What is an O-Ring? An o-ring is really nothing more than a thick rubber band! They are almost always round, or O-shaped, but can be rectangular, oval, trapezoidal, or any shape required to establish a watertight seal. In cross section, they are almost always perfectly circular, although some + shaped o-rings are being used today as well. O-Rings are always made of an elastomeric material, which is a fancy way of saying they can stretch and deform. They can be made of natural rubber, latex, silicone, viton, or many other stretchy materials. This is an important feature of o-rings as it provides the means by which a watertight seal is formed. How do O-Rings work? O-Rings are installed where two mating surfaces come together and a watertight seal is required. Looking at two such mating surfaces (like a housing) in a cross-sectional view, with water on the outside and your electronics on the inside. When the housing is submerged, pressure is exerted on all sides of the o-ring exposed to the water. The o-ring is then squeezed toward its only side not exposed to the water, which is into the o-ring groove created where the surfaces mate. The water itself is pushing the o-ring tight against the mating surfaces, locking itself out so it cannot enter the other side. The greater the pressure, the better the seal. This is how an o-ring seals! Rather simple and ingenious, and quite effective. How Do I Care for O-Rings? As you may have reasoned, o-rings must be free of dirt and debris to work. Any foreign material that compromises the o-ring being squeezed into the o-ring groove will allow water to enter. This is bad. Fortunately, its very easy to maintain the integrity of this seal by simply inspecting, cleaning and lubricating the o-rings when required.