GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: antithesis on June 16, 2021, 11:57:08 PM
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Ok I need some possible solutions to a problem some designs present.
Some airguns, by design have a ridiculous long path between valve port and barrel port. Is there any way to reduce the disadvantages this presents? I was thinking about seeing if I could have a gradual reduction in port area would cause the flow to pick up speed and not create unnecessary dead volume, meaning slightly larger at the valve and a slow taper to a desired barrel port size?
I am reaching here but have no idea if there is anything to be done to improve flow in a long air path from valve to pellet. Hence I'm fishing for suggestions from the enlightened ones here.
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really pending on guns caliber, power wanted and what size passage is currently.
Fill in those Q's & we can discuss it further
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really pending on guns caliber, power wanted and what size passage is currently.
Fill in those Q's & we can discuss it further
Kral puncher breaker, .22, 30 to 35 ftlbs, and I dont know maybe 1.5 inches to barrel from valve exhaust. Whatever the stock length is
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really pending on guns caliber, power wanted and what size passage is currently.
Fill in those Q's & we can discuss it further
Kral puncher breaker, .22, 30 to 35 ftlbs, and I dont know maybe 1.5 inches to barrel from valve exhaust. Whatever the stock length is
And fwiw I plan on running a huma reg and would like to keep pressure low as necessary. I ordered the 25 style for extra plenum volume
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My nemesis was pushing 18gn JSB over 1000fps with some sort of aftermarket hammer spring.
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My nemesis was pushing 18gn JSB over 1000fps with some sort of aftermarket hammer spring.
I have a interesting situation where I have a maybe 12mm of spring that doesn't ride the rear guide rod, was planning on making a tss for it because with a front guide it's just begging for it
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My nemesis was pushing 18gn JSB over 1000fps with some sort of aftermarket hammer spring.
I have a interesting situation where I have a maybe 12mm of spring that doesn't ride the rear guide rod, was planning on making a tss for it because with a front guide it's just begging for it
That aside, making a long transfer port operate as well as I can is my primary focus atm... I'll let you know when I start working on the TSS system
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I bought my nemy used and dont know much of its history other than it was tuned to be HOT. I think the only major difference is I have a drop block for a bottle, from what I understand is that the rest of the action is the same. Is your goal up to 35FPE because I think a spring like I have would be the easiest way to hit that goal. Outside of that I cannot provide a better answer to get to a FPE value or efficiency by adjusting the transfer port size.
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I bought my nemy used and dont know much of its history other than it was tuned to be HOT. I think the only major difference is I have a drop block for a bottle, from what I understand is that the rest of the action is the same. Is your goal up to 35FPE because I think a spring like I have would be the easiest way to hit that goal. Outside of that I cannot provide a better answer to get to a FPE value or efficiency by adjusting the transfer port size.
I am sure I can get my numbers and get her shooting beautiful if it's the last thing I do. O just know that long air passage isnt optimal and if anyone regardless of the platform has found a way to make the most of it and how they would do it, and maybe the principles behind what they did
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Compensate for the long passage, and the potential pressure drop that creates, by a small increase in pressure.... Flow velocity is important only towards the end of the shot cycle, when the pellet is reaching maximum speed.... Initially, just after the valve cracks, you are dealing only with the effects of pressure.... Port size, port restrictions, and port length have little to do with what happens in the first inch or two of pellet travel, when the acceleration is the highest....
Bob
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Compensate for the long passage, and the potential pressure drop that creates, by a small increase in pressure.... Flow velocity is important only towards the end of the shot cycle, when the pellet is reaching maximum speed.... Initially, just after the valve cracks, you are dealing only with the effects of pressure.... Port size, port restrictions, and port length have little to do with what happens in the first inch or two of pellet travel, when the acceleration is the highest....
Bob
That's a start. I know there isnt any magic number to play with, so I won't ask...it does beg for an experiment though to see what effect the length of passage per inch would have if all other factors were the same.
I suppose I got spoiled by the crosman prod/mrod and even qb platforms that usually have super short air transfer......well there's always those multi shot conversions. Maybe that difference has already been documented on someone's build progress post with those conversions maybe I'll look one day to check it out for my own curiosity
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https://www.gatewaytoairguns.org/GTA/index.php?topic=120119.msg1179362#msg1179362 (https://www.gatewaytoairguns.org/GTA/index.php?topic=120119.msg1179362#msg1179362)
Read reply 25
Some more here https://www.gatewaytoairguns.org/GTA/index.php?topic=153468.msg155688769#msg155688769 (https://www.gatewaytoairguns.org/GTA/index.php?topic=153468.msg155688769#msg155688769)
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If you calculate the volume of the transfer port (from valve seat to pellet base), you add that to the volume of the plenum (or reservoir if unregulated) to get the increased volume before the pellet moves.... That expansion drops the pressure by P1 x V1 = P2 x V2.... which rearranged is P2 = P1 x V1 / V2....
For example, if you start with 2000 psi in the plenum (P1), and have a plenum of 50 cc (V1) and a transfer port volume of 1 cc (expanded volume V2 = 50 + 1 = 51 cc), the pressure available at the start of the shot is 2000 x (50 / 51) = 1961 psi.... If the transfer port volume is 2 cc, same pressure and plenum, you end up with 2000 x (50 / 52) = 1923 psi.... That would require increasing the pressure in the plenum by 38 psi to compensate for the larger transfer port volume....
If the transfer port is significantly smaller than the caliber, then in addition you MAY get a loss in flow because of the additional restriction because of the added length, but that will very much depend on the velocity.... Any such loss would require an additional pressure increase to compensate....
Bob
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If you calculate the volume of the transfer port (from valve seat to pellet base), you add that to the volume of the plenum (or reservoir if unregulated) to get the increased volume before the pellet moves.... That expansion drops the pressure by P1 x V1 = P2 x V2.... which rearranged is P2 = P1 x V1 / V2....
For example, if you start with 2000 psi in the plenum (P1), and have a plenum of 50 cc (V1) and a transfer port volume of 1 cc (expanded volume V2 = 50 + 1 = 51 cc), the pressure available at the start of the shot is 2000 x (50 / 51) = 1961 psi.... If the transfer port volume is 2 cc, same pressure and plenum, you end up with 2000 x (50 / 52) = 1923 psi.... That would require increasing the pressure in the plenum by 38 psi to compensate for the larger transfer port volume....
If the transfer port is significantly smaller than the caliber, then in addition you MAY get a loss in flow because of the additional restriction because of the added length, but that will very much depend on the velocity.... Any such loss would require an additional pressure increase to compensate....
Bob
Wow bob you just pulled that math right up.....you never disappoint.
Scott, thanks for the links I'll have a gander
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https://www.gatewaytoairguns.org/GTA/index.php?topic=120119.msg1179362#msg1179362 (https://www.gatewaytoairguns.org/GTA/index.php?topic=120119.msg1179362#msg1179362)
Read reply 25
Some more here https://www.gatewaytoairguns.org/GTA/index.php?topic=153468.msg155688769#msg155688769 (https://www.gatewaytoairguns.org/GTA/index.php?topic=153468.msg155688769#msg155688769)
Scott,
On the first one was that a reference to the poorly thought out air path inherent to this type of design, or to bring attention to the inherent problems in this type of air choke as a means of velocity control?
And for the second one, I assume is to point out the misalignment frequently seen in these rifles? (Believe me I've noticed and already done SOME work on the issue, and if need be I will be eliminating the chokes ability to turn and run a straight tube through the whole flow path if I can make reliable sealing.
If I misread the point you were trying to show me correct me at your convenience
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yes ... that inconsistencies in path size hurt more than too small or too large.
The rotary ball valve controlling velocity is a major stumbling path in that design.
Valves transfer path exiting throat all the way to and including barrel really optimize in these @ sizes for more powerful field duty type tunes.
.177 cal @ .140"
.22 cal @ .165"
.25 cal @ .180"
GETTING said sizes not so easy on some PCP's
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yes ... that inconsistencies in path size hurt more than too small or too large.
The rotary ball valve controlling velocity is a major stumbling path in that design.
Valves transfer path exiting throat all the way to and including barrel really optimize in these @ sizes for more powerful field duty type tunes.
.177 cal @ .140"
.22 cal @ .165"
.25 cal @ .180"
GETTING said sizes not so easy on some PCP's
That confirms my thoughts about drilling through a straight path big enough to fit about .145 to .155 ID brass or stainless tube through the action for a direct path. I really need to figure out how to secure a reasonable seal on both ends.. that'll be the challenging part but I think itll pay dividends in this case
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Good information. Ive always wondered about this effect. Good to have the math! Thanks.
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Good information. Ive always wondered about this effect. Good to have the math! Thanks.
And that's why I come to "the workshop" for this sort of thing.....I just don't know how he just pulls it out his keister in 2 minutes and gives me the whole synopsis lol....the man is good I'll say that much
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yes ... that inconsistencies in path size hurt more than too small or too large.
The rotary ball valve controlling velocity is a major stumbling path in that design.
Valves transfer path exiting throat all the way to and including barrel really optimize in these @ sizes for more powerful field duty type tunes.
.177 cal @ .140"
.22 cal @ .165"
.25 cal @ .180"
GETTING said sizes not so easy on some PCP's
If I might ask-what you would consider a more powerful field tune in .22?
Jesse
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yes ... that inconsistencies in path size hurt more than too small or too large.
The rotary ball valve controlling velocity is a major stumbling path in that design.
Valves transfer path exiting throat all the way to and including barrel really optimize in these @ sizes for more powerful field duty type tunes.
.177 cal @ .140"
.22 cal @ .165"
.25 cal @ .180"
GETTING said sizes not so easy on some PCP's
If I might ask-what you would consider a more powerful field tune in .22?
Jesse
30 fpe and above
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Thanks Scott,
Jesse
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yes ... that inconsistencies in path size hurt more than too small or too large.
The rotary ball valve controlling velocity is a major stumbling path in that design.
Valves transfer path exiting throat all the way to and including barrel really optimize in these @ sizes for more powerful field duty type tunes.
.177 cal @ .140"
.22 cal @ .165"
.25 cal @ .180"
GETTING said sizes not so easy on some PCP's
If I might ask-what you would consider a more powerful field tune in .22?
Jesse
30 fpe and above
Even in .177?
Well with the slugs that are available now I suppose it's more realistic and practical than it used to be. ....a .177 at 30 ftlbs is going to be tough. And impractical but alot of people insist so......can lead a horse to water but cant make him use a .22😆
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The 30 FPE was the answer to the question of what was a "more powerful filed tune in .22".... In similar guns (barrel length, pressure, etc.) that would be ~20 FPE in .22 cal and ~40 FPE in .25 cal.... Personally, for field tunes for pellets, I would use slightly larger ports in .25 cal (0.188").... For slugs, and with the intent of more power, I would be using as close to bore-area porting as possible in all calibers.... but only if the probe is also retractable.... otherwise I would just match the chamber area (bore area minus probe area) with all porting.... and about 10% larger than that for the valve throat....
Bob
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The 30 FPE was the answer to the question of what was a "more powerful filed tune in .22".... In similar guns (barrel length, pressure, etc.) that would be ~20 FPE in .22 cal and ~40 FPE in .25 cal.... Personally, for field tunes for pellets, I would use slightly larger ports in .25 cal (0.188").... For slugs, and with the intent of more power, I would be using as close to bore-area porting as possible in all calibers.... but only if the probe is also retractable.... otherwise I would just match the chamber area (bore area minus probe area) with all porting.... and about 10% larger than that for the valve throat....
Bob
Oh. He DID say in .22. Ok I'll shut up.
I am settling on 4mm or very close porting and upping the reg a tiny bit if necessary.
I was kicking ideas around with TH and he seems to be sure I'll be better off unregulated.
Who knows maybe I'll be selling an unused huma keep your eyes peeled.