The Vacuum Flange Insert (VI) is a vacuum check valve designed to fit between ISO/NW/KF/QF vacuum flanges designed in accordance with DIN 28403, DIN 28404, ISO 1609, and ISO 2861. It is both a centering ring and a check valve. The compact design requires no additional space in the line. Its size makes it extremely economical when compared to full-bodied valves. The VI valve can also be used as a low-pressure relief valve under either positive or vacuum conditions by using the desired spring setting.