idea because no one react on it .
If I understand front jet  chamber right it acts  as high air pressure flexible bumper at open phase and  then as blank holder of poppet to  stay closed enough.
Am I wrong ?

The Cobra chamber as you state ALREADY CONTAINS A SPRING ... that is in place so an empty gun can be filled, it overcomes the static sticktion of the o-rings pushing poppet against the seat.
Compared to the closing force of the captive high pressure air within the tube, the springs actual contribution is very very small.

[skorec]

I have mentioned here already the idea  to recompense  front jet chamber by some  spring  but it is probably stupid idea because no one react on it .
If I understand front jet  chamber right it acts  as high air pressure flexible bumper at open phase and  then as blank holder of poppet to  stay closed enough.
Am I wrong ?

The Cobra chamber as you state ALREADY CONTAINS A SPRING ... that is in place so an empty gun can be filled, it overcomes the static sticktion of the o-rings pushing poppet against the seat.
Compared to the closing force of the captive high pressure air within the tube, the springs actual contribution is very very small.

.[/color]

YES I know.

You are meaning probably front chamber with jet if you have written  cobra chamber.

I am thinking that :
1.   Cracking/opening  force is proportional to calibre  of front chamber and air tube pressure  plus inside spring force.
2.   Start closing force is proportional to calibre  of front chamber and higher air pressure plus higher spring force + poppet calibre and  air tube pressure.
3.   End closing force is proportional to calibre  of front chamber and air tube pressure  plus inside spring force + poppet calibre and  air tube pressure.

If the  jet of front/cobra  chamber will be  much larger we lose only :
a, flexible bumping effect
b, higher start closing force

Am I wrong ?

[triggertreat]

I have been checking for stiction in my new SS valve and it doesn't look like it's going away anytime soon with my current hammer and spring setup.  It's not real bad, but my .25 is a hunter and I can't have any stiction issues.  I do believe I can fix the issue and will be playing around with different spring setups and maybe a different hammer as I have others to play around with.  I really don't blame the valve, but blame myself for how I have it setup knowing how the valve is designed.  I keep setting it up like a traditional valve and not a state of the art balanced valve.  I love this valve and I don't whine or give up so easily.

[skorec]

  I love this valve and I don't whine or give up so easily.

I too.
 
Yesterday I have polished/lapped bough chambers with rottenstone , change O-rings and lubed with teflon spray .  The first shot velocity handicap decrease a little bit again.

I am thinking that use lube which is stable ( some non drying oil  especially at HPA area ) is most important.
I am not sure at all if the Teflon lube is the best !!!

[nervoustrigger]

If reducing O-ring stiction is the goal, it looks like FEP is the material of choice:
https://web.wpi.edu/Pubs/E-project/Available/E-project-102112-214155/unrestricted/NAG1202-Investigation_of_O-ring_Adhesion_in_Space_Mechanisms.pdf  (refer to page 37)
https://en.wikipedia.org/wiki/Fluorinated_ethylene_propylene

If that's too hard to find, this article claims Viton (FKM) to have low breakout friction:
http://www.o-rings.com/would-slippery-o-rings-or-seals-improve-your-product-performance/

[skorec]

Thanks,

I have read that Viton  swell by air pressure.    

[mann]

That maybe the fix we need ptfe encapsulated or fep encapsulated o-rings  I searched them and there are a few companies that offer them just no pricing

[triggertreat]

I truly hope we can ban together and resolve this issue.  I don't know the sizes of the O-rings.  Lubes I assume will deteriorate eventually.  I'm going to dabble with an oil lube along with some preload.  I know the valve can handle some preload without efficiency loss.  I'm also going to try a much heavier hammer.  None of this may work, but the stiction is not real severe in mine.  It's just enough to disappoint, but not enough to throw it in the dirt.

[mann]

No I agree there has to be something that can fix it other than that one shot it's great I'm going to stay running it I might try to find some viton orings and give that a go I don't know the oring sizes either but that would help

[mann]

Does anyone know oring sizes in the ss valve would like to try a couple different types but need the sizes

[nervoustrigger]

Yeah I hope you guys can get it sorted out.  I sympathize with the importance of first-shot reliability in hunting situations.

Since Viton is easy to obtain, I would be tempted to try it and run a before and after trial to see if it shows some improvement...and if so, then work on sourcing the FEP.  Perhaps burnish a dry lube onto the O-ring and its mating surface.  I imagine PTFE would be one of the best for this purpose but I wouldn’t hesitate to try graphite.  For example, I know if you smear graphite onto a piece of rubber, it loses its grip against a smooth surface.  Like you said, I’m not sure how long it will last but surely long enough for a test over a few days’ time.

Regarding Viton swelling, yes that’s what I’ve observed but compared to the pressure forcing it against its mating surface, the added friction component would be academic I think.