Selectors (multiposition valves) step incrementally through continuous revolutions, instead of switching back and forth like two position valves. (Selectors step bi-directionally with microelectric and universal actuators.) The preload design allows the rotor to be inspected or replaced without taking the valve off the actuator. Valves ordered with a microelectric actuator are permanently aligned.
Valco selectors are available in five lower pressure flowpaths typically used in gas chromatography applications (most also available with the built-in purge feature), and two high pressure flowpaths suitable for high performance liquid chromatography.
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.
SC selectors are similar to SDs. They select one of 4 to 16 streams, with the selected stream flowing from the valve outlet to a sample valve, pressure sensor, detector, column, etc. The non-selected streams flow to a common outlet, instead of being dead-ended as in the SD model.
SD and SC valves select and isolate one of 4 to 16 streams, with the remainder dead-ended in the SD and flowing to a common outlet in the SC. The SF selector is similar, but carries the evolution a step further with the non-selected streams flowing through individual outlets.
ST selectors are used for multi-column, multi-sample, or multi-trap operations, and are available for use with 4 to 16 loops, or positions. Valves can be ordered with matched loops already installed.