valve question
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valve question
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Topic: valve question (Read 641 times))
JPSAXNC
Sharp Shooter
Posts: 508
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Real Name: James
valve question
«
on:
September 08, 2021, 11:01:12 AM »
Does the air force condor have a balanced valve? TIA
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USA, North Carolina, Saxapahaw
Rob M
GTA Senior Contributor
Posts: 6308
Re: valve question
«
Reply #1 on:
September 08, 2021, 12:44:34 PM »
nope.. but its certainly not conventional .. Someone else will have to explain it .
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Louisiana
scion19801
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Real Name: Dan
Re: valve question
«
Reply #2 on:
September 08, 2021, 01:53:11 PM »
its an interesting mix that airforce has for its valve design.
I say its almost like a constant full force/ full pressure now style valve. yet it does have a valve spring like a conventional valve. but there is more magic going on as well. the heavier the projectile, the longer the valve will stay open to deliver the shot. projectile weight can/does contribute to the dwell time of the valve. yet the fill pressure in the bottle itself also has influence on how the valve works.
It is a crazy interesting animal, that once you learn how it works and gain control of it can turn the airforce guns from mild mannered to and absolute beast.
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USA, NY, Ithaca
Umarex Gauntlet .25, Hawke vantage 3-12x44 sf, jsar super tune kit, adjustable flex regulator, .38l bottle, rocker1 LDC
Airforce Condor .25 cal, Custom LDC. .145" tophat, power wheel 10, 24-2500 psi fills. 3d printed bipod adapter. Nikko mountmaster 3-12x50AO
FX Impact MK2 700mm .25 cal, element helix 6-24x50, slug kit, both superior liners, slug A liner, carbon fiber barrel liners. .22 stx original pellet liner and slug A liner in 700 mm. .30 cal superior liner. tuner shroud for 700mm.
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sb327
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Real Name: David
Re: valve question
«
Reply #3 on:
September 08, 2021, 03:16:50 PM »
Bob can explain it quite well. If he doesn’t chime in, I’ll try to find one of the places he explains it.
Dave
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USA, OK, Stigler
Dave
Mr.P
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Real Name: Marco
Re: valve question
«
Reply #4 on:
September 08, 2021, 03:33:32 PM »
“ It is a crazy interesting animal, that once you learn how it works and gain control of it can turn the airforce guns from mild mannered to and absolute beast.”
Nice line, sums it up perfectly.
I have experimented widely with hammers and springs and tanks and even different custom valves.
If you want to keep it simple and you don’t have a chronograph, most people get the most consistent shooting a few hundred psi below 3000. When the pressure is very high on these valves, they need a little bit of extra force to knock open.
So when the tank is filled 3000 psi, you will find that you have to increase the “power wheel” (hammer-spring tightness) to get the same energy as you would get at 2700 psi with a lower power wheel setting.
In fact if you fill to 3000 psi and leave the Power wheel alone, you will notice your velocities and energy steadily increase as the tank pressure drops to whatever your gun’s “sweet spot” happens to be (This will be a little bit different for each gun I forget what most people find to be the typical sweet spot pressure). Once you get past the sweet spot, speed and energy will start to decline as the tank pressure drops lower and lower.
So what some folks do is get a chronograph, pick a power wheel setting and pick a projectile, fill it all the way up to 3000 and just shoot until the pressure is not producing adequate speed. For each shot, record the velocity in the tank pressure. You can look over these numbers in whatever way works best for your mind. You can make a little graph and look at the fill pressure where you either had the most consistent string of shots or the particular shot characteristic you’re looking for.
All of this is assuming that you were shooting the same projectile at the same power wheel setting.
The power wheel can increase the energy of the hammer strike. I’ve done a lot of shooting with my Air Force guns and I know how to shoot a reasonably flat string just by making small adjustments to the power wheel as i shoot.
As stated earlier, the weight of your projectile also has a noticeable effect on how the gun shoots. A heavier projectile will result in the valve staying open longer because it plugs the barrel and the back pressure ends up creating more dwelltime. I first noticed this before I had a chronograph because my TalonP was much louder with heavy than with light projectiles. A chronograph confirmed that the velocities of heavy and light pellets were much closer than I would’ve ever expected them to be. Turns out that extra dwelltime just about makes up for the extra weight and so you get shots with surprisingly similar velocities but much higher energy when you put a heavier projectile in the gun.
Another interesting thing which should only be approach with caution: if you get a tank capable of higher fill pressures, You can get a crazy amount of energy out of these guns. The problem is you will need a custom made valve stem, something that handle the higher hammer strikes needed to knock the valve back at higher pressures, and a heavy spring and hammer to create enough dwell time. Apparently the stock valve stems can fold / bend under these kinds of conditions.
I got a couple of custom valves that have very durable stems and I can get what feels like pretty outrageous power.
«
Last Edit: September 08, 2021, 03:38:17 PM by Mr.P
»
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USA, NY
All kinds of shooting is fun… I don’t care if it’s a gun, if it’s got a trigger on it it’s fun.
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rsterne
Member 2000+fps Club
Bob and Lloyd
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Posts: 26958
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Real Name: Bob
Re: valve question
«
Reply #5 on:
September 08, 2021, 04:42:27 PM »
Nope, not a balanced valve, but it does "blow open" to some degree, and depending on the SD of the projectile and how the hammer spring are adjusted, it can stay open and dump the tank.... Here is a diagram showing how the forces cancel each other to some degree when the valve is open....
When the valve is closed, however, there is full closing force on the poppet (area times pressure), and no "balancing force" to reduce the hammer strike to crack the valve.... That is why I say it is not a balanced design....
When the valve is open, the difference in area (shown in red) between the OD of the top hat and the ID of the valve bore (the OD of the stem) creates a force that helps to keep the valve open and increases the dwell.... The higher the breech pressure (heavy for caliber pellet, ie high SD, which is slower to accelerate), and the larger the top hat compared to the valve stem diameter, the more force available to open the valve.... Taken to the extreme, as the tank pressure drops, the valve can remain open and dump the entire tank contents in a single shot.... If the bore is small, relative to the top hat OD, that also increases the breech pressure after the pellet has exited the muzzle, increasing the likelihood of a tank dump....
If you want some practical examples of Condor tuning, my thread on the .257 Condor should help....
https://www.gatewaytoairguns.org/GTA/index.php?topic=165836.
Bob
«
Last Edit: September 08, 2021, 04:45:59 PM by rsterne
»
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Rob M
GTA Senior Contributor
Posts: 6308
Re: valve question
«
Reply #6 on:
September 08, 2021, 05:37:00 PM »
another thing to note james, there are some cheap imitation condor valves on ebay if you dont wanna start from scratch.
https://www.ebay.com/itm/293804214464?hash=item44681888c0:g:HMkAAOSw05JfmWYV
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Louisiana
sb327
Expert
Posts: 1790
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Real Name: David
Re: valve question
«
Reply #7 on:
September 08, 2021, 07:53:23 PM »
Thanks Bob.
I have made a valve that acts quite similar to the conventional ‘balanced valve’. It doesn’t take near the strike to open as the same size conventional Airforce valve. I have not really tested it for tuning ability, it was just a ‘proof of concept’ idea I had. I think it would be best suited for higher power applications. Details of it are in my condor thread.
Dave
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USA, OK, Stigler
Dave
JPSAXNC
Sharp Shooter
Posts: 508
yes
Real Name: James
Re: valve question
«
Reply #8 on:
September 09, 2021, 08:36:58 AM »
Thanks for the replies. Would it be possible to modify the valve so that it didn't stay open with increased breech pressure? TIA
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USA, North Carolina, Saxapahaw
rsterne
Member 2000+fps Club
Bob and Lloyd
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Posts: 26958
GTA Forums Person of the Year 2017
Real Name: Bob
Re: valve question
«
Reply #9 on:
September 10, 2021, 01:15:50 AM »
Actually, in my experience, the lower the pressure in the tank the more likely the valve is to stay open and dump.... When the tank is full, the air flowing past the poppet, and through the ports behind the poppet and into the stem, causing the closing force mentioned in the diagram above.... Think of them as "drag" forces from the air flowing, adding more closing force.... a "sail" installed in a conventional PCP valve does the same thing.... As the tank pressure drops, that force reduces, and the "blow open" force from the top hat can take over, particularly if you have a heavy bullet....
In a stock Air Force valve, the port behind the poppet, leading into the hole in the stem, is a single through hole at 90 degrees to the stem, and as such presents lots of corners for the air to turn through, and lots of drag.... When I angled those ports to streamline the flow, it was more difficult to get a bell-curve, and the valve required less hammer strike for a given dwell.... My .257 Condor thread explains all that.... I did not have a tank dump, but I am pretty sure that streamlining those ports increases the likelihood of it occurring....
If, on the other hand, you increase the OD of the valve stem, you decrease the difference in area to the top hat, and reduce the "blow open" effect.... If the stem equals the top hat diameter, it is eliminated completely, and you will need a much heavier hammer strike to get sufficient dwell.... Doug Noble's highest performance valves require both a heavier hammer and spring to maximize the power.... but have an extremely light valve spring....
Bob
«
Last Edit: September 10, 2021, 01:28:44 AM by rsterne
»
Logged
Coalmont, BC, Canada
🇺🇦
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
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valve question