See all products of ROBOCAL™ Automatic (up to 1.75 SCFM) ROBOCAL™, Automatic air vent ROBOCAL™, Automatic air vent with service check valve ROBOCAL™, Automatic air vent with service check valve/hygroscopic cap ROBOCAL, Automatic air vent (1⁄4" straight thread) ROBOCAL, Automatic air vent (⅜"-½" straight thread)