Standard Namur valves are assembled for 5 port operation. A valve may be converted to operate using only 3 ports. To convert, remove the 5/16"-32 plug on the side of body and install same plug into threaded bottom port. When port 2 is plugged, the standard NSO2 works as a normally open "NO" valve using port 4. Pressure in port 1 is directed to port 4 when the solenoid is de-energized. When the solenoid is energized port 4 is connected to exhaust port 5, port 1 is blocked. To configure valve for a normally closed "NC" operation, switch the operators located on each end and flip the internal spool and/or spring. Or order a valve with the operators pre-swapped like a NOS2. In this reversed configuration, port 4 is connected to exhaust port 5 when the solenoid is de-energized. When the solenoid is energized port 1 is directed to port 4.