Makes perfect sense ... and no matter at this point being all my PCP's with balanced valves have reduced area tapered throat transfer tubes in them.
It really upped the efficiency and chopped the muzzle report doing so.
I'm following your balanced valve threads closely. I'm on a crash course to learn about higher energy PCP airguns. and apply some engineering principles as well.engineering
My thinking on choked flow fits right in with the data that you provided in this instance.
Calculated Mach number:
Mcalculated=(Vpellet/Vsos)x(caliber^2)/TPORT^2
In real life, that actual flow cannot exceed Mach 1.
If Mcalculated > 1, then flow MIGHT be choked. You can increase the transfer port size and you MIGHT get an increase in velocity.
If Mcalculated <= 1, then the flow is NOT choked. There is nothing to be gained by increasing the port size.
For 2200psi air, SpeedOfSound (Vsos) is about 1250fps. Caliber is 0.218 so:
TPORT=.250" @ 940 fps, Mcalculated=0.57, choke=FALSE
TPORT=.210" @ 980 fps, Mcalculated=0.84, choke=FALSE
TPORT=.175" @ 980 fps, Mcalculated=1.22, choke=TRUE
TPORT=.160" @ 960 fps, Mcalculated=1.43, choke=TRUE
TPORT=.140" @ 915 fps, Mcalculated=1.77, choke=TRUE
To eliminate choking, here's the smallest port size (so that Mcalculated = 1):
TPORT = sqrt((Vpellet/Vsos)x(caliber^2))
sqrt((980/1250)x(0.218^2)) = 0.193"
A 0.193" transfer port is likely to yield the best velocity (if that were your only goal) with this configuration. Maybe 985fps.
If I'm going for better efficiency, and I have sufficient barrel_length to achieve my desired velocity, then I do want some choking of the flow. Once flow is choked, further projectile acceleration comes from gas expansion. Expanding the air in a long barrel squeezes out more energy, instead of dumping it out the muzzle while still under high pressure.
I've been playing with your valve design (thank you), and my project is slowly progressing. I've tested a few aspects of it, but It might be a few/couple weeks before I can actually shoot a complete assembled gun:
Benjamin Armada (new)
.22 caliber (0.218)
balanced valve (Motorhead)
0.45L 4500psi bottle
2000-3000psi reg pressure (have not decided yet)
33gram solenoid actuated hammer (electronic)
80fpe max (maybe 100fpe later)
I had done some experiments with an electronic hammer a few years ago. It worked well, but I decided that it was not worth the complexity in the 12fpe gun that I was using it on.
This project will be a higher energy bench gun, so I'm revisiting an electronic hammer design.
The electronic hammer should give me better control over the valve dwell. I'm designing a system that will have four settings. 20fpe (light pellets), 40fpe (18.1gr), 60fpe (25.29gr), and 80fpe (34gr).
Once I get the power plant working to my liking, I'll swap out the stock barrel for a longer (700mm) custom barrel.
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