Selection of chemical resistant valve
The selection of a chemically resistant valve requires a proper matching of the valve construction to chemical media and operating conditions.
1.What is the chemical media ? State the chemical name, concentration, purity and any additives. Even the same chemical in different concentrations, can behave differently for materials. Is the media corrosive, oxidizing, abrasive or crystallizable ?
2.Check chemical resistance of materials. Analyze the valve body, seals, gaskets, seat and other wetted parts. The limits of chemical resistance are different for stainless steel, PVC, PP, PVDF, PTFE, EPDM and FKM. Don’t assume material is corrosion resistant simply because it is marketed that way. Check compatibility with the manufacturer.
3.Define operating conditions. Determine the minimum, normal and maximum pressure and temperature. Look for pressure surges, vacuum conditions and temperature fluctuations that can negatively impact the valve integrity or sealing.
4.Establish flow requirements. Establish the required flow rate and allowed pressure drop. Compare the flow coefficient, port size and flow characteristics of the valve.
5.Select valve type. Depending on the application select ball, diaphragm, needle, solenoid or other valve types. Determine whether you need just isolation, on/off switching or flow regulation.
6.Select the actuation method. Manual, electric, pneumatic and solenoid actuation have different installation and control requirements. Automated valves also have to comply with the available power supply and control signals.
7.Check connection compatibility. Specify pipe size, thread type, flange type, installation position and available space.
8.Evaluate maintenance and safety aspects. Think about the implications of leaks, chemical containment, cleaning requirements, inspection access and availability of spare parts. Some processes may be dangerous and require special materials or certified equipment.
9.Review quality documentation. Ask for technical drawings, material specifications, pressure and temperature ratings, chemical compatibility data and test reports if appropriate.
Finally, estimate the total cost of ownership, not only the cost of purchase. Right valve selection will help to reduce maintenance, downtime and premature replacement of the valve while ensuring reliable control of industrial chemicals.
Tips to Avoid Common Mistakes in Design of Chemical process valve
Don’t assume chemical resistance to all chemicals. Check the exact chemical composition, concentration, temperature and time of exposure.
Don’t choose just names of materials. Check all wetted parts (body, seals, seat, gaskets).
Don’t undersize or oversize the valve. Determine the required flow rate and pressure loss.
Test the full range of pressure. Take into account startup, shutdown, pressure surges and vacuum conditions if applicable.
Consider temperature variations. Increased temperature can change seals’ properties and accelerate chemical attack.
Select the right valve type. See if the application requires isolation, switching, throttling or precise control.
Consider fluid contamination. Particles and crystallizing chemicals can obstruct valve internals and damage seals.
State the right connections. Installation problems and leaks can occur due to improper thread or flange standards.
Provide safe service. Valves isolation points, drainage arrangement and access for inspection.
Consider appropriate standards. Verify certifications if applicable (pressure, electrical, environmental, etc.)
