Industrial Control Valve: Crucial Parts and the Selection Process
An industrial control valve is utilized in applications that require the control of flow, temperature, pressure and liquid level. It can also modify the fluid or gas flow rate in the process system. A control valve performs this function by assuming the closing or opening position, in response to the controller's signals that are monitored and received by corresponding sensors.
Industrial control valve units have three major parts, which can come in various designs and materials of construction. These main parts are the actuator, the positioner and the valve body. The opening or closing of control valves is typically done automatically by an actuator, which is controlling device. Actuators used for an industrial control valve can be hydraulic, electric, and pneumatic. Actuators can also fall into two classifications, which are direct acting and reverse acting. A direct-acting actuator pushes down when the signal is increasing, while the reverse-acting actuator pushes up upon detecting an increased in the signal. The valve's positioner is the mechanism responsible for closing or opening the actuator via electric or pneumatic signal.
Since industrial control valve models operate through a certain power source, safety concerns always emerge when power is cut off. This is why a number of control valve for various applications possess the fail-safe mode feature. This safety feature varies according to the valve application. About 80% of the industrial applications require a fail closed mode, while others need their valves to fail open or fail in place in the event of power loss. For heating applications, the valve is expected to fall closed while cooling applications require the valve to fall open during power failure. When a control valve is in the fail position, it will not receive or execute command from an external signal.
Industrial control valve units are engineered to offer efficient performance under the most challenging and rigorous industrial environment, including manufacturing and processing operations. The proper selection of a control valve for specific applications needs a systematic method. Prospective operators should first understand the process loop and the different product line available. The selection process must include factors like materials of construction, valve size, actuator size and action, and other characteristics.
The materials used to construct an industrial control valve are usually based on the physical and chemical characteristics of the process product as well as the process line's operating temperature, flowing pressure. Control valves with brass, or cast iron bodies are generally appropriate for low temperature and low pressure water or steam application. Steel is more suitable for applications with high temperature or flammable fluid like lube oil, while stainless steel is effective in tolerating corrosive products. When it comes to valve size, choosing the correct dimensions will have a direct effect on the control valve's performance in the process environment. Determining the connecting pipe's size and the Cv to address the flow requirements are the two main considerations when sizing a control valve. In some situations, there will more than one valve model that is acceptable; and the decision may ultimately depend on the pricing or other personal preferences.
