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.
High pressure SD selectors are made of Nitronic 60, with a rotor made of Valco E, a polyaryletherketone/PTFE composite. Valves are rated for 5000 psi liquid at 75°C.
Valves can be actuated manually or automated with pneumatic or electric actuators. HPLC valves don't usually require a standoff, but they are offered, in lengths of 2", 3" 4", and 6".