Quick Opening Characteristics • Used for frequent on-off service. • Used for processes where "instantly" large flow is needed (i.e. safety systems or cooling water systems. Two rules of thumb for choosing the right flow characteristic 1. If most of the pressure drop is taken through the valve and the upstream pressure is constant, a linear characteristic will provide better control. 2. If the piping and downstream equipment cause significant resistance to the system, equal percentage will provide better control. ************