How the control valve works

Electric actuated control valves are used for process automation and in building engineering systems (heating, ventilation, cold and hot water supply). The control valve shuts off the pipeline, opens it, or restricts the water flow by partially closing the passage. The valve operates automatically based on signals from the control system.

Control valves are typically used together with electric actuators connected to an automation system controller. In industrial and process applications, control valves may be operated by pneumatic or hydraulic actuators.

How a Control Valve Works

The automation system measures a controlled parameter (room temperature, water flow, water temperature, or another parameter) and, if it deviates from the setpoint, sends a signal to the electric actuator to open or close the control valve. The actuator receives the signal and moves the valve disc to the position determined by the automation system.

The change in flow within the pipeline where the control valve is installed should influence the parameter monitored by the automation system. More details on control valve installation schemes can be found in the 'Installation Schemes' section.

Optimal operation of a control valve, which must periodically operate in a partially closed position, is only possible if a stable pressure differential between its inlet and outlet is maintained. Differential pressure stabilization ensures the valve operates according to its hydraulic characteristic (linear, logarithmic, or parabolic – more details in the 'Control Valve Characteristics' section). This is why control valves are usually installed together with differential pressure controllers. The working principle of an electric actuated control valve paired with a differential pressure controller is explained on this page.

The position of the control valve disc depends on the signal received by the electric actuator from the automation system and the availability of power supply.

All types of control valves can be classified based on their function: those that restrict, mix, or divide the flow of the working medium. Valves that restrict water flow are called two-way valves, while mixing valves are four-way and three-way valves.

Two-Way Control Valve

A two-way control valve has two flanges for pipeline connection and is designed to regulate water flow. Depending on the disc design, valves are classified as seat, ball, or gate valves. Gate and seat control valves require actuators with linear stem movement, while ball control valves are fitted with rotary electric actuators.

Two-way control valves are used for controlling heat exchangers in domestic hot water systems and independent heating systems, managing mixing processes in heat substations with dependent connections to the heating network, and as actuators for indirect-acting flow, pressure, or differential pressure regulators.

Control Valve Operation in Case of Power Loss

In the event of a power failure, some valves remain in the position where the disc was when the power was lost, while others may fully open or fully close. The valve’s behavior in case of a power outage depends on the electric actuator and the valve’s design. Selecting a valve and actuator with the appropriate fail-safe position according to automation system requirements is determined during the system design phase.

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