JSAR SS Valve is better than ever!

[KnifeMaker]

IN noticing several mentions of Graphite, remember, it is corrosive to bare aluminum.


Knife

[Hobbyman2007]

https://www.theoringstore.com/index.php?main_page=index&cPath=14

here is a thought from my monkey brain..a backup ring on one side of the o-ring

I’ve always wondered why no one used backup rings . Works wonders with proportional hydraulic systems . I have a good assortment and will do some testing on my cobra setup once I get a chance.

[Wayne52]

I kick myself in the butt for not sending mine in yet, I was going to do it at least a week ago but I've just got so many irons in the fire so to speak right now.  Seems like I'm always testing pellets, working on other guns and the list goes on.  But still at the top of the list is getting out hunting with them.  I'll be out shooting my DAR25 later this morning, the thing is just shooting the 26 grainers so nice I can't stop.

[nervoustrigger]

Knife, isn’t that a galvanic corrosion between dissimilar metals?  Like where aluminum is against steel?  It would not apply to an O-ring on aluminum.

[PCPhack]

I believe that FEP orings, square orings, higher durometer orings, and backer orings are 4 possibilities that warrant testing.

[triggertreat]

IN noticing several mentions of Graphite, remember, it is corrosive to bare aluminum.


Knife

My thimble is brass.

[SilentMatt]

We've tried to source coated O-rings with no luck so far and many companies have stated that the coating wouldn't last long anyway.

Brake caliper pistons use a square cut o-ring to pull the piston back into the bore, don't think that'll help here.

And yes, all the thimbles are brass.

[Motorhead]

What is a "Sticking Point" ... yes pun intended.
Is that a conventional poppet valve is a passive devise where as the seal containing the high pressure is that of a simple cork over hole design.  There is no o-rings within the valve that controls or seals exit & flow of HPA to the pellet other that the transfer path.

So now we enter the realm of a valve where the design has not just 1 but 2 o-rings that keep the poppet from leaking HPA having nothing to do with the seat seal that ultimately controls HPA flow to the pellet 
These o-rings just sit there in a STATIC position and bear the load upwards of 3000 psi.  They will deform wanting to be smashed against the groove / gland just like every other o-ring that seals the HPA containment !
When the gun is fired these 2 STATIC o-rings are required to do a DYNAMIC sealing function too and really feel this is where the design problem runs into a compromised situation 
An o-ring that is no longer semi round bearing a pressure load simply can't act the same as the same o-ring in a static load with no pressure bearing against it.

I'm really not sure if there is a work around to the issue of initial sticktion
Certainly o-ring material type come into play, but with such SMALL 1mm cross section o-rings this is a very tall order indeed !

Just thinking and sharing thoughts on whats going on.

Scott

[PCPhack]

In the case of my Bulldog, I tuned around it. The loss of first shot FPS is very repeatable, and shows up after the rifle sits for just a short time. The FPS loss doesn't appear to increase very much after that. So I increased my spring load a bit and found a place where my first shot, and then even a follow up shot are within 10 fps of each other. This is my hunting tune. If I am target shooting, I just tether at the pressure equal to that second shot, a few hundred psi less in the case of my Bulldog. Since I will always have a delay between making the rifle ready, and arriving at a hunting spot, this works well for me so far. This is how I deal with it now, but it will be nice if we find a way to improve the design.

[nervoustrigger]

What about adding PTFE to the list of things to try?
 
Industry figures say you don’t want to stretch it more than 5% - 10% so the thimble would need to be a 2-piece construction.  That makes it more expensive to manufacture but if the properties of PTFE solve the issue, it would be worth it.   FWIW, the final stage of a Chinese high pressure pump I worked on has a brass “hat” that unthreads from the end of the shaft.  This feature wasn’t necessary to replace the O-ring but it gave access to replace the rigid backer ring that accompanied it.  Same idea.
 
Regarding the question of whether PTFE’s properties are good for this role, frankly I don’t know but it just might.  It’s slick as snot so it has that going for it.  And it’s a plastic, not rubber (elastomer).  It cold flows to match the shape of the parts.  So if we think about what is happening whenever the thimble is being knocked free, a traditional O-ring wants to stick because it is soft and compliant.  Contrast that with a relatively hard, dense PTFE.  It doesn’t change shape instantaneously the way an elastomer does so I’m thinking it would break free more consistently.
 
If that alone does not sufficiently reduce/stabilize the stiction, perhaps the wall could be given a slight taper.  That way the instant the thimble breaks free, the PTFE loses contact with the walls so there’s no drag.  Seems like that would further improve consistency.
 
I haven’t investigated what the geometry would need to be to ensure normal operation pressures don’t cause the material to extrude to the point of failure so that might be the challenge.  A backer ring is one possible answer but apparently there are also filler options like bronze that reduce cold flow.
https://www.alliedmetrics.com/seals/o-rings/ptfe-o-rings.php
Notice also molybdenum disulfide for better sliding properties.

[oldpro]

What about adding PTFE to the list of things to try?
 
Industry figures say you don’t want to stretch it more than 5% - 10% so the thimble would need to be a 2-piece construction.  That makes it more expensive to manufacture but if the properties of PTFE solve the issue, it would be worth it.   FWIW, the final stage of a Chinese high pressure pump I worked on has a brass “hat” that unthreads from the end of the shaft.  This feature wasn’t necessary to replace the O-ring but it gave access to replace the rigid backer ring that accompanied it.  Same idea.
 
Regarding the question of whether PTFE’s properties are good for this role, frankly I don’t know but it just might.  It’s slick as snot so it has that going for it.  And it’s a plastic, not rubber (elastomer).  It cold flows to match the shape of the parts.  So if we think about what is happening whenever the thimble is being knocked free, a traditional O-ring wants to stick because it is soft and compliant.  Contrast that with a relatively hard, dense PTFE.  It doesn’t change shape instantaneously the way an elastomer does so I’m thinking it would break free more consistently.
 
If that alone does not sufficiently reduce/stabilize the stiction, perhaps the wall could be given a slight taper.  That way the instant the thimble breaks free, the PTFE loses contact with the walls so there’s no drag.  Seems like that would further improve consistency.
 
I haven’t investigated what the geometry would need to be to ensure normal operation pressures don’t cause the material to extrude to the point of failure so that might be the challenge.  A backer ring is one possible answer but apparently there are also filler options like bronze that reduce cold flow.
https://www.alliedmetrics.com/seals/o-rings/ptfe-o-rings.php
Notice also molybdenum disulfide for better sliding properties.

Because PTFE is such a dense material, it cannot be “melt-processed”.  It must be compressed and sintered to form useful shapes (like o-rings).
 

[nervoustrigger]

Travis, are you saying that statement precludes it from being used in this application?  I took that statement as dealing with how PTFE seals are made rather than how they are used.

[mobilehomer]

Travis, I have been pondering this stiction situation since it was mentioned in this thread. An observation, since the o-rings really don't seal the hpa, (after all, after just a few seconds, the pressure equalizes on both sides of the orifice) it acts more like the piston in a springer pushing air through the orifice to control the speed of the poppet, does the o-ring need as much squish as a true sealing o-ring? Instead of a .010" squish, would a .005" work just as well with less stiction? Just a suggestion.

[Jacob_M]

I've been shooting with the SS valve for about a month now. No matter which way I try it, it likes to be hit hard. Today I shot a  51 Shot string. Regulator set to 2000psi. First shot 831 and last shot 830.ES was 16 and SD was 3. Maybe I could have extended it more, but I ran out of the 34 gr. jsbs.

Before shooting the gun it sat all day in a cold house since I forgot to turn on the heater. I have a TSS installed with the springs it came with and the MDS super hammer. The striker has been cut and screwed flush with the hammer face. There is nearly no gap between the hammer face and valve pin. So I feel like it is hitting the valve pretty hard and I'm getting good consistency from the beginning till the end of the shot string. Whenever I gave it more gap(less fps in attempt to get more shots) my ES went to 30+. This is just my experience with the SS valve. Its max power for the given regulated pressure or you get less consistent strings. Maybe my less consistent strings had something to do with stiction, I'm ok with running highest power only since I'm getting 50+ shots per fill.



 

[mann]

I picked up a viton oring kit might be able to use a couple out of the kit and try it if some fit

[triggertreat]

I've been shooting with the SS valve for about a month now. No matter which way I try it, it likes to be hit hard. Today I shot a  51 Shot string. Regulator set to 2000psi. First shot 831 and last shot 830.ES was 16 and SD was 3. Maybe I could have extended it more, but I ran out of the 34 gr. jsbs.

Before shooting the gun it sat all day in a cold house since I forgot to turn on the heater. I have a TSS installed with the springs it came with and the MDS super hammer. The striker has been cut and screwed flush with the hammer face. There is nearly no gap between the hammer face and valve pin. So I feel like it is hitting the valve pretty hard and I'm getting good consistency from the beginning till the end of the shot string. Whenever I gave it more gap(less fps in attempt to get more shots) my ES went to 30+. This is just my experience with the SS valve. Its max power for the given regulated pressure or you get less consistent strings. Maybe my less consistent strings had something to do with stiction, I'm ok with running highest power only since I'm getting 50+ shots per fill.

I'm surprised you only got 51 shots with that Brod you got with a 350cc tank filled to 4400-4500psi.

[Jacob_M]

I could have kept going but I ran out of pellets. I currently have 2500psi of air left. I’m pretty confident I can get 2 more mags out of it before coming off the regulator. I will finish up the shot string tomorrow.

[oldpro]

I picked up a viton oring kit might be able to use a couple out of the kit and try it if some fit

Viton swells under pressure it will make stiction way worse.

[SilentMatt]

What about adding PTFE to the list of things to try?
 
Industry figures say you don’t want to stretch it more than 5% - 10% so the thimble would need to be a 2-piece construction.  That makes it more expensive to manufacture but if the properties of PTFE solve the issue, it would be worth it.   FWIW, the final stage of a Chinese high pressure pump I worked on has a brass “hat” that unthreads from the end of the shaft.  This feature wasn’t necessary to replace the O-ring but it gave access to replace the rigid backer ring that accompanied it.  Same idea.
 
Regarding the question of whether PTFE’s properties are good for this role, frankly I don’t know but it just might.  It’s slick as snot so it has that going for it.  And it’s a plastic, not rubber (elastomer).  It cold flows to match the shape of the parts.  So if we think about what is happening whenever the thimble is being knocked free, a traditional O-ring wants to stick because it is soft and compliant.  Contrast that with a relatively hard, dense PTFE.  It doesn’t change shape instantaneously the way an elastomer does so I’m thinking it would break free more consistently.
 
If that alone does not sufficiently reduce/stabilize the stiction, perhaps the wall could be given a slight taper.  That way the instant the thimble breaks free, the PTFE loses contact with the walls so there’s no drag.  Seems like that would further improve consistency.
 
I haven’t investigated what the geometry would need to be to ensure normal operation pressures don’t cause the material to extrude to the point of failure so that might be the challenge.  A backer ring is one possible answer but apparently there are also filler options like bronze that reduce cold flow.
https://www.alliedmetrics.com/seals/o-rings/ptfe-o-rings.php
Notice also molybdenum disulfide for better sliding properties.

 The poppet would actually need to be 3 pieces as it has two O-rings, and with how small it is that isn't going to happen. I think we'd also run into sealing issues.

Travis, I have been pondering this stiction situation since it was mentioned in this thread. An observation, since the o-rings really don't seal the hpa, (after all, after just a few seconds, the pressure equalizes on both sides of the orifice) it acts more like the piston in a springer pushing air through the orifice to control the speed of the poppet, does the o-ring need as much squish as a true sealing o-ring? Instead of a .010" squish, would a .005" work just as well with less stiction? Just a suggestion.

 The O-rings keep HPA from leaking into the vent in the stem.

[nervoustrigger]

Hi Matt, okay thanks for commenting on the difficulties of making the part accommodate a semi-rigid seal.
 
I have a question that relates to Mobilehomer’s comment and your answer.  If I’m understanding you correctly, there is indeed a differential pressure across the O-rings when the poppet is at rest.  Is that right?  That makes more sense to me because otherwise there would be no pressure squeezing the O-ring against the wall to make it want to stick…none other than that which is dictated by how tightly the parts are fitted in which case it would be as he said, something you could address by simply modifying the part dimensions.
 
That also suggest a Viton O-ring’s tendency to swell won’t necessarily cause it to exert a substantially higher force on the surrounding wall because it represents a tiny fraction compared to the high pressure air that is squeezing it, pressing it against the wall.  That’s not to say I’m asserting some confidence Viton’s lubricity will substantially improve things compared to, say, Buna-N but I’m a bit skeptical that it’s likely to make things substantially worse.