'Handy' airlock no vent holes??

@Chippy_Tea
I saw the photo of your blow-off apparatus. For my own information, shouldn't the blow-off container be lower than the liquid in the FV? Meaning, don't you risk a reverse-siphon since the liquid in the tube could create a siphon effect in the wrong direction once there's no CO2 pressure coming from the FV?
I usually see the blow-off tubes where there is an airtight connection at the FV and then the tube travels down to a lower position and rests in a container of vodka.

I swap to a standard airlock once fermentation has died down to a level where suck-back could be an issue.

davidfromUS said:

Since you push CO2 out when checking, when the lid returns to its original shape, won't it be air that is pulled in to replace the CO2 just pressed out?

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Hi David, no, if you think about it you are pushing CO2 out but nothing is coming back in that's why we fit them, imagine the bigger ones in a U shape you push the CO2 out around the U bend but you get no water or whatever you have put in back into the FV. Hope this answers your question?

Banbeer said:

Hi David, no, if you think about it you are pushing CO2 out but nothing is coming back in that's why we fit them, imagine the bigger ones in a U shape you push the CO2 out around the U bend but you get no water or whatever you have put in back into the FV. Hope this answers your question?

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Just to make sure: we're talking about plastic FVs that are properly sealed and the only entry point is the airlock.
First, I might not understand that two-piece airlock in the photo and being described, so bear with me. The way I understand it, during fermentation, the top piece rises from CO2 if just set on top or if it is snapped in place, the CO2 seeps out at the top.
I guess I'm stuck on if you press the lid and it goes down, bubbles come out the airlock (three-piece with the floating bell in my case). When you let go, the lid goes back to its original position and pulls gas (air) down into the bucket.
For example, early on in brewing, I carried my plastic fermenter upstairs by the steel handle. This had the effect of deforming the bucket, making it slightly smaller and pushing CO2 out the airlock. When I set the bucket down and it went back to it's original shape, it pulled all of my Starsan into the beer (was upset but turned out not a big deal).
I'm writing a lot here to give you an idea of what's going on in my mind with the purpose of figuring this out.
I would think the fermenter would be akin to a turkey baster with CO2 in the bulb. If I squeeze it, the C02 exits and then to regain its shape, air enters in.
I'm happy to be wrong here; this is just my understanding of it.
*If anyone sees my error and can explain it, by all means, chime in.

I'm not sure what pressure you think I'm talking about but I was working along the lines of slightly pressing the lid to see if the liquid raises so you know that the airlock is working, all my 2 piece airlocks that I have the lid stays in position i.e doesn't move up when the CO2 emits. I've done exactly the same whilst carrying the FV from my kitchen to the beer fridge so now I keep it off until it's in the fridge.

davidfromUS said:

First, I might not understand that two-piece airlock in the photo and being described, so bear with me. The way I understand it, during fermentation, the top piece rises from CO2 if just set on top or if it is snapped in place, the CO2 seeps out at the top.
I guess I'm stuck on if you press the lid and it goes down, bubbles come out the airlock (three-piece with the floating bell in my case). When you let go, the lid goes back to its original position and pulls gas (air) down into the bucket.

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In the video (at 44 seconds) you can see the first bubble push through the airlock.



The CO2 travels up the smallest middle tube from the FV or DJ (blue arrow) then fills the middle-size tube (Red arrow) if snapped on it eventually releases a bubble as the pressure continues to build and if not snapped down the inner tube (Red arrow) lifts slightly allowing the bubble of CO2 to escape the same way as when its snapped shut but a little sooner.
I have a few of these and have found some will snap shut and others don't after a while the ones that do wear and then don't snap shut.
The guy in the video has more fluid in the airlock than is necessary i use just enough to cover the end of the inner tube and that stops the inner tube lifting too much.

Chippy_Tea said:

In the video (at 54 seconds) you can see the first bubble push through the airlock, basically the CO2 goes down the smaller inner tube until its full then if snapped on iteventially releases a bubble and if not snapped down the inner tube lifts slightly alowing the bubble of CO2 to escape the same way as above but a little sooner.

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Thanks. I get the airlock bit. What I didn't get was my discussion with Banbeer about what happens after you press a fermenter lid.

Chippy_Tea said:

You cannot make it 100% airtight or the CO2 would not be able to escape, as long as there is enough of a gap to allow CO2 out it'll be fine i don't mean leave a gaping holes all you need is a very small gap.

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That's why I'm gonna poke a couple of holes in it when I get a chance. Dont need a glass bottle going bang in my shiny new fermenting fridge! !

davidfromUS said:

That is an interesting two-piece airlock. First time I've seen one. If the lid is snapped tight (not left loose as some have mentioned), the CO2 will still escape by seeping through said lid?
The three-piece which does have holes in the lid and a floating "bell" seems a little easier to work with.

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That's where I was getting confused. Thought it should have holes but only the 3 piece ones seem to. And the consensus is that 2 piece ones should clip together and still vent. Mine must have been dodgy. Gonna modify it when this one gets bottled up

Try holding the two pieces together and blowing through the airlock I can guarantee it is not airtight, if I am wrong you don't need to modify it just leave the inner piece resting on top of the outer (don't clip it down) there is no danger of dottle dombs either way.