This is a pneumatically operated diaphragm valve from the GEMÜ 687 series. The "50" indicates a nominal diameter of DN50. The "SAK" designation refers to a plastic actuator with a stainless steel distance piece. "13/N" specifies the control function (likely Normally Closed) and the actuator size. This valve is designed for controlling aggressive and corrosive fluids. The plastic actuator offers cost-effectiveness and corrosion resistance in certain applications, while the stainless steel distance piece enhances the overall durability of the valve.