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|04-20-2011, 12:40 AM||#1 (permalink)|
Join Date: Oct 2007
Location: Plattsburgh, NY
Closed bolt spool valve - Ion conversion and group project
Over the past few years I've been working on a conversion to turn an Ion into a high efficiency closed bolt gun. Bought my first "broken" Ion on PBN almost 4 years ago for $55 for the project. Had a working prototype shortly after that, and have made a dozen or so changes to the system since then. Wrapped up the most recent generation the other day.
The valve operates similarly to the unreleased Legion Shocker (prototype 03 Shocker), but with a normally open valve that vents to fire instead of a normally closed valve that pressurizes to fire. Nice clean air path, minimal gas expansion, very fast opening valve. Piston lets the dump chamber fill when it moves forward, isolates it on the rearward stroke. Lets the system be shot mechanically or electronically.
First generation, I threaded the back end of the firing can where the hex portion is. Let me use a female coupling and have a rear plug that was threaded so I could adjust how far back the firing piston moved with each shot. Worked great, but never would have been field legal because you could very easily adjust the velocity with no tools.
I was so excited to use it, I never even cleaned the layout dye off of the parts. They are still blue, and probably always will be.
Preliminary testing was crappy on the efficiency end - until I chronoed it and realized that I was shooting nearly 400 FPS. Once I brought it down to about 290, I was getting early results of almost 2,300 shots from a 20 ounce. Needless to say, I was pretty enthused given that this was the first prototype, and it worked the first time I aired it up (shooting it with a plugged cocker 4-way actuated with a pair of pliers).
Sat on the design for over a year trying to decide what to do with it - patent it, release it openly, or keep it to myself. Finally started sharing information about it after deciding to just release it openly. Patents are only worth it if you have the money to defend them, and given the mechanical shortcoming of the design - a limited max rate of fire - I figured it was for a niche market of people wanting efficiency above all else, and that shopping it to companies who would want the patent would probably be a waste of my time.
Did quite a bit of design work to it over that year. Figuring out a way to hold the rear plug in without having to thread the back end of the can was one of the more pressing concerns in the design. I also needed an easier to machine way of stopping the piston's forward travel. The original version had 2 steps in the bore of the power tube - one to make the seal, one for the piston to butt up against to keep it in place.
I ended up coming up with this:
The power tube was changed to aluminum for dimensional stability as I had an easier time holding tolerances with aluminum than with Delrin. The larger diameter aluminum piece fit over the hex portion of the firing can, and was held in place with some set screws that dug into the flats on the hex. Seemed to work alright for me, but both of my testers had it come flying off during testing because their set screws were not tight enough. The piston travel length was no longer adjustable, it was now permanently set to travel as far as possible - velocity was now adjustable only via pressure or shimming the gap between the piston and the plug, both acceptable for field use.
Another half dozen variations, at least one going back to the older method of stopping the piston forward travel as I had made a digital readout for the tailstock on my lathe, and drilling to accurate depths was no longer problematic. Sadly, these all looked close enough that I never took pics of the intermediate steps before sending them to testers.
I decided to try a version without a power tube. It worked on the same basic principle - piston goes forward, chamber pressurizes, bolt goes forward. Air behind piston vents, piston retracts, chamber dumps, bolt retracts. Wash, rinse, repeat. This version works very similarly to Thorpydo's plunger prototype if you are familiar with that one. A neat feature that I want to mess with more in the future is that since the bolt makes the seal itself, the chamber is self regulating in that when the bolt begins to retract, it can trap some chamber pressure to help boost efficiency.
My turning had gotten better over time, my milling - obviously not as much.
At one point between the tubeless version and now, I made the bolt thinner. This allowed the powertube to grow, subsequently allowing for a larger bore through it and improved flow. The thinner bolt also created a longer delay in the firing cycle before the bolt began moving forward again - this made it much more reliable shooting without a force feed hopper, which had been pretty much necessary before. The thinner bolt has stayed through current versions.
About 2 weeks ago, I began the most recent version. I had integrated the piece that held the rear plug in with the donut, replacing the entire back end. Originally, this was just held on with the rear frame screw - potentially problematic.
Obviously, I made the move back to Delrin for the powertube. My plastic turning had improved dramatically, and it provides a small amount of cushion or the piston, preventing the tip from deforming - a problem I had in my mechanical Aedes which uses a near identical valve, just in a lower tube. They are also way faster to machine.
I thought I had finished the newest version this past weekend when I had an epiphany while trying to fall back to sleep Sunday morning (works in an Epiphany too). If I add a groove to the inside of the donut, and notch out part of the back end, I can keep the c-clip that holds the regular donut on. This lets it be tested and used without a frame, and is quite a bit safer. So into the shop I went, and came out with this:
You can see where the set screws from the old retainer piece dug into the can.
I'm out of HPA to test and the local place isn't filling yet, but doing testing with CO2 and air from a shop compressor, the system is running about 110psi to get to 290FPS, which equates to about 2,100 shots from a 68/45 (sealed dump chamber of a known volume makes efficiency estimates easy when you know the pressure). A little lower than earlier versions, but I'm pretty sure I can tweak it back to a little more efficient than it is.
Best $55 broken gun I've ever bought
At one point since making the project public knowledge, I offered the design up as the basis for an open source group project here on MCB. It is currently in the prototyping stages as a complete gun, not a retrofit. If anybody is interested in the project in any way, stop by the thread in the custom guns section.
|04-20-2011, 02:30 PM||#3 (permalink)|
Join Date: Oct 2007
Location: Plattsburgh, NY
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