You can see the tap in the supply pipe, used to de-pressurise the system easily. Approach taken by Cassius and Chaos. We used 12mm. Blue piping on left is fexible polyurethane. White tubing is less flexible, but has a thinner wall, hence a larger bore, 10mm vs 8mm, so has higher gas flow rate.
Threads are also available in a range of sizes.
Piping, fittings and valves are available from any decent Pneumatic Equipment supplier. Designed to operate a double acting cylinder. The solenoid just opens a small valve that causes a bleed from the main supply to open the main valve. Just a 4mm adapter. Diagram showing the flow of gas through a five port valve in it's two states.