The MK17 EVO is a 1st stage with a balanced airflow membrane that provides a good constant flow of air regardless of your depth or bottle pressure. The MK17 EVO is one of Scubapro's high-performance 1st stages and is therefore completely sealed off from external elements and specifically manufactured to operate in cold and harsh conditions. Totally sealed means that no dirt can get into the regulator and therefore it can be dived in really dirty and cold conditions without problems. Constructed in high quality chrome plated brass to prevent acid damage and rust. The MK17 EEVO has 2 HP ports positioned opposite each other for easy placement of pressure gauges and 4 LP ports that give you the freedom to position your primary air source and octopus as you wish.