Ford fit a recirculating valve to stop the noise when the Cosworth was realesed to the public, As people didnt like the "Chatter" that was heard. (Be it not alot on 9psi but was still there)

A dump valve/ recirculating valve isnt really needed till you go T4 or higher on loads of boost.

I dont run one at all on mine and its fine. I also didnt run one when my T3 was boosting 27psi for 10,000mile, took that off and it was perfect