No Siphon Tube. It is stored in the cylinder as a liquified compressed gas, ready for discharge at any time. It is self expelling (The CO2 gas itself is the pressure source for the extinguisher.) Also never put your bare hand in front of the horn at the end of the hose while the extinguisher is discharging unless you want frost bite. We had a genius in our dept a few months ago who thought he would test that theory lol.
co2 fire extinguishers do have a siphon tube . they were right about the fact it works on presure to push out the liquid which when it comes out of the hose or horn then turns to a gas. the co2 extrg. when released from the container expandes 500 its time size. the temperature of the co2 or carbon dioxide when it comes out is 109 degrees below 0 . the way to find out about the siphon tube is simple first hold in the normal position and start to set it off you will take note how it operates properly . now invert the extinguisher and set off you will note it only pushes out gas if you held it in that position long enough you will be able to see the extrg. turn frosty the reason is the gas has been bleed off and liquid has turned to a solid if you let it stand for a while it will reconvert to a liquid and can be set off in the normal operation . a co2 tank for a tap system has no siphon tube because if it had a tube it would feed liquid co2 into the regulator and possibly ruin the regulator plus the regulator only requires about 10 psi. to feed into the keg . i own my own fire extrg business for 30 years i worked for a co.for 7 years and was service manager and i also ran the fire extrg shop in the military . you can also see a picture of this in the nfpa 10 manual . i don't know were the other guys received ther info but they are wrong . take it from a guy with 39 years experience .
In defense to my answer, With all the in house and state NFPA training I have received I had only known of the information I listed in my first post relating to CO2 extinguishers. I am certainly aware that not every firefighter knows everything there is to know about everything in the fire service. No matter how many years you have put in due to the dynamics of the job. Here in CT we only re-fill and pressurize our Stored Pressure Water Extinguishers (Water Cans) all other extinguishers (Dry Chem's and CO2's) are sent out to be serviced by a seperate contractor that our department employs. Thank you to Blaine for providing the information on siphon tubes' in CO2's it is a new piece of information I can now add to my knowledge. Stay safe everyone!