The new D420 features an all-new balanced valve located within the housing, supported by an all-metal construction. This valve, called the Progressive Flow Control Valve, is able to provide abundant air flow for best performance, ensuring smooth, natural breathing comparable to what you might experience on the surface. The uniquely shaped fiberglass-reinforced nylon case is ultra-strong and allows you to attach the whip on both the left and right sides, ensuring maximum cordage flexibility. The new dive/pre-dive system includes a case switch with a finger guard to adjust the direction of airflow out of the valve. The high-efficiency purge button is a jewel of technology based on a brand new prototype that also gives the D420 uniqueness in appearance. Combined with the very light and compact MK19EVO with its watertight system, its pressurized chamber as well as the rotating turret with intuitive LP port, they form a particularly formative delivery system in cold waters or during the most demanding dives, often encountered by technical divers. These peculiarities make the MK19EVO/D420 combination more technological than the MK25EVO/D420 combination, fully satisfying both the most hardened divers and enthusiasts of the SCUBAPRO brand.