1) Where friction is large and precise positioning is required. For example, high temperature and low temperature control valves or control valves with flexible graphite packing;
2) Where the response speed of the regulating valve needs to be improved in a slow process. For example, the regulation system of temperature, liquid level, analysis and other parameters.
3) Where the output force and cutting force of the actuator need to be improved. For example, single seat valve with DN ≥ 25 and double seat valve with DN ＞ 100. The pressure drop at both ends of the valve △ P ＞ 1MPa or the inlet pressure P1 ＞ 10MPa.
4) In the operation of split range control system and control valve, it is sometimes necessary to change the air opening and air closing forms.
5) Where the flow characteristics of the regulating valve need to be changed.
