Tuning Tuning a Balanced Valve — for quieter shots

Tuning a Balanced Valve — for quieter shots​


In my ignorance I said:
Balanced valve = more power at lower reg pressures = BETTER! 😃

And promptly bought a PCP with a balanced valve.
(RTI Prophet II Compact Performance,
.25cal, 500mm RPB barrel)


Continuing in my ignorance, I had made a plan:
I was going to dial in a high reg pressure, and then dial the hammer spring far below the max. power at that reg pressure (as in 10% or 20% "below the knee").

Why? Because I wanted a very short sip of air — at a very high pressure — in order to quiet my shots.
(The resulting higher MV variations I was willing to accept, since my shots were going to be short range.)



⚙️ PLEASE, ⚙️
school me on tuning guns with balanced valves!!

I might not be able to tune my gun "quiet" as I was planning.
➠ But I certainly need to know how to tune it!


Thanks! 😊

Matthias
 
Hi mate, you are approaching your problem from the most complicated prospective. The main purposes of tuning are accuracy and efficiency. Now, let's draw our work-map:
-we need to know how powerful is, irl, our gun. If it can reach only a certain amount of energy, we can avoid to lose time and money on overweighted ammos
-we need to find a suitable round for our gun, considering weight and diameter. Doesn't matter if we are talking about slugs or pellets
-we need to find the speed ranges where the chosen ammo perform at its best
-we have to be sure that those speed ranges are reachable with our gun set-up

Now, and only now, we can start with the proper tune:
-set your reg at a random value (125b for example)
-turn the spring wheel all the way down ("-" mark)
-shoot 2-3 rounds and check their speed
-add 1-2 clicks on the spring wheel ("+" mark), shoot 2-3 rounds and check speed again
-when you will see a sudden improve in speed, you will know you opened the valve. That's it. Are speed and accuracy spot on? Great, you finished your work. Otherwise, change your reg pressure according to your needs: low it if your rounds are too fast, increase it if they are too slow. Reset the spring wheel and start again.
 
Agree here, tune for consistency and accuracy not for sound.

The lower the power the quieter the gun, I'm not sure if I'll try a high power tune but focus on the sound, this is the reason we have LCDs

But also I think you are into something here... an inefficient tune, where air is wasted have a different sound, not sure if its volume, but I can hear while I'm tuning when I'm wasting some air and while doing adjustments I can feel/hear when the tune is getting better.... The problem is that the more the power is reduced the lower the sound it will be so the best tuning point is not the lower in sound but when you find the balance with speed/accuracy and efficiency of your rifle.

Tuning a self balanced valve is almost like cheating although fine tuning it might be a bit difficult to master, the process is different of that of tuning a regular valve, to tune a balanced valve is to find the min amount of force that it's needed to just open it at the given regulator pressure, so with it you just have to really focus on what regulator pressure you want to use lower the hammer all the way until valve doesn't open anymore then gradually increase the HST until it opens and once you find that spot give it an extra 1/4 turn and you are good to go, the lower the quieter. The high pressure reg and short sip of air you mentioned I believe is what the balanced valve will do for you by it's design, but it's a common approach on the other regular valve, I least this what I understand and as usual I might be wrong and people can correct me here if that's the case. But this is how I approach my balanced valve tuning on my RTI. I think I did a video about the tuning.

Nice topic Matthias
 
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Agree here, tune for consistency and accuracy not for sound.

The lower the power the quieter the gun, I'm not sure if I'll try a high power tune but focus on the sound, this is the reason we have LCDs

But also I think you are into something here... an inefficient tune, where air is wasted have a different sound, not sure if its volume, but I can hear while I'm tuning when I'm wasting some air and while doing adjustments I can feel/hear when the tune is getting better.... The problem is that the more the power is reduced the lower the sound it will be so the best tuning point is not the lower in sound but when you find the balance with speed/accuracy and efficiency of your rifle.

Tuning a self balanced valve is almost like cheating although fine tuning it might be a bit difficult to master, the process is different of that of tuning a regular valve, to tune a valance valve is to find the min amount of force that it's needed to just open it at the given regulator pressure, so with it you just have to really focus on what regulator pressure you want to use lower the hammer all the way until valve doesn't open anymore then gradually increase the HST until it opens and once you find that spot give it an extra 1/4 turn and you are good to go, the lower the quieter. The high pressure reg and short sip of air you mentioned I believe is what the valanced valve will do for you by it's design, but it's a common approach on the other regular valve, I least this what I understand and as usual I might be wrong and people can correct me here if that's the case. But this is how I approach my valanced valve tuning on my RTI. I think I did a vídeo about the tuning.

Nice topic Matthias
Spot on. And yes you did a preview video about the new valve.
 
Since I woke too early and have some time, I’ll give you my advice, albeit not specific to the P2, Matthias. I do not think that there’s a valve spring adjustment here but if there is, start out fully open/least tension.

Start with the reg at a level that is likely to be lower than needed (say 90bar) and follow manufacturers guidelines with regard to degassing (if needed) when adjusting the reg. Typically degassing is needed to reduce pressure (at the outset). Increasing pressure in subsequent steps can be done without degassing, but you should check!

You are obviously aware that tuning on the downslope for high efficiency can have some drawbacks. The extent of those effects vary from one gun to another. In keeping with your goal of quiet operation, it’s worth noting that once you get to 5% below plateau speed, the gun should already be pretty quiet. It may not be advantageous in terms of noise to drop further down the curve, so I would first aim for a target speed that is 5% below plateau. You will get a sense of sound in relation to the curve as you tune and can adjust the target as you see fit. One issue with tuning below the knee is that projectile speed will tend to follow tank pressure. Regulators are imperfect and tend to run higher at full tank and vice versa. The optimal tune (at -2 to -4% below plateau) buffers that effect and therefore losing that buffering is a side effect of what you’re planning to do. Therefore, I recommend doing your tuning at median tank pressure. For example, if your max fill is 250 and reg ends up at 125, do your tuning at 190bar, either tethered or by keeping it in that range (210-170). Otherwise you can end up with a gun that shoots too fast or slow at one end of the spectrum because you tuned at the other end. Onto the process.

At starting (low) reg pressure and low hammer, run 3 shots over the chrony and incrementally increase hammer and repeat. Velocity will increase with hammer until you get to the plateau speed for that particular pressure. As you approach it the gun will get louder due to wasting air.

Determine if that plateau speed -5% is what you’re looking for. If not, increase/decrease the reg pressure by 5-10bar (depending how far off) and repeat the process. Since increased hammer is needed for increased pressure, you don’t have to go back to minimum hammer to find the plateau after increasing the reg - just back it off a bit to find the new plateau.

The goal is to find the pressure and hammer setting at which you get your target speed at plateau speed -5%. You should now have a sense if that 5% drop is sufficiently quiet for your needs. As you dial it in, take more shots to determine how stable the speeds are and try to do that at the median tank pressure.

Once you’re set at plateau-5%=target speed, fill the tank to your intended max working pressure and test the speed to see how much it perturbs. Then do the same at a pressure of 20-30bar above the reg set point. Is the deviation acceptable? If not then you have to go closer to the plateau speed.

Finally, if there is a valve spring adjustment to fine tune dwell, you can increase its tension progressively while checking speed until it just begins to reduce speed. In addition to make things a little quieter, it can buffer the effects of variance from the changing tank pressure as you shoot.

Hope that helps.
 
Since I woke too early and have some time, I’ll give you my advice, albeit not specific to the P2, Matthias. I do not think that there’s a valve spring adjustment here but if there is, start out fully open/least tension.

Start with the reg at a level that is likely to be lower than needed (say 90bar) and follow manufacturers guidelines with regard to degassing (if needed) when adjusting the reg. Typically degassing is needed to reduce pressure (at the outset). Increasing pressure in subsequent steps can be done without degassing, but you should check!

You are obviously aware that tuning on the downslope for high efficiency can have some drawbacks. The extent of those effects vary from one gun to another. In keeping with your goal of quiet operation, it’s worth noting that once you get to 5% below plateau speed, the gun should already be pretty quiet. It may not be advantageous in terms of noise to drop further down the curve, so I would first aim for a target speed that is 5% below plateau. You will get a sense of sound in relation to the curve as you tune and can adjust the target as you see fit. One issue with tuning below the knee is that projectile speed will tend to follow tank pressure. Regulators are imperfect and tend to run higher at full tank and vice versa. The optimal tune (at -2 to -4% below plateau) buffers that effect and therefore losing that buffering is a side effect of what you’re planning to do. Therefore, I recommend doing your tuning at median tank pressure. For example, if your max fill is 250 and reg ends up at 125, do your tuning at 190bar, either tethered or by keeping it in that range (210-170). Otherwise you can end up with a gun that shoots too fast or slow at one end of the spectrum because you tuned at the other end. Onto the process.

At starting (low) reg pressure and low hammer, run 3 shots over the chrony and incrementally increase hammer and repeat. Velocity will increase with hammer until you get to the plateau speed for that particular pressure. As you approach it the gun will get louder due to wasting air.

Determine if that plateau speed -5% is what you’re looking for. If not, increase/decrease the reg pressure by 5-10bar (depending how far off) and repeat the process. Since increased hammer is needed for increased pressure, you don’t have to go back to minimum hammer to find the plateau after increasing the reg - just back it off a bit to find the new plateau.

The goal is to find the pressure and hammer setting at which you get your target speed at plateau speed -5%. You should now have a sense if that 5% drop is sufficiently quiet for your needs. As you dial it in, take more shots to determine how stable the speeds are and try to do that at the median tank pressure.

Once you’re set at plateau-5%=target speed, fill the tank to your intended max working pressure and test the speed to see how much it perturbs. Then do the same at a pressure of 20-30bar above the reg set point. Is the deviation acceptable? If not then you have to go closer to the plateau speed.

Finally, if there is a valve spring adjustment to fine tune dwell, you can increase its tension progressively while checking speed until it just begins to reduce speed. In addition to make things a little quieter, it can buffer the effects of variance from the changing tank pressure as you shoot.

Hope that helps.
Great
 
Hi Matthias, I just wanted to comment on one of the points in your original post:
In my ignorance I said:
Balanced valve = more power at lower reg pressures = BETTER! 😃

A balanced valve does not produce more power at lower pressure. A balanced valve is simply easier to knock open…easier to develop a given amount lift and dwell with a lighter hammer and/or spring. This advantage comes at a price, however. Relative to a conventional valve, balanced valves are more sensitive to inevitable variations in hammer strike, more sensitive to pressure variations related to regulator linearity and temperatures changes, and more susceptible to a slow first shot due to O-ring stiction (breakaway friction of the O-ring which seals the balance chamber).

As such, I am of the opinion that a balanced valve is best suited for energy levels somewhere north of 100fpe. In that role, they really shine. For everything else, a conventional valve is hard to beat for its simplicity, tuneability, reliability, and consistency.
 
Hi Matthias, I just wanted to comment on one of the points in your original post:


A balanced valve does not produce more power at lower pressure. A balanced valve is simply easier to knock open…easier to develop a given amount lift and dwell with a lighter hammer and/or spring. This advantage comes at a price, however. Relative to a conventional valve, balanced valves are more sensitive to inevitable variations in hammer strike, more sensitive to pressure variations related to regulator linearity and temperatures changes, and more susceptible to a slow first shot due to O-ring stiction (breakaway friction of the O-ring which seals the balance chamber).

As such, I am of the opinion that a balanced valve is best suited for energy levels somewhere north of 100fpe. In that role, they really shine. For everything else, a conventional valve is hard to beat for its simplicity, tuneability, reliability, and consistency.
True, and they are also more sensitive to weather conditions than classic valve
 
To date my experience with balanced valves done by European manufactures is somewhat limited, tho seen and played with a few attempting to find a way in tuning them.
Here Domestically working with the JSAR inspired balanced valves I have massive amounts of R&D experience with them ;)

In designs that loosely follow the JSAR design the feedback pressure is a vented valve stem at throat to the chambers inner space. This pressure transfer from throat to chamber & speed / volume allowed is the miens valve poppet is pushed back to the seat. Can be small vented for longer dwell, larger vent speeds up the closing cycle.

It has been found that poppet LIFT is the best way to control run away dwell ( Aka: Buffered )
Also on these valves you can run a VERY STIFF poppet return spring as the effort to crack the valve open is so greatly reduced due to the area plenum pressure is working against being reduced.

You may wish to do a SEARCH using my name and term Balanced valve here on the AGN as well GTA forums. I have documented Lots & lots of design as well tuning / set up data on the subject.

And will note: Most balanced valve set ups Take only a modest to light hammer strike done by LIGHT hammers and many time short hammer stroke.
This is a minimum strike required to get poppet to snap open, and strike energy greater than this buys you little in performance, but major increases in air consumption. THESE VALVES are Pressure sensitive having the Speed Adjusting done via Regulator pressure and NOT hammer strike.
 
I’ve noticed some things that raised an eyebrow. What Motörhead and Nervoustrig said confirmed them. The poppet return spring is very stiff. The guns velocity is sensitive to tank pressure. I initially did not notice a slow first shot after sitting. I got one slightly faster shot. I just replaced my valve because I had a leaker. Built a .30 FX barrel for a trip I’m going on for the P2. When I get home today I will check the tune. I know what bar gets me the results I want. Now I have to check the hammer strike. You don’t want too much.
 
Ghost has it. Prophet 2 and 3. Jsar Raptor. I don't know if the M2-M3 Impact have it.
Most recent URGAN has one ...
FX has there own version, but it does not use pressure feedback to close, but adjustable poppet spring tension and lift limiter
 
Agree here, tune for consistency and accuracy not for sound.

The lower the power the quieter the gun, I'm not sure if I'll try a high power tune but focus on the sound, this is the reason we have LCDs

But also I think you are into something here... an inefficient tune, where air is wasted have a different sound, not sure if its volume, but I can hear while I'm tuning when I'm wasting some air and while doing adjustments I can feel/hear when the tune is getting better.... The problem is that the more the power is reduced the lower the sound it will be so the best tuning point is not the lower in sound but when you find the balance with speed/accuracy and efficiency of your rifle.

Tuning a self balanced valve is almost like cheating although fine tuning it might be a bit difficult to master, the process is different of that of tuning a regular valve, to tune a balanced valve is to find the min amount of force that it's needed to just open it at the given regulator pressure, so with it you just have to really focus on what regulator pressure you want to use lower the hammer all the way until valve doesn't open anymore then gradually increase the HST until it opens and once you find that spot give it an extra 1/4 turn and you are good to go, the lower the quieter. The high pressure reg and short sip of air you mentioned I believe is what the balanced valve will do for you by it's design, but it's a common approach on the other regular valve, I least this what I understand and as usual I might be wrong and people can correct me here if that's the case. But this is how I approach my balanced valve tuning on my RTI. I think I did a video about the tuning.

Nice topic Matthias
Fully agree with Orion! That's how I learned to tune my JSAR Raptor with it's balanced valve, small incremental adjustments go a long way with them.
 
Update. I knew I needed 125b to shoot a .30 pellet 880fps and a slug 870fps with the 500mm barrel. The gun was doing it so I started backing the HS out 1/4 at a time. Suddenly it shot 540fps. So I found where it went back to 880 then added a quarter turn. My gun had one full turn too much hammer spring tension. The gun feels and maybe sounds a little better. But I also know it could just be a PCP illusion because I twisted a screw. Most of you guys know what I’m talking about.
 
Update. I knew I needed 125b to shoot a .30 pellet 880fps and a slug 870fps with the 500mm barrel. The gun was doing it so I started backing the HS out 1/4 at a time. Suddenly it shot 540fps. So I found where it went back to 880 then added a quarter turn. My gun had one full turn too much hammer spring tension. The gun feels and maybe sounds a little better. But I also know it could just be a PCP illusion because I twisted a screw. Most of you guys know what I’m talking about.
Shoot the heck out of it and you will know ;)
 
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⭐ You guys are really great!
Thank you!! 😊

Very helpful explanations and comments. 👍🏼


➠ I get it when some of you mentioned "precision goes first — starting with quietness is the wrong order." —
However, for close range pesting I was going to change the order of my priorities a bit.... 😉
(And of course, 3" groups at 20y are not acceptable either....)


Matthias



PS:
For the thread readers that are interested in the video mentioned above by OriOn The Iguana Hunter, here's the link:
 
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