Self-operated valves, also known as self-regulating valves or self-actuated valves, are valves that do not require external power or control signals to operate. Instead, they utilize the process fluid's energy or conditions to regulate their own flow, pressure, or temperature. Here's a general overview of how self-operated valves work:

1. Sensing Element: Self-operated valves incorporate a sensing element that responds to changes in process conditions such as pressure, temperature, or flow rate. This sensing element may be a diaphragm, bellows, or piston, depending on the design and application of the valve.

2. Actuation Mechanism: The sensing element is connected to the valve's actuation mechanism, which controls the position of the valve plug, disc, or other closure element. The actuation mechanism may utilize mechanical, hydraulic, pneumatic, or thermal principles to move the valve.

3. Feedback Loop: As process conditions change, the sensing element detects these changes and triggers the actuation mechanism to adjust the valve position accordingly. This creates a feedback loop that allows the valve to automatically regulate its flow, pressure, or temperature based on the desired setpoint or control objective.

4. Balancing Forces: Self-operated valves are designed to balance the forces exerted by the process fluid with the forces generated by the actuation mechanism. This allows the valve to maintain stable operation and achieve the desired control performance without external intervention.

5. Adjustment and Setpoint: Some self-operated valves may include adjustable setpoints or control parameters that allow operators to fine-tune the valve's response to changing process conditions. This adjustment may be done manually or automatically, depending on the design and features of the valve.

6. Applications: Self-operated valves are commonly used in various industries and applications where external power sources or control signals are limited or unavailable. They are particularly suitable for remote or hazardous locations, as well as for applications requiring automatic control of flow, pressure, or temperature.

Examples of self-operated valves include pressure reducing valves, pressure regulating valves, temperature control valves, and flow control valves. These valves are widely used in process industries such as oil and gas, chemical processing, power generation, water treatment, and HVAC systems.

Overall, self-operated valves offer a reliable and cost-effective solution for automatic control and regulation of process conditions, allowing operators to achieve precise control without the need for external power or control systems.