These 3-port solenoids are a high performance electronic valve allowing precise control of your LoudValve. You can use a simple switch with these Normally Closed solenoids for a way to shut off the boost/vacuum signal, the filter allows pressure to bleed off making the loudvalve close instantly when de-activated.
Another use would be to use an output from you ecu or standalone EMS to control at what boost pressure the valve will open/close. These solenoids come with brass barb fittings and filter.