Airlocks are structures effective at preventing water (and mobs) from spreading into buildings. The airlocks shown here will close in the event of flooding, but will not reopen until the player breaks them. The designs shown here are not true airlocks, but are simply watertight compartments to close in the event of flooding. Using a door is more like a true airlock.
- Torches can support other blocks, and they turn back into an item if the block it is attached to is removed or if it is exposed to water.
- Sand will always attempt to fall and can be supported by a torch.
- Water flows outwards, but will dry up if not connected to a block of still water.
When a torch with sand on top of it touches water, the sand drops and stops water flow in that direction. If torches are attached to any of the blocks above, then that torch will break as well. This will continue to the very last torch.
 Design 1
An airlock requires only two components, a block affected by gravity (such as sand) and torches (regular or Redstone). When placing an airlock, be sure to think about choosing narrow passageways and choke points, so that less time is spent on the project. For a building with multiple entrances, multiple airlocks may be needed to achieve optimal dryness. Airlocks are usually 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 to 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. A torch is placed on either wall at a level where water can contact it and there is enough space above to provide the required amount of sand to seal the chamber. Sand is now placed above the torch until the sand reaches the ceiling, or until it reaches the desired level.
(A 1 block wide hallway is complete at this step)
A passageway more than 1 block wide must be extended from wall to wall in a particular fashion. A torch is placed on the block of sand above the previous torch, and sand is placed above that. This process is repeated until the hall is waterproofed.
 Design 2
Sugar Cane can be used as a type of airlock, though this presents the difficulty of growing it inside.
 Design 3
Since the introduction of Pistons, they can be used to make much more compact airlocks using the same basic techniques. Piston-based airlocks are not restricted to using sand or gravel, but they may require redstone circuitry which tends to make them costlier and more complex than torch/sand or torch/gravel airlocks. A simple way to build one would be to make a piston system that is retracted when the current is stopped and then placing redstone across the passage.
 Other Uses
The use of Airlocks in stopping water flow can also be applied to the concept of controlled flooding, allowing one to flood an area until a certain water level or redirect it when those levels are reached.
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.
- Torches will also support gravel.
- Regular torches can also be substituted with Redstone Torches, but this is usually pointless, due to the increased expense.
 Video Guide
|How to build an airlock Video (view on YouTube)|