Editing Snorkeling (section)

== Operation ==
The simplest type of snorkel is a plain tube that is allowed to flood when [[underwater]]. The snorkeler expels water from the snorkel either with a sharp exhalation on return to the surface (''blast clearing'') or by tilting the head back shortly before reaching the surface and exhaling until reaching or breaking the surface (''displacement method'') and facing forward or down again before inhaling the next breath. The displacement method expels water by filling the snorkel with air; it is a technique that takes practice but clears the snorkel with less effort, but only works when surfacing. Clearing splash water while at the surface requires blast clearing.<ref>{{cite web|title=Unit 3- Diving Skills|url=https://www.diveunderwaterworld.com/s/Chapter-3-Diving-Skills.pdf|website=Underwater World|access-date=2022-07-18|url-status=dead|archive-url=https://web.archive.org/web/20190301074655/https://static1.squarespace.com/static/54342f54e4b0e4aae11b49a5/t/5862ea56be6594dfc3b92833/1482877538853/Chapter+3+Diving+Skills.pdf|archive-date=2019-03-01}}</ref>

Experienced users tend to develop a surface breathing style which minimizes work of breathing, carbon dioxide buildup and risk of water inspiration, while optimizing water removal. This involves a sharp puff in the early stage of exhalation, which is effective for clearing the tube of remaining water, and a fairly large but comfortable exhaled volume, mostly fairly slowly for low work of breathing, followed by an immediate slow inhalation, which reduces entrapment of any residual water, to a comfortable but relatively large inhaled volume, repeated without delay. Elastic recoil is used to assist with the initial puff, which can be made sharper by controlling the start of exhalation with the tongue. This technique is most applicable to relaxed cruising on the surface. Racing finswimmers may use a different technique as they need a far greater level of ventilation when working hard. 

Some snorkels have a [[sump]] at the lowest point to allow a small volume of water to remain in the snorkel without being inhaled when the snorkeler breathes. Some also have a [[non-return valve]] in the sump, to drain water in the tube when the diver exhales. The water is pushed out through the valve when the tube is blocked by water and the exhalation pressure exceeds the water pressure on the outside of the valve. This is almost exactly the mechanism of blast clearing which does not require the valve, but the pressure required is marginally less, and effective blast clearing requires a higher flow rate. The full face mask has a double airflow valve which allows breathing through the nose in addition to the mouth.<ref>{{cite web|title=Full Face Snorkel Mask Reviews – Tribord EasyBreathe Alternatives and Best Prices|url=https://snorkelstore.net/full-face-snorkel-mask-review-lower-price-lower-quality/|website=The Snorkel Store|date=August 2015 |access-date=2022-07-18}}</ref> A few models of snorkel have float-operated valves attached to the top end of the tube to keep water out when a wave passes, but these cause problems when diving as the snorkel must then be equalized during descent, using part of the diver's inhaled air supply. Some recent designs have a splash deflector on the top end that reduces entry of any water that splashes over the top end of the tube, thereby keeping it relatively free from water.<ref>{{cite web|title=Splash-guard for snorkel tubes|url=https://patentimages.storage.googleapis.com/01/fe/9a/6038e50865f3f1/US5404872.pdf|date=April 11, 1995|website=US patent 5,404,872|access-date=2022-07-18}}</ref>

Finswimmers do not normally use snorkels with a sump valve, as they learn to blast clear the tube on most if not all exhalations, which keeps the water content in the tube to a minimum as the tube can be shaped for lower work of breathing, and elimination of water traps, allowing greater speed and lowering the stress of eventual swallowing of small quantities of water, which would impede their competition performance.<ref>{{cite web|title=Finswimming Snorkels|url=https://monofin.co.uk/blog-snorkels.html|website=Monofin|access-date=2022-07-18}}</ref>

A common problem with all mechanical clearing mechanisms is their tendency to fail if infrequently used, or if stored for long periods, or through environmental fouling, or owing to lack of maintenance. Many also either slightly increase the flow resistance of the snorkel, or provide a small water trap, which retains a little water in the tube after clearing.<ref>{{Cite web|title=Snorkel Care|url=https://www.scubadoctor.com.au/care-snorkel.htm|access-date=2021-03-15|website=The Scuba Doctor|language=en-au}}</ref>

Modern designs use [[silicone rubber]] in the mouthpiece and one-way clearing and float valves due to its resistance to degradation and its long service life. [[Natural rubber]] was formerly used, but slowly oxidizes and breaks down due to ultraviolet light exposure from the sun. It eventually loses its flexibility, becomes brittle and cracks, which can cause clearing valves to stick in the open or closed position, and float valves to leak due to a failure of the valve seat to seal. In even older designs, some snorkels were made with small "[[ping pong]]" balls in a [[Cage (enclosure)|cage]] mounted to the open end of the tube to prevent water ingress. These are no longer sold or recommended because they are unreliable and considered hazardous. Similarly, [[diving mask]]s with a built-in snorkel are considered unsafe by scuba diving organizations such as PADI, BSAC because they can engender a false sense of security and can be difficult to clear if flooded.

A snorkel may be either separate or integrated into a swim or dive [[diving mask|mask]]. Usage of the term "snorkel" in this section excludes devices integrated with, and opening into, swimmers' or divers' masks. A separate snorkel typically comprises a tube for breathing and a means of attaching the tube to the head of the wearer. The tube has an opening at the top and a mouthpiece at the bottom. Some tubes are topped with a valve to prevent water from entering the tube when it is [[Underwater|submerged]].

The total length, inner diameter and/or inner volume of a snorkel tube are matters of utmost importance because they affect the user's ability to breathe normally while swimming or floating head downwards on the surface of the water. These dimensions also have implications for the user's ability to blow residual water out of the tube when surfacing. An overlong snorkel tube may cause breathing resistance, while an overwide tube may prove hard to clear of water. A high-volume tube is liable to encourage a build-up of stale air, including exhaled carbon dioxide, because it constitutes respiratory [[Deadspace (in breathing apparatus)|dead space]].