This is my first instructable so hopefully this goes well. If you have questions please let me know.
I read Kaiven's instructable here:
and I wanted to make one with what I call improvements. I didn't like the tubing at the top and blowgun triggers are kind of expensive. Kaiven has a lot of good information in his post so I won't put in as much detail in this but I will go through how I assembled mine and some of the changes I made.
I am just going to go through making the trigger chamber assembly and leave the rest of the assembly up to you.
Caution: This is not a toy and can be dangerous if used or built improperly. I take no responsibility to any injury or damage to anything. Do your research before attempting to build anything of this nature. It can save your life.
Step 1: Pieces Needed
The pieces I used to make mine are as follows:
2-90 degree elbows
2-end caps that fit in the cross pieces
2-screw in air valves
I laid out my pieces to make sure that the pieces were where and how I wanted them.
The two lower unions are your burst disk holders.
I would not recommend putting any more that 100psi in one of these. I know the rated pressure is higher but when these fail it is catastrophic sometimes.
Step 2: Putting in the Valves
The pictures kind of explain it all.
Drill a hole in the end caps and screw the valves into them.
The way I find the correct drill size is to drill holes into wood first and test fit. I will make sure the threads get a good grip on the wood as I screw it in. Once you find the proper drill size you can drill the end caps and add the valves. If the fittings leak just use some thread tape and putty to seal it.
Step 3: Cutting the PVC
I wanted all my pieces to be butted against each other to make it as compact as possible.
I needed 1.5" long pieces of PVC to accomplish this.
I used .5" PVC for mine. If your pieces are bigger than mine you will need longer pieces. Measure twice and cut once. It saves PVC pipe.
Lay out all of the pieces where they need to go to make sure you have all the pieces you need for assembly.
I left out one piece from my layout because it is the long piece needed for the trigger chamber and I knew I needed to measure it after assembly of the other pieces.
Step 4: Assembly
I assembled all the pieces slowly. I used PVC primer and cement to put it all together.
Make sure the pieces are lined up as you go. A misaligned piece can make it so it won't screw together properly or at all.
The missing piece from the last step I measure and cut after completely assembling all the other pieces. And it fits nicely where it needs to go.
This is the finished assembly of the trigger chamber.
Step 5: Air Chamber
Add an air chamber to hold the pressure behind the disks.
You can add the pressure gauge behind the rear burst disk using the same method to install the air valves. You can see the pressure gauge in the first picture posted.
Step 6: Loading Burst Disks
Load the burst disks where they need to go.
I cut the disks from foil which has about a 50psi failure at the size opening I have.
Once disks are installed it can be filled with air and fired
Step 7: Filling With Air
Check out this page:
it explains how a triggered system works.
To fill my design you fill from the rear valve using these steps:
1. open ball valve if not open
2. fill with 25-40 psi ( almost any pressure under failure rating of burst disk. Should be about half.)
3. close ball valve ( this traps the pressure in the trigger chamber)
4. fill air chamber past burst rating of disks ( this works because the pressure in the trigger chamber pushes against the pressure in the air chamber causing the disk between not to fail.)
5. disconnect air fill line and prepare for firing
6. use forward valve to dump pressure in trigger chamber ( this causes the air chamber pressure to break the rear disk and pushes through the forward disk as well.