Valves with 3 ports; inlet, outlet (cylinder) and exhaust. They are generally used to operate spring return cylinders or as pilots for larger diaphragm or piston operated valves
A 3-way directional control solenoid valve has 3 pipe connections: the cavity port, the body orifice port and the stop port. It has 2 orifices: the body orifice and the stop orifice, one of which is always open. This allows for 2 paths of flow.