| 1 | Define the valve’s primary function | The valve may isolate, regulate, divert, prevent reverse flow, or relieve pressure. | Required function, normal position, operating frequency, and fail-safe requirement. | Select the valve design according to the duty rather than choosing only by pipe size. | Review the process flow diagram and valve schedule. | Poor control, unsafe shutdown, or unnecessary pressure loss. |
| 2 | Match the valve to the fluid | The valve must contain and control the process medium without excessive corrosion, swelling, or contamination. | Fluid name, concentration, viscosity, solids content, pH, toxicity, and cleanliness requirements. | Check body, trim, seat, seal, and lining compatibility with the medium. | Compare material compatibility data and chemical-resistance information. | Leakage, shortened service life, product contamination, or sudden failure. |
| 3 | Calculate the required flow capacity | The valve establishes or limits the desired flow rate under defined system conditions. | Minimum, normal, and maximum flow; inlet and outlet pressure; temperature; and fluid density or specific gravity. | Use the applicable flow coefficient, such as Cv or Kv, and check the operating range. | Perform a valve-sizing calculation for liquid or gas service. | Insufficient capacity, unstable control, or excessive energy consumption. |
| 4 | Check pressure and temperature ratings | The valve forms part of the pressure boundary and must remain safe throughout the operating envelope. | Design pressure, maximum and minimum temperature, pressure class, and transient conditions. | Confirm pressure-temperature ratings for the complete valve assembly, including seals. | Review rating tables, design calculations, and pressure-test records. | Body deformation, seal failure, leakage, or pressure-boundary rupture. |
| 5 | Select the correct connection and size | The valve connects safely to the piping system while maintaining alignment and flow continuity. | Nominal pipe size, connection type, dimensional standard, face-to-face length, and installation space. | Verify flange drilling, thread details, end preparation, and flow direction. | Compare certified drawings with the piping layout and interface dimensions. | Installation delays, misalignment, gasket problems, or connection leakage. |
| 6 | Evaluate shutoff and leakage requirements | The valve prevents unwanted flow when closed and protects equipment during isolation. | Permitted leakage rate, isolation purpose, pressure differential, and safety classification. | Choose the appropriate seat design and leakage class for the application. | Review applicable seat-leakage test results, such as ISO 5208 or API 598 where relevant. | Uncontrolled flow, energy loss, emissions, or unsafe maintenance conditions. |
| 7 | Consider actuation and control needs | An actuator positions the valve and determines how quickly and reliably the system responds. | Required torque or thrust, cycle time, control signal, available utilities, and fail position. | Match manual, pneumatic, electric, or hydraulic actuation to the control strategy. | Check actuator sizing, mounting interface, travel limits, and emergency operation. | Slow response, actuator overload, loss of control, or incorrect shutdown behavior. |
| 8 | Assess cavitation, flashing, and water hammer | The valve manages pressure changes that can create noise, vibration, vapor formation, or damaging transients. | Upstream and downstream pressure, vapor pressure, fluid temperature, closing time, and line velocity. | Use suitable trim, staged pressure reduction, controlled closing, or surge protection where required. | Complete a hydraulic transient or cavitation assessment. | Noise, vibration, erosion, pipe damage, or premature valve failure. |
| 9 | Verify standards and documentation | Documentation demonstrates that the valve meets the project’s technical, safety, and regulatory requirements. | Required design, testing, material, traceability, inspection, and regional compliance documents. | Specify applicable standards, inspection points, certificates, and language requirements in the purchase order. | Check material certificates, dimensional reports, test certificates, and manuals. | Customs delays, rejected equipment, difficult approval, or unclear maintenance procedures. |
| 10 | Plan maintenance and total cost | The valve must remain serviceable over its expected operating life, not only meet the initial purchase price. | Expected cycles, spare-parts availability, inspection intervals, downtime cost, delivery time, and local service capability. | Compare purchase cost, energy loss, maintenance, replacement parts, and operational risk. | Review the maintenance manual, spare-parts list, warranty terms, and lifecycle-cost estimate. | Unexpected downtime, high operating cost, or prolonged equipment outages. |
