The pressure and temperature flowing through the medium inside the valve act as an energy-driven valve to work automatically, and no external power supply and secondary instrument are required. The self-operated regulating valve uses the feedback signal (pressure, differential pressure, temperature) at the output of the valve to transmit the valve to the actuator to drive the valve flap to change the opening of the valve to achieve the purpose of regulating pressure, flow and temperature. This regulating valve is divided into two types: direct acting and indirect acting.
The direct acting type is also called spring loaded type, and its structure has elastic elements such as: spring, bellows, bellows type warm pack, etc., which utilizes the principle of balance between elastic force and feedback signal.
The indirect acting regulating valve adds a pilot (pilot valve) which amplifies the feedback signal and then drives the main valve flap to move the valve opening to change the valve opening.
In the case of a pressure regulating valve, the feedback signal is the outlet pressure of the valve and is introduced into the actuator through the signal tube.
In the case of a flow regulating valve, there is an orifice plate (or other resistance device) at the outlet of the valve to extract the differential pressure signal from both ends of the orifice plate into the actuator.
In the case of a temperature regulating valve, the outlet of the valve has a temperature sensor (or a warm pack) that drives the actuator through thermal expansion and contraction of the medium in the temperature sensor.
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