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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"
Simplified Balanced Valve
PikeP:
Is my 25 gram hammer light, or wait, is it heavy? Guess that depends who/what you ask, yourself, a scale or the valve which the hammer functions in...
My current hammer weight in my 60% balanced valve is objectively heavy, it only needs 3.5 lbs of spring @ 25 grams to make 40 fpe, where as I needed 7 lbs of spring and 50 grams of hammer in my conventional valve to produce equal power.
While many may think subjectively, oh a 25 gram hammer making 40-60 fpe is light, its not when your valve is held closed with 55 lbs, whereas in a conventional valve it certainly is very light...
So, am I running a light hammer, or a heavy hammer? Its gotta be one way or another....
Just more food for thought. Seems relative.
rsterne:
You made a blanket statement, and I provided the counter-argument.... Hammer energy produces lift, while hammer momentum produces dwell, in a conventional knock-open valve.... Period.... The hammer energy is produced by the spring (average force times travel) and while the hammer velocity changes with weight, the energy does not.... If you change the hammer weight, for the same energy the momentum IS changed, however (heavier hammer more momentum, and vice versa).... Therefore, the relationship between energy and momentum changes as you change the hammer weight....
Note, this only applies if the poppet travel is not artificially limited in some way, and all of the RESIDUAL hammer energy and momentum is not wasted by hitting the back of the valve (or the poppet hitting a stop).... The residual energy, of course, is the energy remaining after the valve cracks from the seat, which removes part of the energy (and momentum) by slowing the hammer.... These relationships are also affected by the closing force on the popper, which is spring force, plus poppet drag (pressure differential across it), and in a balanced valve, any net force provided by the balance chamber.... Again, the relationship between hammer weight and momentum (and hence dwell) for a given hammer energy, is simply dictated by physics.... I presume you are not suggesting those laws are wrong?.... As an aside, don't forget that flow through the valve reaches a limit when the lift equals 1/4 of the diameter, caused by the curtain effect.... Therefore, adding lift after that doees not increase flow.... This occurs at 1/16" lift on a 1/4" throat....
There is no question that the balance chamber in a semi-balanced valve can be made to do virtually anything you want it to.... from blowing the poppet open and dumping the reservoir, to only reducing the cracking force on the poppet, and anything in between.... Before you get all riled up, it would perhaps help to take a deep breath and look at what YOU said, and my response.... Believe it or not, sometimes we can both be right, and a pi$$ing contest is not necessary.... Your experiments are valued, and help all of us understand the complicated dynamics of semi-balance valves.... Let's not lose sight of that, please....
Bob
PikeP:
--- Quote from: rsterne on April 16, 2023, 06:46:44 PM ---You made a blanket statement, and I provided the counter-argument.... Hammer energy produces lift, while hammer momentum produces dwell, in a conventional knock-open valve.... Period.... The hammer energy is produced by the spring (average force times travel) and while the hammer velocity changes with weight, the energy does not.... If you change the hammer weight, for the same energy the momentum IS changed, however (heavier hammer more momentum, and vice versa).... Therefore, the relationship between energy and momentum changes as you change the hammer weight....
Note, this only applies if the poppet travel is not artificially limited in some way, and all of the RESIDUAL hammer energy and momentum is not wasted by hitting the back of the valve (or the poppet hitting a stop).... The residual energy, of course, is the energy remaining after the valve cracks from the seat, which removes part of the energy (and momentum) by slowing the hammer.... These relationships are also affected by the closing force on the popper, which is spring force, plus poppet drag (pressure differential across it), and in a balanced valve, any net force provided by the balance chamber.... Again, the relationship between hammer weight and momentum (and hence dwell) for a given hammer energy, is simply dictated by physics.... I presume you are not suggesting those laws are wrong?.... As an aside, don't forget that flow through the valve reaches a limit when the lift equals 1/4 of the diameter, caused by the curtain effect.... Therefore, adding lift after that doees not increase flow.... This occurs at 1/16" lift on a 1/4" throat....
There is no question that the balance chamber in a semi-balanced valve can be made to do virtually anything you want it to.... from blowing the poppet open and dumping the reservoir, to only reducing the cracking force on the poppet, and anything in between.... Before you get all riled up, it would perhaps help to take a deep breath and look at what YOU said, and my response.... Believe it or not, sometimes we can both be right, and a pi$$ing contest is not necessary.... Your experiments are valued, and help all of us understand the complicated dynamics of semi-balance valves.... Let's not lose sight of that, please....
Bob
--- End quote ---
There was no blanket statement. Keep your emotions and personal feelings out of it, there is also no ^*%$#@ contest except the one you create yourself. I stated there is no substantial change in lift / dwell when altering your hammer weight and spring within a specific range of 50%-100% (the range I have been able to personally test) to retain identical power output, what is blanket about that? Wheres the fallacy?
If you have such an issue with my so called blanket statement that this relationship does not change significantly, and as you say, it's simply physics, I kindly await the formulation of math or data to concretely disprove it.
-Matt
rsterne:
Thank you for destroying a very valuable thread with your rant.... >:(.... I see that your "Watched" label is still required, something I will be requesting....
I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, and the relationship between hammer mass and momentum is well documented.... With a conventional valve, if you lighten the hammer (less dwell), you must increase the energy (more spring force and/or travel) to compensate and keep the FPE (area under the lift/dwell curve) unchanged.... The opposite also applies, a heavy hammer can deliver the same FPE with less energy (lift).... The Physics comes into the basic understandings of lift being proportional to energy, while dwell is proportional to momentum (once the energy to crack the valve is subtracted).... As I tried to explain, the flow through the valve, if opened more than 1/4 of its diameter, no longer increases with lift, so for a valve that is ACTUALLY opening that far (easy to measure, but also quite rare in an efficient PCP), all you are left with to change the FPE is a change in dwell with hammer momentum, be that achieved by mass or spring energy.... Just because you happen to disagree is no reason for the rest of us to throw out that valuable piece of information.... or a reason to rant....
While there may be certain valve configurations (balanced, semi-balanced, operating with a hammer or poppet stop, etc.) where the lift does not change (because it cannot), the lack of relationship between lift and dwell as you change hammer mass is caused by those other factors, and your statement, if applied only to those situation, may well be correct.... There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....
Bob
PikeP:
--- Quote from: rsterne on April 17, 2023, 02:34:30 PM ---Thank you for destroying a very valuable thread with your rant.... >:(.... I see that your "Watched" label is still required, something I will be requesting....
I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, and the relationship between hammer mass and momentum is well documented.... With a conventional valve, if you lighten the hammer (less dwell), you must increase the energy (more spring force and/or travel) to compensate and keep the FPE (area under the lift/dwell curve) unchanged.... The opposite also applies, a heavy hammer can deliver the same FPE with less energy (lift).... The Physics comes into the basic understandings of lift being proportional to energy, while dwell is proportional to momentum (once the energy to crack the valve is subtracted).... As I tried to explain, the flow through the valve, if opened more than 1/4 of its diameter, no longer increases with lift, so for a valve that is ACTUALLY opening that far (easy to measure, but also quite rare in an efficient PCP), all you are left with to change the FPE is a change in dwell with hammer momentum, be that achieved by mass or spring energy.... Just because you happen to disagree is no reason for the rest of us to throw out that valuable piece of information.... or a reason to rant....
While there may be certain valve configurations (balanced, semi-balanced, operating with a hammer or poppet stop, etc.) where the lift does not change (because it cannot), the lack of relationship between lift and dwell as you change hammer mass is caused by those other factors, and your statement, if applied only to those situation, may well be correct.... There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....
Bob
--- End quote ---
I see no formula, nor data sets here to prove that when altering your hammer weight by 50-100% and spring rating in a manner to retain the same power output, that the relationship between lift and dwell changes significantly. This is a contribution to this thread, as lift plays a large part in a balanced valves chambers height requirements.
Thanks,
-Matt
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