Which multi-turn valve is used for corrosive wastewaters?

• A. Gate valve
• B. Globe valve
• C. Pinch valve
• D. Diaphragm valve

Answer: (D)

For corrosive wastewaters, you want a valve that keeps the liquid away from most of the metal parts and can use chemically resistant materials. A diaphragm valve does this by using a flexible diaphragm as the sealing element, with the fluid contacting the diaphragm rather than the valve’s metal components. The diaphragm and seats can be made from highly resistant materials such as PTFE or other polymers, so acids or caustics don’t attack the critical parts. This design minimizes corrosion of the valve internals, reduces leakage risk, and handles the often dirty, harsh wastewater typical of corrosive services.

Gate and globe valves involve metal-to-fluid contact over the sealing surfaces, which can corrode more quickly in corrosive waste. Pinch valves rely on a rubber or elastomer sleeve, which can degrade or be damaged by corrosive chemicals, making them less reliable for this service.