2.5 inch QDV build

Technician1002 · Wed Oct 14, 2009 11:53 pm

Instead of waiting until I could post this in the showcase, I thought I would post this work in progress here open for comments. This build will take quite a while due to weather, budget, time, and other competing time obligations. This is a cannon on a budget.

This project is to up the power of my existing cannons. The t shirt cannon is built into a lightweight tank which is easily dented. I mostly use it with larger barrels. The tank is oversize for the smaller barrels and the valve is undersize for the larger barrels.

I am starting to get a collection of obsolete propane tanks that can not be legally refilled due to the new regulations on the OPD valves and triangle handles. POL valves are obsolete. The cost of changing the valve and getting a new certification is more than the cost of a new tank. ($30 valve installed + $20 for recertification) A $29.95 tank is cheaper.

I have been wanting a 3 inch valve, but the cost of the materials has been a limiting factor. I do have a piece of 2.5 inch UMHWPE on hand as well as some decent but rusty 2.5 inch pipe, so I am starting on a 2.5 inch valve in a 11 LB propane cylinder as a starting project. The large tank is reserved for the 3 inch QDV. I have a second one that will eventually become a 4 inch.

I have started by gathering supplies and cutting the pipe and tank. As I progress, I'll add to this thread. Enjoy. Comments are welcome. So far all the materials except the tools was obtained FREE.

MountainousDew · Thu Oct 15, 2009 4:54 pm

Rawr!
I see a monster spud gun in your future...
Can't wait to see "Frankenstein" in action.

Thu Oct 15, 2009 4:59 pm

Wow..I think the benefits of your type of valve will be evident at these dimensions...

What pressure will it use?

Moonbogg · Thu Oct 15, 2009 5:24 pm

This is going to be mighty.

Technician1002 · Thu Oct 15, 2009 6:14 pm

I made some progress today. The items done today were the removal of the handle from the top of the tank and cutting the top so the tank is ready for welding.

If you wish to repeat this process, the steps are;
Cut off the handle with a hacksaw. Grind smooth.
Draw a circle the OD of the pipe
Make a ring of center punches inside the circle
Drill the ring of punches.
Enlarge the holes
Remove material between the holes
Trim and bevel until the pipe fits.

The bevel and enlarging of the hole to size is done with a ball peen hammer.

@ Brian, this is being designed to have a working pressure of 200 PSI. I will use it to develop a robust bumper for the 3 and 4 inch versions.

auxiliary · Thu Oct 15, 2009 8:15 pm

I can't wait to see this thing in action! I do have some advice though. When I built my 2.5" QDV tennis ball launcher, (4" PVC chamber coaxial never posted because trigger handle broke) I found that materials such as solid plastic had too much inertia and blew the back out of the cannon on the second launch. I instead used 2" PVC pipe and plugged both ends to make a much lighter piston. As for o-rings, 2" PVC Unions (both sch40 and 80) have o-rings that fit perfectly in 2.5" sch40 PVC pipe. With this piston, it sealed well, actuated faster, and didn't give you a massive jolt when fired. Good Luck!

Technician1002 · Thu Oct 15, 2009 11:48 pm

auxiliary wrote:I can't wait to see this thing in action! I do have some advice though. When I built my 2.5" QDV tennis ball launcher, (4" PVC chamber coaxial never posted because trigger handle broke) I found that materials such as solid plastic had too much inertia and blew the back out of the cannon on the second launch. I instead used 2" PVC pipe and plugged both ends to make a much lighter piston. As for o-rings, 2" PVC Unions (both sch40 and 80) have o-rings that fit perfectly in 2.5" sch40 PVC pipe. With this piston, it sealed well, actuated faster, and didn't give you a massive jolt when fired. Good Luck!

My first QDV the apple cannon does have a PVC piston. (See my ABS Test Cannon) I have built several PVC piston cannons and they all fatigue pistons. The piston has a finite service life. This is the primary reason I have moved away from PVC except for barrels. The apple cannon is the only cannon I own that hasn't broken a PVC piston yet.

As far as weight, it has been a non issue with HDPE. The only "Massive jolt" I get is recoil with launching high mass projectiles in the larger diameter barrels. A large Gatoraid about knocks people on their butt.

HDPE has held up well to extensive testing at high pressure and heavy field testing. My 2 inch cannon has a spare piston if I need it, but I haven't needed it. The same is true for the Marshmallow cannon. I use the spare piston as a show and tell item. It is the piston I show the floating o rings on in my using o rings youtube video.

For recoil control of the piston, a substantial bumper is used along with a crushable piston stop that is regularly examined for damage. In the Marshmallow Cannon this is PVC due to the small 1 inch piston. In the T shirt cannon this is ABS. So far I have had no measurable damage to the piston stops in either. The foam pad in the Marshmallow cannon is showing extensive crushing. Part of the new build will be to test a new bumper to handle the higher mass piston on higher pressure.

Technician1002 · Sat Oct 24, 2009 1:43 pm

Bumping to post this weeks update.

I've been sanding like crazy. The way I sanded it is to use self stick sanding pads and stick one edge onto a 2 inch ABS pipe. I stuffed paper towels under the flap to provide pressure. Then it was several sessions of getting a workout. First came off a layer of rust. Then I started to cut through the black pipe finish in the area of the seam. Now I'm starting to wear through the black finish down to steel all the way around and the full length. A couple more days sanding to sand down the seam and remove all the black finish is the goal before cutting ports.

I am taking it in to get it threaded on both ends this after noon, my first major expense. It will cost $7.50 for each end threaded.

I decided to test those camera batteries that went into low batt wink mode on my camera while shooting a golfball target shot. I tested them and the strength of my 2.5 inch valve material. The valve held up with nary a mark. The batteries didn't fare so well. Test conditions are point blank range, 1/2 inch conduit barrel 7 feet long on the Marshmallow cannon at 100 PSI.

Moonbogg · Sat Oct 24, 2009 6:03 pm

Could you sand with the power drill and rod method? I tried sanding like you are to hone the inside of a barrel and I almost died trying until I read someones how-to on "improving the barrel" (forgot their name sadly). Their method actually works very well. I was very pleased. If you haven't read it and want to, i'll find the post for you.

EDIT: I figure you may already be well aware of this, but I thought i'd try to help anyway.

Technician1002 · Sat Oct 24, 2009 6:48 pm

Moonbogg wrote:Could you sand with the power drill and rod method? I tried sanding like you are to hone the inside of a barrel and I almost died trying until I read someones how-to on "improving the barrel" (forgot their name sadly). Their method actually works very well. I was very pleased. If you haven't read it and want to, i'll find the post for you.

EDIT: I figure you may already be well aware of this, but I thought i'd try to help anyway.

You figured right. I moved to a power drill to drive the sanding process. Due to the large amount of scale and black pipe surface, I switched to 80 grit for the bulk sanding. I found a drywall sanding screen works well, but wears out quickly. This is much larger than the sanding job on the 2 inch or the Marshmallow cannon.

I do have an update and some good news. I got the pipe threaded this afternoon. Last week I was quoted $7.50 per end to thread it. I took it in and they charged me only $10 to thread both ends. I also exchanged o rings. Some in the bins were mixed up so I originally got the wrong size. The correct ones fit like a glove. Only a very slight compression is required to fit them in.

Even though the ID of the pipe is a shade larger than 2.5 inch, the 2.5 inch rings fit perfectly.

Next week I should be ready to cut the ports so it is ready to make the piston the following week.

This is going together smoothly.

The pitted areas where the rings will set will be sanded out with a soft backing so they are very rounded to permit the ring to seal. Deep pits will be epoxy filled and sanded smooth.

Running tally of the cost is $11.60 not counting consumables.
Pipe threading $10
2 o rings 0.80

Check out my YouTube SpudGun Channel! · Sat Oct 24, 2009 6:55 pm

Looking good, did you sand the entire length of the pipe?

Technician1002 · Sat Oct 24, 2009 7:05 pm

MrCrowley wrote:Looking good, did you sand the entire length of the pipe?

The entire length is sanded. More attention is given to the area the rings will seat. Due to the design and a planned piston stop to prevent the piston from launching, the piston will have to be serviced out the breech like the marshmallow cannon. Due to that, there can't be any high spots in the pipe. They are all sanded off. This is one of the reasons this valve is taking longer. The pipe is in worse shape to start with. I picked it because the seam is not in a deep valley like some I was considering. It's easier to sand off peaks then it is to fill in a valley. Some pipe has a terrible seam. Either a tall ridge or deep valley. I decided to deal with some rust pitting instead of a bad seam.

tghhs · Sat Oct 24, 2009 9:22 pm

Woah, Epic cannon! man that must have taken ages to sand that barrel. It does look alot better though!

theBOOM · Sat Oct 24, 2009 9:35 pm

It isn't a barrel its basically where the piston is held ... Good job on the build tech looks very clean. and much better than how it looked before you sanded that piece of pipe.... I wonder why the seam on some pipes are so big... in 1/2" galv. pipe its about 1mm tall, might want to look for some seamless steel piping...

Just1ChanceFree · Sun Oct 25, 2009 1:21 am

So this is what you've been working on! looking good man, I'm impressed how well that rust is coming off--hopefully it didn't decrease the structural integrity of the pipe. You might have to consider mounting this (or any larger) monsters just for recoil's sake--good on ya!

Thanks again for helping me out through pms, I'll get back to you with more once I have worked through a few more of those ideas. I'm having (getting) to scale-down the entire project because the QDV simply makes the thing too powerful.

You may have this explained elsewhere, but what do you use to install the piston stop? Drill through and weld something shut to stop it firing?