| Seven Selection Tips |
| 1 | Define the service conditions | Record the medium, specific gravity (SG), temperature, pressure, solids content, and chemical concentration before selecting the valve. | Clean water has an SG of approximately 1.00 at normal ambient temperature. PVC pressure capability generally decreases as temperature rises. | Confirm chemical compatibility and apply the temperature derating stated in the applicable PVC pressure-rating data. |
| 2 | Choose the correct DN size | DN is the nominal size designation; it is not necessarily the measured inside diameter. Verify the pipe outside diameter, wall thickness, and flange drilling. | Common nominal sizes include DN50, DN80, DN100, DN150, DN200, DN250, and DN300. | Match the valve DN to the piping system and avoid reducing the valve size solely to lower purchase cost, because velocity and pressure loss may increase. |
| 3 | Calculate the required Cv | For liquids: Cv = Q × √(SG ÷ ΔP), where Q is in US gal/min and ΔP is in psi. | Example: 80 m³/h water equals approximately 352 US gal/min. At ΔP = 0.50 psi and SG = 1.00, required Cv ≈ 498. | Select a valve whose Cv at the intended operating angle exceeds the calculated requirement, while avoiding an excessively oversized valve. |
| 4 | Check the normal opening position | Butterfly valve Cv changes significantly with disc angle. The available Cv must be checked at the actual operating position, not only at full open. | A normal control position of approximately 30–70% open is commonly preferred for stable adjustment; exact limits depend on the valve characteristic. | If the valve operates almost closed, consider a smaller DN or a valve designed specifically for throttling service. |
| 5 | Size the actuator by torque | Required actuator torque should cover breakaway, running, seating, and unseating torque under the maximum differential pressure. | A practical engineering allowance is commonly 1.25–1.50 × the maximum specified valve torque for clean service, subject to the valve manufacturer’s data. | Example: if the maximum valve torque is 80 N·m, specify an actuator with at least 100–120 N·m available at the required operating conditions. |
| 6 | Select the correct actuation mode | Choose manual, electric, or pneumatic actuation according to cycle frequency, control accuracy, available utilities, and required failure position. | Pneumatic actuators are suitable for frequent cycling; electric actuators are useful where compressed air is unavailable. Fail-open and fail-closed functions require additional design review. | Confirm actuator output torque at the minimum supply voltage or air pressure, not only the nominal rated value. |
| 7 | Verify installation and pressure limits | Check flange standard, face-to-face dimension, pressure class, temperature rating, shaft orientation, available clearance, and upstream/downstream installation requirements. | PVC systems may use different pipe and flange standards; incompatible drilling or excessive flange misalignment can damage the valve or liner. | Confirm all dimensional and pressure data against the project specification and the valve’s certified technical documentation before purchase. |
| Illustrative PVC Butterfly Valve Sizing Reference for Clean Water at Approximately 20°C |
| DN | Typical Full-Open Cv Range | Approx. Flow at ΔP = 0.50 psi | Typical Reference Torque Range | Sizing Note |
| DN50 | 100–150 | 16–24 m³/h | 20–35 N·m | Verify the actual Cv curve at the intended opening angle. |
| DN80 | 220–320 | 35–51 m³/h | 35–70 N·m | Use the higher torque value when differential pressure or cycling frequency is high. |
| DN100 | 400–550 | 64–88 m³/h | 60–110 N·m | For an 80 m³/h duty, a Cv near 500 is required at 0.50 psi pressure loss. |
| DN150 | 850–1,200 | 136–192 m³/h | 140–260 N·m | Check pipe support and actuator clearance because valve mass and operating loads increase with size. |
| DN200 | 1,500–2,100 | 240–336 m³/h | 280–500 N·m | Use maximum differential pressure for actuator selection, not average operating pressure. |
| DN250 | 2,400–3,300 | 384–528 m³/h | 500–900 N·m | Review structural loads, flange alignment, and emergency operating requirements. |
| DN300 | 3,500–4,700 | 560–752 m³/h | 850–1,500 N·m | Obtain a certified torque curve and full-open Cv curve before final actuator approval. |
| Engineering note: Cv and torque values in this reference are typical ranges for concentric PVC butterfly valve designs and can vary with disc geometry, liner material, pressure differential, temperature, fluid properties, installation, and opening angle. Final selection must use the certified data for the specific valve configuration. |
