Fisher® YD and YS three-way cage-guided valves are designed for throttling or flow-switching (on-off) service. The YD balanced valves are for general converging (flow-mixing) and diverging (flow-splitting) service. They are available in standard and high-temperature versions. The YS unbalanced valves are for general converging service. When used in diverging service, YS valves are recommended for on-off applications only.