What is the purpose of H-valves in diving?

The purpose of H-valves in diving is to allow two regulators to be connected to a single cylinder. This design is particularly useful in emergency situations or when divers require redundancy in their setup. With an H-valve, one regulator can be used for a primary air supply, while a second regulator serves as a backup. This feature provides divers with increased safety, as it ensures that if one regulator fails, the diver can immediately switch to the backup without needing to access another tank. The ability to supply air from two regulators also makes the H-valve a popular choice among technical divers and those engaging in deeper or longer dives, where additional systems might enhance their safety and operational flexibility.

While other options like preventing buoyancy loss, enhancing visibility, and regulating air pressure are important aspects of diving gear and techniques, they do not specifically relate to the functionality or primary purpose of H-valves. These aspects are managed through different equipment and diving practices, but the defining characteristic of the H-valve is its capacity to connect two regulators to a single air source for redundancy and safety.