2-way: One inlet and one outlet, and are used to permit and shut off
fluid flow. The two types of operations are "Normally Closed" and
3-way: These valves have three pipe connections and two orifices. When
one orifice is open, the other is closed and vice versa. They're commonly
used to alternately apply pressure to an exhaust pressure from a valve
actuator or a single acting cylinder. These valves can be normally closed,
normally open or universal.