What capability must valves used with NH3 possess?

Valves used with NH3, or ammonia, must possess backseating capability for safety and operational integrity. Backseating refers to a design feature that allows the valve stem to be replaced or re-packed while the valve is in the open position, which is crucial for preventing leaks. This capability ensures that maintenance can be performed without shutting off the flow of ammonia, thereby reducing the risk of incidents or exposure to hazardous materials.

In high-pressure systems, such as those handling ammonia, it is vital to have a robust mechanism that not only allows for ease of maintenance but also ensures that the system remains secure during such procedures. This is particularly important given the properties of ammonia, which is a toxic and corrosive substance.

While other features such as automatic shut-off, remote operation, and pressure relief are valuable in various systems, they do not address the specific requirement of maintaining secure and safe operational procedures when handling NH3. Therefore, backseating is the essential capability that valves must possess in this context.