There is huge confusion when people start talking percentages in balanced valves, as there are three different ways to look at it.... I will use as an example the proportions I suggested in the drawing in Reply #546 on page 28 of the thread on simplified valves....https://www.gatewaytoairguns.org/GTA/index.php?topic=152413.540That valve had a balance chamber diameter of 2/3rd of the poppet seat diameter (66%)…. It reduced the cracking force of the valve by 44% of what it would be at the same pressure, without the balance chamber.... Here are the three ways to look at the percentages for that valve....Diameter of balance chamber compared to diameter of seat (in this case 66%)Reduction of cracking force (in this case 0.66^2, or 44%)Percent of original cracking force required to crack the balanced valve which is 100% - the % Reduction (in this case 100-44 = 56%)I'm not sure which percentage Travis uses when he is talking about his Gen2 SS Valve, but I think he means the diameters.... I realize he had played with a similar design previously, but he was very clear when I started the above thread on the simplified balanced valve that it would either blow open, machine-gun, or at the very least could never be tuned to produce a bell-curve.... I felt pretty good when I figured out how to make it work by increasing the diameter of the port in the stem, and decreasing the internal volume of the balance chamber to a minimum.... PikeP's spreadsheet was great, as it confirmed the direction I was going, and allowed us all to visualize what was happening and why that was the route to take.... It was also clear early on that the simplified valve, by eliminating an O-ring, solved the "stiction" problem of the Gen1 SS Valve....The smaller you make the balance chamber diameter, relative to the poppet, the less it reduces the hammer strike required to crack the valve, but the easier the valve is to tune by changing the hammer strike.... I gave a suggested range of DIAMETERS for the balance chamber of 60-75% of the seat, which results in a reduction in cracking force of 36-56%, or a resulting cracking force of 64-44% of the original force required.... I know that Travis is at the bottom of the range of balance chamber diameters (50-65%), because the valves he is producing are intended mainly for smaller calibers at medium power levels, and he is concerned about tunability.... My balance chambers tend to be larger than Travis' (66-71%), because in a big bore, your primary need is to reduce the hammer strike, and tunability is less important....The information, in great detail, both what worked and what didn't, is in the thread linked above.... What you decide on for a balance chamber diameter will depend on your use.... Also in that thread are details of failures where the small end of the poppet pulled apart at the O-ring groove, because there was simply not enough plastic between the bottom of the groove and the stem.... The ultimate (safest) solution is to use a one piece metal stem and poppet, particularly if your balance chamber is on the small side.... This requires a soft seat inside the valve body.... This is the solution used by JSAR in their Gen2 SS valve.... Bob
Yep, and if you shoot a regulated PCP, particularly with an adjustable regulator, you can use a larger balance chamber to reduce the hammer strike, and forget about the need for adjustability in the valve.... Operate it like a Cothran….Bob
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