[statik]

That looks like it could be part of the stock boost solenoid setup, but either way you don't need it, you will just run whatever the spring is in the actuator which is around 7-8psi stock. With the solenoid stock SR's run around 9-10 psi I think. The solenoid allows for safety boost(car throws a cell it will run the lowest boost possible, 7psi) and also boost increase with a rom tune or whatever. Most people just get a boost controller and/or upgraded actuator.