The MK17 EVO is SCUBAPRO's premium high performance balanced diaphragm first stage. Engineered specifically for cold water and harsh environments, its internal components are completely sealed off from the elements so neither water nor pollution can get inside the chrome-plated marine grade brass body to foul the mechanism. This total sealing system also allows for a dry ambient pressure chamber which works to prevent freezing, provides better protection and improves performance, ensuring trouble-free operation no matter how cold or murky the water gets.