Self-acting control valve

A self-acting control valve relies on the pressure and temperature of the medium flowing through it as the energy source to drive the valve to operate automatically, without the need for an external power supply or secondary instruments. These self-acting control valves utilize feedback signals from the valve’s output side (pressure, pressure difference, temperature), which are transmitted via signal tubes to the actuator in order to drive the valve disc and adjust the degree of opening of the valve, thereby achieving regulation of pressure, flow rate, and temperature. Such control valves are further divided into direct-acting and indirect-acting types. The direct-acting type, also known as the spring-loaded type, features elastic elements such as coil springs, bellows, or bellows-type thermocouples in its structure, and operates on the principle of balancing elastic force with feedback signals. In indirect-acting control valves, an actuator (pilot valve) is added; this actuator amplifies the feedback signal, and then through the actuating mechanism, it drives the valve disc to move in order to change the valve opening degree. In the case of a pressure control valve, the feedback signal is the outlet pressure of the valve, which is transmitted to the actuator through a signal line. In the case of a flow control valve, there is a orifice plate (or some other flow resistance device) at the valve’s outlet; the pressure difference across this orifice plate is used to generate a signal that is fed to the actuator. In the case of a temperature control valve, there is a temperature sensor (or thermocouple) at the valve’s outlet; the expansion and contraction of the fluid inside this sensor drive the actuator.

The self-acting control valve operates on a principle similar to that of safety valves. Each pump in our company is equipped with a self-acting control valve that serves as a safety mechanism

I have used a self-acting temperature control valve: the sensing element, in the form of a therm bulb, is attached to the water outlet, and a medium is used through pipelines to adjust the opening degree of the temperature control valve, thereby controlling the flow rate of the heating steam and thus regulating the temperature of the water being heated.