April 26, 2013
A 4-way stopcock allows for 360° of rotation and has the states (shown below) for each of the four available positions. A 3-way stopcock has only three positions and has the first three states shown below.
In the first state, liquid flows between points A and B.In the second, it flows between points A and C.In the third, it flows between points B and C.In the fourth state (4-way only), it flows between all three points.
3-way and 4-way stopcocks are sold in the popular kit 14011. They can also be bought separately: