The MK17 EVO DIN300 First Stage is a balanced diaphragm design engineered for harsh environments, including ice-cold or polluted water. Its dry ambient pressure chamber prevents water entering the first stage mechanism, and its balanced technology maintains consistent performance across cylinder pressures and depths. It has two opposite high-pressure ports, allowing the first stage to be mounted pointing up or down so gauges can be positioned on either side, and four low-pressure ports, two of them high-flow, which deliver around 15% more air than standard ports. It is sold separately from a second stage in a DIN300 fitting.