Scubapro MK17 EVO 2 First Stage YokeThe new MK17 EVO 2, Yoke is a sealed diaphragm first stage with a dry chamber based on a twin spring layout and two HP ports at 15 degree angle to make hose routing easier. 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. Best Cold Water ScubaPro MK17 EVO Review