In a conventional snorkel, the opening at the top end thereof is only about 10-15 cm above the water level when the diver is floating. The tail end communicates with the diver's mouth, so a trifling carelessness (such as the snorkel is inclined) or a wave on the water surface may cause water to flow into the snorkel mouth and lead to the danger of swallowing water or choking the bronchia with water.
After purging water from a conventional snorkel, there is usually some residual water remaining in the lower portion of housing. Oftentimes the amount of this residual water is sufficiently little so that the diver may breathe past without significant “gurgling” noises, but is still enough to effectively reduce the breathing passage size such that breathing resistance is increased. Although the snorkel may equip the water valve, water is still hard to be repelled if water stays in some particular positions. Therefore divers must float to the water surface, take off the snorkel, and drain the water out, which is very inconvenient. However, decreasing the amount of water entering the snorkel becomes an important subject to the snorkel industry.