SpecialTee Valve pics burst disk gun.

[clide]

Welp, I just finished my SpecialTee Valve. It works OK, but I have some questions I hope you all can help me with. First I'll show you the valve
<a href="http://members.cox.net/clide/specialtee/side.jpg"><img src="http://members.cox.net/clide/specialtee/side.jpg" height=208 width=458>

http://members.cox.net/clide/specialtee/side2.jpg
http://members.cox.net/clide/specialtee/takenapart.jpg
http://members.cox.net/clide/specialtee/piston.jpg
http://members.cox.net/clide/specialtee/inside.jpg
http://members.cox.net/clide/specialtee/inside2.jpg

Basically, it uses a piston with a rod on it to burst the burst disk when I want it too, rather than when the pressure wants to.

But here is my problem.
http://members.cox.net/clide/specialtee ... 0disks.jpg
As you can see in that picture a large majority of the burst disks do not burst completely, limiting the flow.
The top section is materials that didn't work to well. They include aluminum and windshield wiper bottle (I didn't test too many different materials)
The bottom right section is all the partially broken disks. It frequently left about a 1/3 of the disk remaining. Some were sliced with razors in various ways and some not, and they were fired at various pressures.
The bottom left are the ones that worked, unfortunatly only one of those worked like it was supposed to, the rest burst from pressure. The one that did work was sliced slightly with a razor and fired at 100 psi.

Here is my question for you. Any ideas on how to get the full disk to burst out of the union when struck by the rod?

Edit: typo

[BewareOfDog]

On the end of your rod, instead of the nut, install a cutter from one of those mini- vegetable choppers.

Or, a piece of pipe the same diameter as the pipe that the piston rides in, that is filed to a sharp edge, like a cookie cutter?

[akb]

Very innovative design, clide!

Brainstorming on.

Arrange the 'rod' to punch a bunch of small holes or slots around the periphery of the disc - creating a dotted circle.

Use layers of weaker material, something that 'tears' well, like aluminum foil or ...

Use razor blades on the tip of the rod to cut a big X in the disc.

Hit the disc at the edge all around - with a metal tube that is sharpened, or has pointy teeth - to 'cut' a large disc' at once.

-- akb

[clide]

Hmm good ideas, kinda along the lines of what I was thinking.

Any idea on how to attatch these things? I don't really have access to welding equipment. Also I may have trouble with the punch it out around the outside method because my piston isn't too strait**, so it would be hard to position it right.

**acctually its the back tube thats not strait, the slightest bit of offset makes a pretty large difference in the front

[akb]

The 'cutting tube' can ride in the forward tube. 'Tow' it with a couple of strong wires from the tip of the bolt back to the edges of the tube at a 45 degree angle. Can be quite flexible as long as it 'tows' the tube. The bolt can hit the disc in the middle a bit after the leading edge of the tube.

I think triangular sharp 'teeth' on the edge of the tube are best.

-- akb

[clide]

ah, great idea. 1.5" fits perfectly through he union hole and will fit through the male adaptor with a little grinding. So I will use some sdr21 and try to rig that up sometime, hopefully tomorrow if I can.

[clide]

Success!!! I think...

First I tried the tow method as akb suggested, but I didn't have any thin cable that was strong enough, so it kept breaking.
Next I tried to drill 4 holes in the front and put fishing line through those so it grabbed the bolt and wrapped around the bolt several times. That came untied and wouldn't work too well.
Then I ended up with what I have now. I ran a screw through the front and grinded the ends off, then put a nut with a V grinded in it on the end of the rod to ensure it didn't slip off to the side. It was still having problems because I had too many teeth on the new part. It looked really cool and had teeth all the way around, but I had to grind all but 6 of them off. It works now and punches a perfect hole. Fortunately it has enough friction to not shoot out when I fire the gun.

Unfortunately, my pressure gauge seems to have broken so I didn't get to see if it would work at lower pressures because I had no idea what pressure I was at.

Pics:
<img src="http://members.cox.net/clide/specialtee/bursttip.jpg">
<img src="http://members.cox.net/clide/specialtee/bursttip2.jpg">

[PCGUY]

Clide, would you mind writeing a little something to go with the pictures so I could add it to my site. All I need is comments for the pics, and a brief description on how it works.

Nice looking valve

[clide]

Here ya go PCGUY

The goal of the SpecialTee Valve is to be able to control burst disks, so I can make them burst when I want, rather than when the pressure wants.

http://members.cox.net/clide/specialtee/specialtee.jpg
The rear piston area is sealed off from the pressurized chamber. A rod from the piston is ran through the blue sealing wall and is sealed with an o-ring as it runs through it. Pressurized air from the chamber is ran through a a valve to behind the piston. When I open the valve it moves the piston forward from the pressure behind it. The rod is then connected to a tip that is pushed into the outside edges of the burst disk. The burst disk, already being under heavy stress from the pressure is then burst from the impact of the tip.

http://members.cox.net/clide/specialtee/side.jpg
This is my finished version. As you can see there is a hose running from the front pressurized area to a blowgun which is connected to the rear of the piston area.

http://members.cox.net/clide/specialtee/side2.jpg
The pressure guage and fill valve, you can also see the screws used to hold in the piston tube

http://members.cox.net/clide/specialtee/takenapart.jpg
Opened for piston removal

http://members.cox.net/clide/specialtee/piston.jpg
A shot of the piston. The rear part fits in the piston tube and the front part fits in the 1" hole running through the sealing wall.

http://members.cox.net/clide/specialtee/inside.jpg
Looking down the front, you can see the sealing wall in the back made from 2 chopped bushings and 1" pipe.

http://members.cox.net/clide/specialtee/inside2.jpg
Another view from the front with the piston in. You can get an even better view of the sealing wall. (the piston tip is not in)

http://members.cox.net/clide/specialtee/bursttip.jpg
http://members.cox.net/clide/specialtee/bursttip2.jpg
A couple shots of the piston tip. Without the tip, the burst disks I was using would not completely break. There are six points around the tip to burst the disk, and a screw with the ends cut off running through it for the piston to push it. (This tip is broken now. It flew out of the gun durring a test shot. I didn't see it happen, I just found it later. I am working on a better tip now)

[PCGUY]

Thanks

Now I have all kinds of things to add.