What is the difference between 3/2 and 4/2 solenoid valve

Field Instrumentation
1

Explain how a 3/2 SOV is different from a 4/2 SOV

2

3/2 SOV

3 port 2 output

4/2 SOV

4 PORT 2 OUTPUT AND ONE COMMON EXHAUST

The number of port connections with 2-way actions, open and close. Both must have port connections for exhaust. Internal valve operation for port connection can be determined through symbol markings and even w/o diag. by actual simulation