ADVANCED TUNING for the JSAR Raptors as well SS-2 Balanced Valves

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.

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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.

so what are the chances of getting a balanced valve for mrod these days ?

Hope this is not out of line ... cross forum postings.

This subject has been more active over on the GTA, but of late the thinkers and doers have been hiding out and not real active. So with some further interest in these type valves happening here I'll share what the evolution has been in my testing R&D. * The Tuning dynamics remain the same best I've found.

SEE: https://www.gatewaytoairguns.org/GTA/index.php?topic=167384.msg155875265#msg155875265



In this configuration am finding out that some others who are also building these type valves that EXTERNAL springs in Very High Output applications can be troublesome with coils getting dragged by the airflow leaving containment fouling the valve mechanics. Extreme but read some reports .. An FYI.

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That's an interesting problem. I have thought about similar drag issues that might affect valve dwell and general performance issues in other valve systems, but this problem brings a complex design that I had in my head for relocating a valve spring aft towards the hammer and creating an adjustable length pin for stroke tuning . Hard to describe, but the best that I can do right this sec from my phone is an ASCII diagram:



Hammer > []===|WWW||---D



The || part to the right of the spring (WWW) is a fixed point in the housing (or block). The initial idea that I had was that the strike point on the pin ([]--|) would be detachable (threaded) and would be the adjustment point. I thought about it a little more and came up with some ideas that sat better with me, where it would be a free-floating piece that turns the stem into a pin guide with a weak return spring to keep it near the hammer at rest. I also pondered the idea of relocating the threads towards to the poppet itself, but I don't necessarily like the idea of threading any of it.



That's about as far as I got with the mental blueprint though 

Hey Scott,

Do you see a possible variance with this as you get into larger calibers and heavier slugs? My Raptor .357 hits a wall just over 200 fpe with 3500psi reg, I have micro adjusted everything that I can and keep getting the same outcome, but noticed that the valve port and transfer port are .31 and the breech port and barrel port are .25. Do you think the heavier and larger slug may deviate from what you are seeing in the smaller calibers and port size since it is pushing the envelope for the design? JSAR posted a vid of them getting 295 FPE with the Raptor .357 but I am guessing that is unregulated and with larger ports but not sure and I am not able to get an answer from them on that. I am not sure if they happened to be testing that when you were helping out there, but hopeful you might have some insight for me? Was wondering about spring tension in the valve also? 

Thanks,

Travis