When should I use a linear or equal percentage valve?
A summary table shows the characteristics of linear and equal percentage valves below:
| Characteristic | Linear Valve | Equal Percentage Valve |
|---|---|---|
| Flow vs. Stem Position | Flow changes proportionally with stem movement. | Flow change is small at low openings and increases exponentially. |
| Best Used When | System pressure drop is constant. | System pressure drop varies significantly. |
| Application Types | Liquid level control, steam injection, direct pressure control. | Steam, gas, and temperature control applications. |
| Process Gain | Constant throughout the valve stroke. | Low at small openings, increases as the valve opens. |
| Flow Demand Changes | Small and predictable. | Large variations. |
| Control Sensitivity | Provides steady control at all positions. | Offers fine control at low flow, large impact at high flow. |
| Preferred Use Case | Liquid systems with linear response. | Nonlinear processes where flow increases exponentially. |
Rule of Thumb:
- Linear valves should be used for systems showing consistent operation and low pressure changes.
- The application of equal percentage valves becomes necessary when systems deal with changing loads and significant flow variations.