Why correct sizing matters
Butterfly valves are often selected based on diameter and pressure class alone. The operational reality is different: disc bending, hydrodynamic loading, and bearing life define long term reliability. This article guides the main checks to ensure robust designs.
Shell & Disc Thickness
Compute shell thickness from internal pressure, diameter, and allowable stress. For discs, evaluate bending stresses due to differential pressure and hydrodynamic loads and set minimum face thickness accordingly.
Shaft & Bearing Loads
Perform combined bending and torsion checks for the shaft and calculate bearing contact pressure. Bearing selection must consider both radial load and any axial thrust generated by eccentric flow.
Torque Envelope & Actuation
Evaluate torque across key positions (0°, 10°, 30°, 90°). Include seating friction and hydrodynamic torque — present the result as a curve for actuator selection. V-Calc automates the torque-vs-angle output and recommends actuators by torque capacity and service factor.
Sealing & Gland Flange Checks
Ensure packing/seat compression through gland flange checks. Provide bolting torque and gasket stress calculations to maintain leakage class at pressure test and operating conditions.
Final Steps & Deliverables
- Excel sheet with inputs & results
- Torque curves for actuator sizing
- Materials table & bolting schedule
- Pass/Fail notes against API 609 clauses