# Step-by-Step Solution and Explanation ## **Problem Recap** - **Flow controller** is **reverse acting** (increasing flow setpoint decreases output signal). - **Output signal range**: .2 to 1. bar pneumatic. - **Two control valves**: - **V1 (large range valve):** Handles majority of flow. - **V2 (small range valve):** Only operates in the first 25% of controller output. - **Requirement**: V2 operates only for the first 25% of signal, then V1 takes over. - **Valves have opposite failure actions** (one fails open, one fails closed). --- ## **Step 1: Understand Valve Action and Failures** - **Reverse acting controller**: As flow increases, output signal decreases. - **Valve failure action**: - **Large valve (V1):** Fail open (FO) - **Small valve (V2):** Fail closed (FC) --- ## **Step 2: Signal Splitting Concept** To achieve sequential control (V2 for first 25% of signal, V1 for the remaining 75%), **signal splitters** and **valve positioners** are required. - **Signal splitter** divides the controller output signal range into two parts: - First range (.2 to .4 bar) to V2 - Second range (.4 to 1. bar) to V1 --- ## **Step 3: Valve Positioner Settings** ### **Small Valve (V2)** - **Operates from .2 to .4 bar** (25% of .2–1. bar range) - **Valve positioner** should be set so V2 goes from fully open (at .2 bar) to fully closed (at .4 bar). - **Action**: Since controller is reverse acting, V2 should be **air-to-close (fail open)**. ### **Large Valve (V1)** - **Operates from .4 to 1. bar** (remaining 75% of range) - **Valve positioner** should be set so V1 starts to open at .4 bar and is fully open at 1. bar. - **Action**: V1 should be **air-to-open (fail closed)**. --- ## **Step 4: System Design** - **Install a pneumatic signal splitter** after the controller to divide the .2–1. bar signal. - **Set valve positioners** as follows: - **V2 (small valve):** - **Signal range:** .2–.4 bar - **Action:** Air-to-close (fail open) - **Positioner:** Full travel between .2–.4 bar - **V1 (large valve):** - **Signal range:** .4–1. bar - **Action:** Air-to-open (fail closed) - **Positioner:** Full travel between .4–1. bar **Note:** When controller output is .2–.4 bar, V2 modulates while V1 remains closed. When output exceeds .4 bar, V2 is fully closed and V1 begins to open. --- ## **Step 5: Final Answer (Summary Table)** | Valve | Signal Range (bar) | Action | Failure Action | Positioner Setting | |------------|--------------------|----------------|----------------|------------------------| | Small (V2) | .2–.4 | Air-to-Close | Fail Open | Full travel in .2–.4 | | Large (V1) | .4–1. | Air-to-Open | Fail Closed | Full travel in .4–1. | --- ## **System Schematic** **[Signal Splitter]** ``` Controller Output (.2–1. bar) | ------------------------ | | .2–.4 bar .4–1. bar (to V2) (to V1) ``` --- ## **Conclusion** - **Use a signal splitter and valve positioners.** - **V2 (small valve):** Air-to-close, fail open, operates .2–.4 bar. - **V1 (large valve):** Air-to-open, fail closed, operates .4–1. bar. - This setup meets the requirement: V2 controls low flow, V1 controls high flow, with appropriate fail-safe actions. --- ### **If you need a diagram or further explanation, let me know!**

# Step-by-Step Solution and Explanation ## **Problem Recap** - We are dealing with a **reverse acting flow controller**. - **Output signal range**: 0.2 to 1.0 bar pneumatic. - **Two control valves**: - **V1 (large range valve)**: Handles majority of flow. - **V2 (small range valve)**: Operates in the first 25% of controller output. - **Valve failure actions**: - V1 fails **open**. - V2 fails **closed**. --- ## **Step 1: Understand Valve Action and Failures** - **Reverse Acting Controller**: An increase in flow setpoint decreases the output signal. - **Valve Actions**: - V1: Fail open - V2: Fail closed --- ## **Step 2: Signal Splitting Concept** - **Signal Splitter** is required to divide the output signal: - **First range**: 0.2 to 0.4 bar → V2 - **Second range**: 0.4 to 1.0 bar → V1 --- ## **Step 3: Valve Positioner Settings** ### **Small Valve (V2)** - **Signal Range**: 0.2 to 0.4 bar (25% of total range) - **Action**: Air-to-close (because it should fail open) - **Positioning**: Fully open at 0.2 bar, fully closed at 0.4 bar. ### **Large Valve (V1)** - **Signal Range**: 0.4 to 1.0 bar (remaining 75%) - **Action**: Air-to-open (because it should fail closed) - **Positioning**: Starts to open at 0.4 bar and fully opened at 1.0 bar. --- ## **Step 4: System Design** 1. **Install a pneumatic signal splitter** after the flow controller. 2. **Set valve positioners**: - **V2 (small valve)**: - **Range**: 0.2 to 0.4 bar - **Action**: Air-to-close, fail open - **Positioner Setting**: Full travel between 0.2 and 0.4 bar. - **V1 (large valve)**: - **Range**: 0.4 to 1.0 bar - **Action**: Air-to-open, fail closed - **Positioner Setting**: Full travel between 0.4 and 1.0 bar. **Operation**: - From 0.2 to 0.4 bar: V2 modulates while V1 remains closed. - Exceeding 0.4 bar: V2 is fully closed, and V1 begins to open. --- ## **Step 5: Final Answer (Summary Table)** | Valve | Signal Range (bar) | Action | Failure Action | Positioner Setting | |------------|--------------------|----------------|----------------|------------------------| | Small (V2) | 0.2–0.4 | Air-to-Close | Fail Open | Full travel in 0.2–0.4 | | Large (V1) | 0.4–1.0 | Air-to-Open | Fail Closed | Full travel in 0.4–1.0 | --- ## **System Schematic** **[Signal Splitter]** ``` Controller Output (0.2–1.0 bar) | ------------------------ | | 0.2–0.4 bar 0.4–1.0 bar (to V2) (to V1) ``` --- ## **Conclusion** - A **signal splitter** and **valve positioners** are necessary. - **V2** operates between **0.2–0.4 bar** with air-to-close action. - **V1** operates between **0.4–1.0 bar** with air-to-open action. - This setup ensures V2 controls low flow and V1 controls high flow, satisfying operational requirements and safety considerations. --- ### **If further clarification or illustrations are needed, please ask!**