Counter pressure bottle filler

[Izzie1701]

I am looking to make a multi bottle filler. I have watched several videos and done quite a few searches but cant wrap my head around one thing. All use a pressure relief valve to regulate the bottle pressure. With the DIY beer gun on here the bottle pressure is purged whenever it equals the keg pressure and stops flow by slightly breaking the seal of the bung which makes sense as all the gas is at the top. Now my confusion comes from the fillers that dont require the bung to have its seal broken and have the pressure relief valve to purge this pressure. How is the CO2 venting out of the pressure relief valve but the dip stick in the bottle is going to the bottom of the bottle. Should this not allow beer to escape as the pressure would push the beer back up the dip stick and out the pressure relief valve? From what I see on youtube its just a barbed connection with a silicone line going through the bung not sleeved air port or anything like that. I cant seem to wrap my head around this so was hoping someone would have an idea.

 

[crane]

These have 2 different tubes one inside the other. An inner tube that goes all the way to the bottom of the bottle for incoming beer/CO2. The outer tube stops at the bung and allows gas at the top of the bottle to be pushed out the PRV.

 

[microbusbrewery]

Exactly as crane described. Take a look at the picture on morebeer's site. You can see how the outer tube stops just below the bung. The inner tube, the one that delivers the beer, passes through the outer tube and reaches near the bottom of the bottle.

https://www.morebeer.com/products/counter-pressure-bottle-filler.html

 

[Izzie1701]

Exactly as crane described. Take a look at the picture on morebeer's site. You can see how the outer tube stops just below the bung. The inner tube, the one that delivers the beer, passes through the outer tube and reaches near the bottom of the bottle.

https://www.morebeer.com/products/counter-pressure-bottle-filler.html

Thats kinda what i had thought but the one youtube video has a guy using a silicone tube to the bottom of the line. maybe its just in the bung and you cannot see it from the video but it confused the hell out of me. Everything i stayed awake for in physics class didnt make sense with that video.