If you have been researching masks for snorkeling you may have come upon some whose descriptions include something called a "purge valve". This is a mechanism that is pretty simplistic in design which allows water to be expelled from the mask. It is usually found in the area of the skirt area that covers the nose and usually consists of a hard round pastic piece that has holes in it. A soft silicone disk with a stem is located on the outside of this disk which creates a one way seal to keep water from entering. If the user exhales into the mask it creates a positive pressure and the excess air escapes through the purge valve by pushing the silicone disc away from the round plastic support. If water is in the way, it will push that water out as well. While this mechanism sounds like a new feature, you might be surprised to find out that the first mask that included a purge valve was the Equi-Purge from U.S. Divers in 1962. These early masks were considerably larger (volume wise) than many of the masks that you find today.
Your research into masks has probably ingrained the idea that fit is the most important feature of during the selection process. While this is true, even the best fitting style may at one time or another end up with a little water getting into it.This could be caused by improper strap placement, having the adjustment strap too tight or too loose, hair breaking the seal of the skirt or it could even even happen from a simple change in facial expression such as smiling. Those people with mustaches often find this facial hair to be main culprit for water entering. Whatever the reason, the result is the same, there is water in your mask and you don’t want it to be there.
Taking it off to dump the water is the most common solution, though it isn’t always the best way. Ideally, for a mask without a purge, you would place the palm of one hand on the upper frame of the faceplate exerting some pressure and exhale through your nose while tilting your head back. This method does require practice to execute correctly because you have perform multiple movements while exhaling just the right amount of air. Masks with a purge valve are cleared in a slightly different manner. Holding it firmly in place, exhale through the nose with the head tilted downward. In both instances of clearing, the air from your exhalation rises to the top and since you are not allowing that air to escape, it has to push the water out of its way to find the easiest area to exit which is either along the bottom seal or through the purge valve.
With regard to the nose pocket area of the mask, some older style purge valves did have a tendancy to occupy more of this space than the newer styles. This did tend to cause a bit of discomfort for people whose noses needed to occupy the same space. It is good to see that manufacturers are addressing this issue.
A mask with a purge valve does require a bit more care than one without. It is important to keep it clean and free of sand and grit, which can interfere with its proper function. Also, as disgusting as it may be, we often end up having more than just air coming out of our noses when we exhale. Rather than dwell on that particular aspect, let’s just say that rinsing with using a soft bristled toothbrush will help to keep purge valves functioning well for years to come.