Does anyone know how to hook up an air tight system to the soda cap so you can suck out the air to a vacuum and then fill it with gas at some where 80 PSI with a Hand Pump

No, but use protection against the soda bottle exploding...

Soda bottles explode at 120 PSI.

there are special caps you can buy that stop soda from going flat by pumping in air (a little hand bulb) they don`t cost much either.

you could modify one of those much easier than a regular cap

Awsome, I will try to find one.

this: http://www.linktotheweb.com/04kitchen/fizz_keeper.htm

is what they look like.

I saw one for wine at the dollar store I will check for soda bottles pump things next time I go.

just because you seen a reference to soda bottles exploding at 120 PSI is no reason not to have some form of shield for 80 PSI

just because you seen a reference to soda bottles exploding at 120 PSI is no reason not to have some form of shield for 80 PSI

 

Especially considering the weakening of the system when you flatten it by trying to draw a vacuum first. Embrace the concept of a safety margin.

I going to use these:

http://www.stevespanglerscience.com/product/1367

well that`s fine, but you mentioned a vaccum, how do you intend to evacuate the tube?

they don`t look like they would squish down very easily, and heating then cooling won`t make too terribly great a vacuum either.

i once built an "anti simian cannon" to demonstrate the monkey and hunter principle (my physics teacher asked for a replica)

anyway, it used soda bottles, the 600ml ones can stand around 250psi, (dont quote me)

i used 25mm retic pipe with a lid titan bonded:

http://www.bostik.com.au/pdf/datasheet/bostik_titan_bond.pdf#search=%22titan%20bond%20plus%22

it in place. the lids you get with the bottle should fit rather snugly in the pipe.

i drilled out the centre of the lid and glued it in the pipe.

 

this config was tested several times to 90psi with a 2L bottle without fail.

(the gun was built modular so it's grown to ridiculous proportions)

 

i'll put up a pic of the lid in the fitting. the type of lid is also important, i found ones with a good seal design and complete threads on a water bottle, they also fit perfectly in 25mm pipe.

 

the inlet valve was cut from a bike tube and glued into a pvc end cap.

again, i'll put some pics up.

[ATTACH]1397[/ATTACH]

sorry about the image quality, but you get the idea, the cap is inside a pipe in a fitting.

the other, larger object is the assembled inlet valve piece, the valve itself is shown as well. (note the circle of rubber still attached, this allows it to hold pressure without blowing off)

everything is set up with screw connections for easy modification, this is the most versatile thing i've ever made, i can get gasses to super saturate water, turn it into a water rocket, water gun, gas gun for cleaning dust, and of course demonstrate balistics.

a word of caution... this sort of thing is VERY dangerous, im assuming you're using a 2L bottle, 2L @ 80 psi gives an explosive decompression, venting this amount of gas quickly applies huge forces. shrapnel from shattered pvc can be lethal, you should wrap the whole thing in a teatowel (or other strong fabric) as well as stand back. 80psi in a bottle will allow it to resonate when it's struck.