[Peter Johnson]

Originally Posted by viggy96

So does the spring return in a single connect the output to the exhaust port?

A single solenoid valve is also 5-ported. So there are still 2 outputs and 2 exhaust ports. When the coil is energized, one output (A) is connected to its exhaust port (EA) and the other output (B) to the pressurized air (P). When the coil is not energized, the spring in the valve results in the valve being in the other (default) position, thus connecting the other output (B) to its exhaust port (EB) and output A will be connected to the pressurized air (P).

Note this should not be confused with the operation of a spring return cylinder (actuator), which has only a single input port on the cylinder itself. It's possible to use either a "double" or a "single" solenoid with a spring return cylinder.