When homebrewers are looking at starting there fermenting they need to consider an essential piece of equipment, the airlock. There are two different styles of airlocks. I get asked a lot, “Which one is better?”. It really depends on what you are looking at doing.
The S-Shape Airlock
This air lock is meant to show pressure. Most of the time it is used for secondary fermentation where the pressure coming out of the secondary fermentation is slower (or not as strong) then in primary. A great way to use these is with wine. The way to use it with wine is, after you add your stablizer to kill the yeast you will see the water start to equal out making it clear when no more CO2 being released, meaning that the yeast has been killed.
Normally I do not recommend these airlocks for primary fermentation (or at least with beer) for a few reasons. One reason is that they are hard to clean out in my opinion. If you have a vigorous fermentation and beer or wine get into the acutual airlock, I just consider it ruined because they are such a pain to clean out. I mean it’s not a lot of money to replace them ($1.19) but it’s the whole fact that you have to drive out and pick it up or order it online, which with shipping is a bit more. So in my opinion, these serve best for secondary.
3-Piece Air lock
This is the airlock that many homebrewers end up using. I prefer this model for primary fermentation for a few reasons. I also use this airlock for both primary and secondary fermentation.
One reason I like this airlock is that is that it holds a lot of water. If you have a vigorous fermentation it allows your beer to spit out a lot of water before you have to refill it. Having this feature is nice because you don’t have to monitor your airlock nearly as much. Because of that, I also use it for the secondary because I can walk away from the fermenter for weeks and not worry about water evaporating and leaving the airlock dry, ruining the beer or wine.
Another reason why this airlock is preferred for primary fermenation is the easy cleaning that comes with it. The name is self explanatory. You can take apart the airlock into three different pieces. If you end up having a fermentation that is vigorous, and beer spills into the airlock, you can take it apart rinse it out and it’s cleaned. Because of that feature I have found that I like this airlock more then the S-shape, but that’s just my preference.
At the end of the day, I’m not really a stickler for either airlock. Truthfully I end up using what ever one I can find first. The thing to consider though is that they both do serve the purpose of protecting the beer or wine. With that said, I hope that this post brings a little clarity that is asked, “Which airlock is better?” the answer is neither, it’s what do you want to do with it.
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Jay's Brewing Blog 
November 8, 2011
2011, Equipment Info, General posting