A percolator refers to any type of water pipe which helps in cooling down cannabis before it is inhaled. This is achieved by pressuring the smoke to filter right through the water. While you cannot see this filtering process happening inside, you can hear that bubbling sound inside the bong. This is the percolator doing its task.
If you are used to a bong but not use a percolator, you will eventually realize the difference that it offers. Why? The overall smoking experience is much smoother and easier to inhale when using a percolator. The secret to having a great percolator bong is the involvement of diffusion, which is characterized by the movement of a substance from a highly concentrated area to a low concentrated one. This happens in liquids and gases because the particles randomly move from a place to another.
The filtering process offered by a percolator bong helps in cooling the smoke by getting it in contact with water. The percolator allows for a large surface smoke area to reach the water, thus helping it to cool even more. With the bubbles becoming even smaller, the result is a cool and smooth bong hit!