And thus begins my first intellectual contribution to Nerfhaven...
This easy mod will expand the capacitance of a hornet back-fire tank, customizable to as much volume as needed.
Ranges are dependent on your own pressure used, and how much you choose to expand the tank. Therefore, I won't be offering any review concerning ranges, but logically more discharge capacity can support a longer barrel, and provide more acceleration.
Part I: capacity expansion (holding pressure and firing)
Part II: output expansion (not holding pressure)
Part I materials required:
3/4” PVC threaded tee
3/4” threaded plug
PVC glue and primer (epoxy might also work, but the PVC glue is nice and gooey for filling gaps and air tight proven in my prototype)
3/4”x1/2” CPVC reducer (if you are using a CPVC barrel)
3/4” threaded nipple (optional if you want to expand it beyond what the plug will hold)
3/4” threaded cap (optional (to cap the nipple))
3/4” ball valve (very optional) (placing a valve midway down the nipple will create a third expansion usable mid war.
Part II requires a Bic pen (and cap)
3/8" drill bit (equal to a Bic pen cap outside diameter)
1" pipe clamp
(clamps and tape are to form a temporary seal for testing)
Heat gun (glorified hair dryer) or torch (preferably heat gun. Much more controlled) I got mine for 13$ new at Harbor Freight (a discount tool chain. Love that place!) probably 20$ish everywhere else.
Dremmel with spiral cutting bit, or drill press with 1/2” drill bit (preferably a Forestner type bit. It cuts a little more shallow)
Canned air/air compressor with spray nozzle
Less than an hour (+glue setting time)
Start by disassembling a hornet and getting to a bare tank. This is already covered in other posts, so I'll assume yourself capable of using the search function if you have questions.
Lop off one of the side legs of your tee level with the middle leg.
Here's the exploded view of what you'll be doing.
Insert your threaded plug to keep it from stretching out of round. (hand tighten to snug fit. You don't want to stretch the threads once it's heated)
Heat the PVC tee with a heat gun until it becomes shiny (it will be in a slightly mailable state)
Please don't burn yourself. Heat guns put off some serious heat.
Once it's shiny, stuff your hornet tank in through the leg you shortened until about 1/8” of the tank is sticking out the back. Re-heat and stuff your CPVC reducer into the barrel end (if you're using a CPVC barrel)
You can see how it's stretched and slightly deformed.
Allow to cool slightly, unscrew the plug and look to make sure the shoulder of the reducing section is past the hole of the the threaded leg.
Remove the tank and reducer. I had to use a rubber mallet. If it's really tight, re-heat then remove.
Fit test the tank and CPVC reducer into the tee once cooled. If every thing looks good, apply PVC primer to the inside of the tank (not the threads) and hornet tank. I realize it might not be the perfect chemical match for the plastic of the hornet tank, but we at least know it's appropriate for the PVC. Next apply PVC glue to both the tank and tee. Goop the heck out of it. We'll need it to be completely covered and air tight. Stuff the tank in, and rotate it 360 degrees to ensure the glue makes complete contact with all sides. Don't glue the reducer in. that will probably hold on it's own, and you may want to fill dead space later. Set it down with the plug pointing up and let it dry.
Once dry, remove the plug, and Dremmel out/drill out the shell of the hornet tank visible inside the threaded tee portion.
Don't drill any deeper than you absolutely need too. There is a peg with a piston on the end centered in the tank. You don't want to damage the rubber fitting on the end.
Be obsessive about cleaning out the shavings. Rinse it out with water, then use canned air or an air compressor to blow it out. Shoot air through a straw down the barrel nozzle. Get them all gone. Even one particle can hinder a seal.
Apply Teflon tape around the threads of your plug, and screw it in. You'll want a tighter than hand tight fit this time. (or until it stops leaking...)
Pump it up and test fire.
If you want more capacity than the plug holds, just screw in a nipple with a cap on the end.
If you want a mid-war expandable tank, just glue a ball valve in the middle of the nipple. Just slap on a coupled barrel extension to increase barrel length, and turn the valve to expand tank capacity to match, pump more and fire at an increased range.
Theoretically, you could create a hornet tank with more capacity than a titan if you wanted!
My incomplete airflow expansion: (Piston won't seal and hold pressure. Grrr.)
If you wanted to completely open the shell to try to enlarge the output nozzle for increased air flow, use a pipe cutter to gently get a channel set before applying pressure and cutting. This heat – stuff – glue method could be used to mate both halves back together. Though, I'm just e-taping, pipe clamping both halves together with a C clamp to hold both halves together laterally to test and trouble shoot. (E-tape and a pipe clamp didn't hold. the halves separated, and one half shot across the room. It took me 3 weeks to find the piston.) Don't glue it till you know it's capable of holding a seal. Mine still is not sealing. I drilled out the barrel side nipple, and epoxied a Bic pen cap in it's place the cap is too wide for the piston to seal on, but the cap lets you nest an adjustable Bic pen tube inside.)) If anyone else wants to give it a try, have at it. At the very least, I'm open to suggestions.
Pics of internals (because I haven't seen any on Nerfhaven)
barrel side peg, and supports partially drilled out to be replaced with Bic pen cap section at right.
cap being epoxied into place (pen tube inserted to help make sure it's going in squarely)
Taped and clamped for a test fire. (leaks out barrel. still a work in progress)
I haven't looked into it, but I've been wondering if the same heat – stuff - glue - drill method could be applied to increase the output capacity on a RF-20 piston...
Edited by shmmee, 30 October 2010 - 08:54 PM.