Major control and isolation valves in traditional fire sprinkler systems are typically large gate valves of the "Outside Screw and Yoke" (OS&Y) type, sometimes called "rising stem" valves. The state (open or closed) of this type of valve can be determined at a glance, and specialized locks and alarm sensors may be attached to restrict and monitor the settings of these valves, which are critical to overall building safety. Newer systems may use butterfly valves instead of some or all possible OS&Y valves.
