The snorkel is simply a curved tube that lets you breath while floating face-down on the surface of the water. When diving, it is used to conserve air in your tank while on the surface. They also offer hours of enjoyment for snorkelling in the shallow waters allowing you to keep your head underwater.
This is a one-way valve that allows water to be cleared from the snorkel from the lower end, thus reducing the effort required for clearing.
In certain snorkels, the valve is located directly below the mouthpiece; others incorporate a shotgun design with a valve on a separate branch from the main tube.
Better snorkels have a small chamber around the purge valve to collect water before its purged, stopping water from going into your mouth.
Many modern snorkels incorporate a system that reduces the amount of water entering the open end, for example if a wave washes over your head known as a wave chamber.
Many people recall a ping pong ball on the top of a snorkel to stop any water entering the tube, this system is no longer available.
However newer versions of this are available that have a valve system to stop water flooding in.
A flexi-tube on the snorkel mouthpiece keeps the snorkel out of the way while underwater, and can be bent back round to the most comfortable position when Required.
Better snorkels such as the TUSA Platina Hyperdry snorkel have a corrugated flexi-tube but the inside is smooth so the air flow is not disturbed making each breath much easier.
Internal corrugation causes turbulence that increases breathing resistance and makes it difficult to completely clear out the water (right). Better snorkels are smooth inside which allows the water to flow through better (left).