The top is the engine vacuum from the intake, next one down is the parking brake release actuator, followed by a hose that goes to the vacuum storage tank, and the bottom goes to the AC system. See below:
Now I'm not sure but I believe that the vacuum check valve is at the bottom just for the AC system. Can anyone verify this, because I can't find a replacement for this part so I'm thinking of using a splitter for the top 2 and use a standard check valve for the bottom one. Would this work?