Tutorials/Airlock

Airlocks are player built structures designed for the Indev Version of Minecraft. They can be used to effectively limit water from spreading into your base if your base is in danger of frequently flooding. These airlocks are one-way, meaning they will close in the event of flooding but will not reopen unless the player breaks them.

Airlocks can still be used in Beta, although reeds and doors can be used instead of sand and torches.

How They Work
Airlocks rely on the current interesting properties of torches, allowing the torches to support blocks of Sand above themselves until they are removed. In this case, when water comes into contact with the torch, the torch vanishes. This releases a large pile of sand, which in turn removes the support for the second torch. This cycle can continue for as many torches as you want and therefore works very well in most hallway sizes. This is also one of the very few reactions that can occur without a player's direct assistance.

Construction
An airlock requires only two components, a block affected by gravity (such as sand) and torches.

When placing an airlock, be sure to think about choosing narrow passageways and choke points, so less time is spent on the project. If you have multiple entrances, then multiple airlocks may be needed to achieve optimal dryness.

The airlock is built directly across the hallway. Most sand-based airlocks are only 1 block thick, due to the fact that only 1 layer of sand is needed to stop the water.

Determining the materials needed is simple enough. The number of torches is equal to the width of the corridor, and sand is equal to the width of the corridor times the height of the corridor. Optionally, a shovel and a pickaxe can be taken along, to speed up digging and waste less time on mistakes.

For the first step, the hallway must have a ceiling height equal to the highest water level possible plus 1, to compensate for the torch. Also, each new column must be 1 block higher, as the torch is 1 block higher each time.

You would take the first torch and place it on either wall at the roof's height. This is the torch that will be triggered by the water and therefore MUST be at a level at which water will contact it.

Next, place sand blocks up to the ceiling, above the torch. The blocks of sand will be supported by the torch and will fall down to block the hallway the instant that water contacts the torch, which turns your torch into a collectible item. (This is all you need if your hallway is only 1 block wide)

If your hallway is more than 1 block wide, additional columns must be added. This can be done in multiple ways, but the most effective is to have the first torch directly trigger the second column of sand to fall.

This is accomplished by directly placing a torch on one of the segments of sand that will fall. When the sand drops the torch no longer is attached to anything, and automatically turns into an item, release the successive column of sand. If the hallway is three blocks wide, it would look like this:

=Other Uses= That is to say, they are an effective system for making Sand-Related things happen when water is introduced to an area. Making them one of the first completely environmentally reactive trap in Minecraft.

This concept could easily be adapted to other uses as well. Such as limiting the amount of water flow automatically by shutting off the water source when the water height reaches a torch, or changing the flow of water when the water reaches a certain area, thus "controlled area filling".

Example of Player triggered trap using the torch/sand concept The airlock works essentially the same, but faster and directly controlled by water flow, and not player interaction (Making it a completely standalone mechanism), Although this video proves that the method can be used to effectively trigger multiple walls and seal off multiple areas.

The torch system could also trigger sand falling into a room, where a hole in the ceiling then opens up and lava then pours in to cancel out the water. As long as it involves the movement of sand and water, it's quite an effective trigger system.

Uses in Creative Mode
By using flowers/mushrooms you may be able to build a less effective version of this airlock, since mushrooms/flowers are removed when in contact with a water/lava square. However the efficiency of simply using Trees to block water/lava makes sand based airlocks much less worthwhile.

Trivia

 * Torches will also work with gravel, but the gravel must be placed, not dropped, on the torches, as it breaks without producing any flint.
 * Regular torches can also be substituted with Redstone Torches, but this is usually pointless, due to the increased expense.
 * In Beta, Sugar Cane can be used as a type of airlock, though this presents the difficulty of growing it inside.

Video Guide

 * How to build an airlock