Scott, how are you calculating the maximum mass flow rate?.... During a discussion in another thread we multiplied the air density at the pressure (kg/m^3) used by the orifice area (m^2) times the speed of sound at that pressure (m/s) to get the maximum mass flow rate (in kg/s).... This was then derated about 5-10% to allow for losses.... You can use the calculator I linked to above for the speed of sound and air density.... http://www.wolframalpha.com/widgets/view.jsp?id=b63c87b0a41016ad29313f0d7393cee8/For example, at 4000 psi and 20*C, we get Mach 1 of 451.1 m/s and a density of 302.7 kg/m^3.... for an orifice of 1 cm, we get....451.1 x 302.7 x 1 x PI/4 / 100 / 100 = 10.72 kg/sec.... which is 10.72 grams/mSec.... or 165.4 grains/mSec.... less a derating factor of course.... 150 gr/mSec seems about right....The only way to increase the mass flow at that temperature is to increase the inlet pressure, it is completely independent of outlet pressure.... In addition one of the conditions for choked flow is a pressure drop of 47% across the choke.... Here is the discussion, if you haven't gone through it yet.... Jim_Hbar's Post #69 is particularly revealing.... http://www.gatewaytoairguns.org/GTA/index.php?topic=66737.60How does that compare to what you are doing?....Bob

Scott, what I have done is to put the density and speed of sound, from the online calculators, into a spreadsheet, using pressures up to 6000 psi, and then used Excel to generate a trendline for each.... This equation is then used to calculate the density and Mach 1 from the pressure for ANY pressure <= 6000 psi.... It is what Lloyd is using for his new spreadsheet with the VanDerWaals corrections.... In the spreadsheet I have the trendline equations for air, Helium, and Nitrogen, and I will send you a copy of the same one I sent to Lloyd.... All the data is at 20*C.... Lloyd hasn't added a column for maximum Mass Flow yet, but once you have the Density and Mach 1 for each Pressure increment it's just one more column.... If there are no restrictions, the orifice ends up being the bore diameter.... Bob

Loyd,.................................................Imbalance needs to be designed such that the pilot stage is enough to accelerate the valve sufficient for ACCEPTIBLE speeds. As you can see this is a dead end-the lighter the projectile the larger the imbalance needs to be. Start by figuring out what the weight of the pellet will be."Easy to open..... difficult to close" Man ....you have no idea:)Also, you mentioned that paintball marker have similar valves. Would you mind pointing me in that direction? Or is there a name for it that i can google?