HKS Racing Bypass valve / BOV , how does it work???

[Digital]

I found this in my tuning-shack:

 

 

I searched and I found it's a HKS Racing Bypass valve.

 

It was once mounted on my 500hp JUN STi when it came from Japan, at that time I replaced it for a SSQV.

 

Can anyone tell me how this BOV works because it has TWO vacuum-nipples where normally a BOV has 1?

 

Thanks!

[Digital]

Found it! Sorry!

 

HKS Standard and Racing Bypass valves are push type valves that utilize calibrated spring pressure and vacuum line pressure to remain closed against the pressurized air in the charge pipe. As the throttle is closed, creating vacuum in the line, combined with the force of the pressurized air in the charge pipe, the bypass valve pushes opens and allows the pressurized air to escape. The HKS Standard Bypass Valves are adequate for the airflow associated with engines producing upwards of 300hp. HKS Racing Bypass Valves function similar to the Standard Bypass Valves, but incorporate an additional pressurized port to aid under severe boost conditions. The Racing Bypass Valve can also be used as a safety "pop-off" valve if the second port is connected to a pressure source that does not see vacuum. For added flexibility and function, HKS Racing Bypass Valves are offered in various adjustable boost pressure ranges that are determine by a specific spring pressure.