Valve system configured to prevent corrosion at process liquid/vapor interface

A valve system configured for controlling a flow of a corrosive process liquid, a liquid/vapor interface of the process liquid being more highly corrosive than either the process liquid or the vapor thereof when considered separately, the valve system comprising:

• a valve having an internal process liquid volume that is normally filled with the process liquid during operation of the valve;
• a purge port provided in the valve, the purge port enabling liquid communication between the internal process liquid volume and an external purge line;
• a vertical segment included in the purge line, said vertical segment being constructed from or lined with a material that is resistant to corrosion due to contact between the vertical segment and the liquid/vapor interface of the process liquid;
• an interface level sensor configured to determine a level of the liquid/vapor interface within the vertical segment;
• and
• a non-reactive gas source configured to fill a downstream segment of the purge line that is downstream of the liquid/vapor interface with a non-reactive gas having a backpressure that causes process liquid entering the purge line to enter into the vertical segment, while preventing the process liquid from flowing beyond the vertical segment.