The position of the three medallions:
-Lobby(Entrance): Inside the corner of the reception table(the white one)
-Garden: Inside one of the tall grasses(It was designed to be found with a metal detector)
-Canteen: Between the two lockers near the electronic(Big red door) door on the second floor

Hope this helps!

Position of the valves:
(Tips: All directions are based on the view from the main entrance to the teaching building.)
-Classroom spot(Teaching Building): Second floor, corridor on the left hand side, second room, inside the lowest level of the locker
-Desk spot(OFTEN MISSED): Second floor, the end of the middle corridor, inside the desk(You have to turn around to see it, it's inside the desk)

Hope this helps, if you found that the position of the valves are tricky, I apologize. However, currently it is not a good decision to change the position of props.

For those who may wonder where the finger is, though it's the key for the door at the beginning lobby, it's actually the final goal for all the puzzle in the teaching building, garden and the dining hall. You can find it by unlocking the golden security box in the gym(3rd floor of dining hall building).