The regulating valve is a key piece of equipment used to accurately control the flow of fluids (gas, liquids, or steam) in the industrial process. Its working principle is to adjust the flow rate by changing the circulation cross-section between the valve core and the valve seat. The following is a step-by-step explanation of its core working principle:
Basic structure
The regulating valve usually consists of two parts: the actuator and the valve body:
Actuator: Receives control signals (such as electric 4-20mA, pneumatic 0.2-1.0bar) and drives the valve stem movement.
Valve body: including the valve core, valve seat, and flow channel, and the position of the valve core determines the flow rate and flow rate.
Workflow
1. Signal input:
The controller (such as PLC or DCS) sends control signals to the actuator according to the process requirements.
2. Actions of the executive mechanism:
Electric valve: the motor drives the valve stem to move up and down.
Pneumatic valve: the air source pressure pushes the piston or film to drive the valve stem.
3. Valve core position adjustment:
The valve stem drives the valve core (such as ball valve, butterfly valve, sleeve and other structures) to move up and down, changing the opening between the valve core and the valve seat.
4. Flow adjustment:
Increase the opening degree → increase the circulation area → increase the flow rate;
Decrease in opening degree → decrease in circulation area → decrease in flow rate.
Key design factors
● Traffic characteristics:
Describe the curve of the relationship between opening and flow; common types:
Linear characteristics: the opening is directly proportional to the flow rate.
Equal percentage characteristics: every time the opening is increased by the same percentage, the flow rate changes by the same percentage (suitable for fine adjustment of small opening degree).
Fast opening characteristics: the flow rate changes greatly when the opening is small, which is suitable for fast response.
● Valve core type:
Through single-seat valve: small leakage, suitable for small flow.
Straight-through double-seat valve: large pressure difference is allowed, but the leakage volume is high.
Sleeve valve: good stability under high pressure difference, suitable for noise control.
Angle valve: suitable for high viscosity or particle-containing media.
● Selection of executive agency:
Pneumatic: fast response, inherently safe, needs a gas source.
Electric: Convenient signal transmission, suitable for remote complex control.
Self-reliant regulating valve
No external energy is required, and the medium's own pressure changes are automatically adjusted:
Self-supporting pressure regulating valve: senses the downstream pressure through the diaphragm, and adjusts the opening to maintain the set value.
Self-powered flow regulating valve: built-in flow sensor, dynamic balance flow.
Application scenario
Process control: closed-loop control of temperature, pressure, liquid level, and other parameters.
Safety protection: prevent overpressure or overheating (such as a safety valve).
Energy management: optimize the efficiency of fluid transportation and reduce energy consumption.
Sum up
The regulating valve drives the movement of the core through the actuator to change the cross-sectional area of the fluid channel, so as to achieve precise control of the flow. Its design needs to comprehensively consider fluid characteristics, pressure difference, control accuracy and process requirements. It is an indispensable terminal executive component in the automation control system.
