The SV2 is designed to limit splashed water from entering the breathing tube, by combining the Scupper Valve lower section with the sleek looking SV2 Semi-Dry top. SV2 is the perfect snorkel for rough or choppy water conditions. The SV2 includes a Scupper Valve lower section with a sleek semi-dry top. The SV2 semi-dry top employs horizontal vents engineered to diffuse splashed water that would normally freely enter the snorkel top. The small gaps between the vanes of the vent restrict water speed and droplet size and permit most of the splashed water to exit the special vents without entering the breathing tube. The end result is less water in your snorkel. The SV2 is perfect for rough or choppy water conditions.SV2 with Semi-Dry Top The SV2 combines the same Scupper Valve lower section with the sleek and effective SV2 Semi-Dry top. The SV2 Semi-Dry top horizontal vents (1) are engineered to diffuse splashed water that would normally freely enter the snorkel top. The small gaps between the vanes (2) of the vent restrict water speed and droplet size and permit most of the splashed water to exit the special vents (3) without entering the breathing tube. Thus, you get less water in your snorkel. The SV2 is the perfect answer for rough or choppy water conditions. The Scupper Valve (SV) design is self-draining and delivers crisp, effortless clearing. Posi-lock flex retainer secures flex section and mouthpiece. (1) Dual silicone mouthpiece prevents over-clenching of teeth that would restrict air flow.( 2) Rotational mouthpiece with ratchet indicators. (3) SV1 has a conical flared top for high performance breathing. SV2 Semi-dry top is designed to limit splashed water from entering the breathing tube.