What are block valves and where are they placed in piping systems?

Block valves (isolation valves) are manual valves used to isolate equipment or sections of piping for maintenance, safety, or operational purposes. Common types: gate valves (full open/close, low pressure drop), ball valves (quick operation, tight shutoff), and globe valves (also for throttling). Placement rules: at equipment nozzles (inlet and outlet), at battery limits, around control valves (for bypass and maintenance), at branch connections, at process unit boundaries, and upstream of relief devices. Double block and bleed for hazardous isolation. Proper valve placement enables safe maintenance without full plant shutdown.