The core differences and working principles between safety valves and control valves

Safety valves and control valves are control valves with completely different functions in industrial fluid systems. The core difference lies in the fact that safety valves are safety protection valves (passive action, preventing overpressure), while control valves are process control valves (active regulation, precise parameter control). Their working principles, design purposes, and actuation methods are fundamentally different, as detailed below:

I. Core Definition and Design Purpose (Essential Difference)

Safety valves are safety relief devices whose sole purpose is to prevent the pressure within a system (container, pipeline, equipment) from exceeding the design maximum allowable pressure, thus avoiding safety accidents such as equipment rupture and explosion caused by overpressure. They are the last line of defense for system safety and have no process regulation function.

Control valves are process control valves whose core purpose is to actively and precisely adjust process parameters such as pressure, flow rate, temperature, and liquid level within the system according to process requirements, ensuring that the system always operates under the set process conditions. They are the "regulator" in process production and have no safety relief function.

II. Working Principle (Core Differences)

Safety Valve: Passively triggered, overpressure relief, reseating after pressure recovery. The opening pressure of the safety valve is the set pressure (pre-calibrated according to the equipment design pressure and cannot be arbitrarily adjusted). Under normal operating conditions, when the system pressure is less than or equal to the set pressure, the valve disc is pressed tightly against the valve seat by the force of the spring/counterweight, and the valve is completely closed with no leakage of the medium. When the system pressure exceeds the set pressure due to a fault (such as medium pressure buildup or excessive heating), the upward thrust of the medium on the valve disc is greater than the downward force of the spring/counterweight, and the valve disc is pushed open. A large amount of medium is rapidly released through the valve port, causing the system pressure to drop rapidly. When the system pressure drops to the reseating pressure (below the set pressure), the force of the spring/counterweight is again greater than the thrust of the medium, and the valve disc automatically reseats and closes, restoring the system to normal sealing. The entire process requires no manual/automatic intervention and is entirely passively triggered by the system pressure.

Supplement: Safety valves are classified by power source into spring-loaded (most commonly used), counterweight, and pilot-operated types. The core principle of all of them is "pressure difference triggering action".

Control Valve: Active regulation, continuous/intermittent action based on signals, precise parameter control. The control valve consists of an actuator (pneumatic/electric/hydraulic) and a valve body. It receives electrical signals (4-20mA)/pneumatic signals (0.02-0.1MPa) from the control system. The actuator drives the valve stem, which in turn moves the valve disc (valve core) up and down/rotates, changing the flow cross-sectional area of the valve orifice. Changes in the flow cross-sectional area directly alter the medium's throughput, thus regulating process parameters such as flow rate, pressure, and temperature. For example, opening the valve orifice increases the medium flow rate and decreases the system pressure; closing the valve orifice decreases the medium flow rate and increases the system pressure. The entire process is controlled automatically or manually. It can be continuously and steplessly adjusted according to process requirements (e.g., linear change in valve opening from 10% to 90%), or intermittently switched on and off, always precisely adjusting around the process setpoint. It has no "leakage" design, ensuring no significant medium loss under normal operating conditions.