Quote from: PikeP on December 28, 2021, 11:37:27 AMFully balance the valve, use minimum spring rating with a softer material to achieve your seal (this would take trial and error as it depends on material used, sealing surface diameter, and spring used)Then play with larger valve stem sizes, since that is, as you put, primary closing force (which it is in smaller calibers that move little air). If you're talking about a 10-30 fpe rifle with a balance valve, opposed to where they're really needed (150+ fpe rifles), the air movement through the valve is far less, and not as concerning.Essentially, no one has the answer except trial and error. If you have 120 lbs holding a poppet shut right now, and 25 lbs of closing force, your hammer strike is absorbed by both, but no one has a true answer as to what % of that strike is left fighting the 25 lbs of closing force in a very small caliber, probably marginal when compared to the 120 initial #'s holding the valve shut...introducing a larger valve stem diameter thru the valve body would re-introduce hammer strike sensitivity.Is it possible? Sure. Is it practical? Maybe? Does anyone currently have all the answers? No.My 100# recommendation at pressure holding a valve shut is mostly for practical purposes and safety precautions.You also have to consider, if you make a valve open too easily, the hammer strike needed to open it becomes, slow, lazy, weak, and with that more sensitive itself to variation, this is where you find yourself only lightening the hammer itself while keeping the same spring rating, and the end result? A ms or two shaved off hammer lock time which is already in the sub 10 msec range....Also consider, what is the lightest hammer + spring you would want in your rifle. IMO its vital to find the ideal combo here, where the hammer is not too light, nor heavy, and the spring not too stiff, nor too light... I have all the formulas to approximate that personally, which makes it easier to have my perspective. If one wanted to do a lot of work for near nothing, I suppose they could run a short throw, stiffly sprung, light to medium weight hammer to achieve an incredibly low lock time with a near fully balanced valve, seems like a lot of work to me to cut off a few MS of hammer lock time though...so, to me, that is about the only reason to go this route...A light hammer spring would be good for my build, I was thinking of converting one of my BSAs to a balanced valve and to use this "Caselman" principle for cycling: https://www.gatewaytoairguns.org/GTA/index.php?topic=155499.0
Fully balance the valve, use minimum spring rating with a softer material to achieve your seal (this would take trial and error as it depends on material used, sealing surface diameter, and spring used)Then play with larger valve stem sizes, since that is, as you put, primary closing force (which it is in smaller calibers that move little air). If you're talking about a 10-30 fpe rifle with a balance valve, opposed to where they're really needed (150+ fpe rifles), the air movement through the valve is far less, and not as concerning.Essentially, no one has the answer except trial and error. If you have 120 lbs holding a poppet shut right now, and 25 lbs of closing force, your hammer strike is absorbed by both, but no one has a true answer as to what % of that strike is left fighting the 25 lbs of closing force in a very small caliber, probably marginal when compared to the 120 initial #'s holding the valve shut...introducing a larger valve stem diameter thru the valve body would re-introduce hammer strike sensitivity.Is it possible? Sure. Is it practical? Maybe? Does anyone currently have all the answers? No.My 100# recommendation at pressure holding a valve shut is mostly for practical purposes and safety precautions.You also have to consider, if you make a valve open too easily, the hammer strike needed to open it becomes, slow, lazy, weak, and with that more sensitive itself to variation, this is where you find yourself only lightening the hammer itself while keeping the same spring rating, and the end result? A ms or two shaved off hammer lock time which is already in the sub 10 msec range....Also consider, what is the lightest hammer + spring you would want in your rifle. IMO its vital to find the ideal combo here, where the hammer is not too light, nor heavy, and the spring not too stiff, nor too light... I have all the formulas to approximate that personally, which makes it easier to have my perspective. If one wanted to do a lot of work for near nothing, I suppose they could run a short throw, stiffly sprung, light to medium weight hammer to achieve an incredibly low lock time with a near fully balanced valve, seems like a lot of work to me to cut off a few MS of hammer lock time though...so, to me, that is about the only reason to go this route...
Smaller vent to get more dwell, or larger volume in the balancer with same port size. Transfers can be bigger than caliber, no matter what some say about wasted volume.Marko
... My current poppet modifications do not provide enough valve dwell. I can create a very efficient tune, but it is at relatively low energy levels, those that you would expect out of a well tuned short barreled pcp, not taking advantage of the longer barrel.I believe I need to decrease stem vent size and will soon test that. Bob, Scott, others that have real world experience-----anything to add? thanks in advance.
Quote from: mackeral5 on February 08, 2023, 08:34:29 AM... My current poppet modifications do not provide enough valve dwell. I can create a very efficient tune, but it is at relatively low energy levels, those that you would expect out of a well tuned short barreled pcp, not taking advantage of the longer barrel.I believe I need to decrease stem vent size and will soon test that. Bob, Scott, others that have real world experience-----anything to add? thanks in advance.I'm using a Cothran valve in my Armada big bore. Cothran valves like long barrels. I needed more dwell to take advantage of my even longer barrel (48"). I made a thin section washer to space the front grate out 0.030" for some additional balance chamber volume. And then I trimmed the piston head pack 0.030" to gain even morel balance chamber volume. It helped a little.https://www.gatewaytoairguns.org/GTA/index.php?topic=183218.msg156376705#msg156376705
This Scott knows Nothing of Cothrin valves. Tho conversations of cause & effect of altering dwell parallel the JSAR architecture valves.Indeed chamber volume being lower speed up closing, as does larger venting & Visa Versa.* I've NOT read if or not choking the transfer flow speed up a Cothrin in closing w/o adversely cutting back on power much ( Sonic choking )In JSAR types, if running rather small vented and dwell is a tad longer than wanted, simply adding a bit of progessive transfer restriction causes valve to chop dwell in a pretty controlled manor.
… The poppet mods I described make for a much more efficent vslve. Im my conversations with Don over the years he made it very clear that his design intent did not heavily weight efficiency...a powerful first shot, with backup shots at lower, but acceptable velocities accomplished his primary goals. Many of us want to have our cake and eat it too.....
Followup to post 743... I never measured the vent size in the valve mentioned because it worked so well and it was such a frustrating experience getting it to work I was afraid to touch anything. At the time I didn't really grasp what change truly yielded the more favorable results. Today I measured the vent. It was almost .060, which BTW, worked very well in a short barreled .300 ported .357 pellet/light slug shooter. In longer barrels and when attempting to go for higher energy levels I was having to really lean on the HST, excessively preloading the SSG against the valve and things would become very inefficient not to mention hard to cock.I soldered closed the brass plug that I previously plugged the chamber end of the Cothran stem with. Then I decided to start with the smallest bit I felt safe using , which ended up being .025.I had a 18" .25 Green Mountain barrel with the choke removed in the Brod at the time of first testing. I proceeded to do some testing by using just the Brod tube with the Mrod fill adapter screwed in and connected to my regulated tanks. To start I set the SSG at 2 turns of preload against the valve and started testing at 3000psi.At 3kpsi it would push unsized, a bit hard to chamber MP Molds 6.35mm 48gr airgun bullets upwards of 930-940fps. This is the fasted I've ever pushed these out of the relatively short barrel. Down at 2400psi they would do 840-850fps. The smaller vent is indeed helping with dwell. Shot cycle sounded a lot better too, I believe since the hammer was no longer trying to force the valve to dwell longer than it wanted to.I did more testing with the 24" .300 barrel and results were very similar. With the few JSB 44gr I had left I was able to do some lower pressure testing and I found a nice setting of 1700 psi and approximately 900fps. Once my molds arrive I hope to cast up some pellets and see how it will shoot with a similar tune. I appreciate everyone contributing their experiences.
Quote from: mackeral5 on February 12, 2023, 04:25:07 PMFollowup to post 743... I never measured the vent size in the valve mentioned because it worked so well and it was such a frustrating experience getting it to work I was afraid to touch anything. At the time I didn't really grasp what change truly yielded the more favorable results. Today I measured the vent. It was almost .060, which BTW, worked very well in a short barreled .300 ported .357 pellet/light slug shooter. In longer barrels and when attempting to go for higher energy levels I was having to really lean on the HST, excessively preloading the SSG against the valve and things would become very inefficient not to mention hard to cock.I soldered closed the brass plug that I previously plugged the chamber end of the Cothran stem with. Then I decided to start with the smallest bit I felt safe using , which ended up being .025.I had a 18" .25 Green Mountain barrel with the choke removed in the Brod at the time of first testing. I proceeded to do some testing by using just the Brod tube with the Mrod fill adapter screwed in and connected to my regulated tanks. To start I set the SSG at 2 turns of preload against the valve and started testing at 3000psi.At 3kpsi it would push unsized, a bit hard to chamber MP Molds 6.35mm 48gr airgun bullets upwards of 930-940fps. This is the fasted I've ever pushed these out of the relatively short barrel. Down at 2400psi they would do 840-850fps. The smaller vent is indeed helping with dwell. Shot cycle sounded a lot better too, I believe since the hammer was no longer trying to force the valve to dwell longer than it wanted to.I did more testing with the 24" .300 barrel and results were very similar. With the few JSB 44gr I had left I was able to do some lower pressure testing and I found a nice setting of 1700 psi and approximately 900fps. Once my molds arrive I hope to cast up some pellets and see how it will shoot with a similar tune. I appreciate everyone contributing their experiences. More followup.... The smaller vent has significantly reduced the amount of hammer strike required. Had I not been so thick-skulled in this area I could have saved pounds of lead and many cubic feet of nitrogen, lol... I use a flat wire.spring in this gun's SSG. With the previous .060 vent I used 1 and a half 17lb springs.. After reducing the vent to .025 the first few test shots indicated excessive hammer strike. Even with the SSG adjusted to a half inch of hammer gap/free flight, I still could not adjust down off the plateau.Ultimately i removed the half spring and restored adjustability. and now cocking effort is significantly reduced. I currently do not use any sort of hammer buffer/bumper nor any adjustability in the stiker. Stem protrusion is such that the balance chamber/piston cannot bottom out before the hammer contacts the valve body, IIRC, stem protrusion measures in the .190 range. Any benefit to adding adjustability and/or buffering to the hammer system?
Quote from: mackeral5 on February 17, 2023, 07:44:14 AMQuote from: mackeral5 on February 12, 2023, 04:25:07 PMFollowup to post 743... I never measured the vent size in the valve mentioned because it worked so well and it was such a frustrating experience getting it to work I was afraid to touch anything. At the time I didn't really grasp what change truly yielded the more favorable results. Today I measured the vent. It was almost .060, which BTW, worked very well in a short barreled .300 ported .357 pellet/light slug shooter. In longer barrels and when attempting to go for higher energy levels I was having to really lean on the HST, excessively preloading the SSG against the valve and things would become very inefficient not to mention hard to cock.I soldered closed the brass plug that I previously plugged the chamber end of the Cothran stem with. Then I decided to start with the smallest bit I felt safe using , which ended up being .025.I had a 18" .25 Green Mountain barrel with the choke removed in the Brod at the time of first testing. I proceeded to do some testing by using just the Brod tube with the Mrod fill adapter screwed in and connected to my regulated tanks. To start I set the SSG at 2 turns of preload against the valve and started testing at 3000psi.At 3kpsi it would push unsized, a bit hard to chamber MP Molds 6.35mm 48gr airgun bullets upwards of 930-940fps. This is the fasted I've ever pushed these out of the relatively short barrel. Down at 2400psi they would do 840-850fps. The smaller vent is indeed helping with dwell. Shot cycle sounded a lot better too, I believe since the hammer was no longer trying to force the valve to dwell longer than it wanted to.I did more testing with the 24" .300 barrel and results were very similar. With the few JSB 44gr I had left I was able to do some lower pressure testing and I found a nice setting of 1700 psi and approximately 900fps. Once my molds arrive I hope to cast up some pellets and see how it will shoot with a similar tune. I appreciate everyone contributing their experiences. More followup.... The smaller vent has significantly reduced the amount of hammer strike required. Had I not been so thick-skulled in this area I could have saved pounds of lead and many cubic feet of nitrogen, lol... I use a flat wire.spring in this gun's SSG. With the previous .060 vent I used 1 and a half 17lb springs.. After reducing the vent to .025 the first few test shots indicated excessive hammer strike. Even with the SSG adjusted to a half inch of hammer gap/free flight, I still could not adjust down off the plateau.Ultimately i removed the half spring and restored adjustability. and now cocking effort is significantly reduced. I currently do not use any sort of hammer buffer/bumper nor any adjustability in the stiker. Stem protrusion is such that the balance chamber/piston cannot bottom out before the hammer contacts the valve body, IIRC, stem protrusion measures in the .190 range. Any benefit to adding adjustability and/or buffering to the hammer system? I tested with a -118 oring as a buffer. With such a short stem protrusion this did not allow for the valve to fully open. Velocities should have been above 880fps, with the buffer velocities would not exceed 770fps. This particular hammer is not equipped with an adjustable striker, so I could not make any adjustments, perhaps an adjustable striker combined with the oring buffer would yield more desirable results.