SD valves select one of 4 to 16 dead-ended streams, directing it through the valve outlet to a sample valve, pressure sensor, detector, column, etc. The same configuration can also direct one stream to a number of outlets for fraction collection.
Low pressure SD selectors are made of Nitronic 60, with a rotor made of Valco E, a polyaryletherketone/PTFE composite. Valves are rated from 100 to 400 psi gas and 75° to 200°C, depending on the fitting size and number of positions.
Valves can be actuated manually or automated with pneumatic or electric actuators. GC valves usually require a standoff - an extension between the valve and actuator which allows the valve to be mounted in the heated zone while the actuator or handle remains outside at ambient temperature. Standoffs are available in lengths of 2", 3" 4", and 6".