What are the three types of control valves?
Control valves regulate the flow of liquids or gases by adjusting the position of the internal mechanism (such as a valve trim piece, a valve flapper). The shape of the clamp determines how the flow changes according to the movement of the valve stem. Here is a detailed description of the three types of valve you mentioned:
1. On-Off Valve (Quick Opening Characteristic)
Flow and Valve Position:
In valves with an on-off characteristic, the majority of the flow change occurs at the beginning of the valve movement. Nearly maximum flow is achieved with minimal stem movement.
Applications:
On-off valves are used in applications that require rapid access to high flow rates, such as on/off control systems. They are not well-suited for precise control in intermediate positions.
2. Linear Valve Design (Linear Characteristic)
Flow and Valve Position:
In a linear valve, the flow increases in direct proportion to the valve position. For example, when the valve is 50% open, the flow rate is approximately 50% of the maximum flow.
Applications:
Linear valves are preferred in situations where consistent and predictable flow control is required. They are used in pressure control systems or applications where precise flow adjustments are critical.
3. Equal Percentage Valve (Proportional Parabolic Characteristic)
Flow and Valve Position:
In an equal percentage valve, each increment in valve movement results in a percentage increase relative to the previous flow rate. When the valve is slightly open, flow changes are minimal, but as the valve opens further, the flow rate increases rapidly.
Applications:
This type of valve is ideal for systems with wide operating ranges or pressure variations, where both low and high flow rates need to be carefully managed.
Summary:
Quick Opening: Ensures rapid flow increase for quick response, used in on/off applications.
Linear: Provides proportional flow changes, suitable for applications requiring precise control.
Equal Percentage: Starts with slow flow changes but increases rapidly as the valve opens; ideal for variable conditions.