Valves can represent as much as 30% of the cost of process-fluid transfer systems in a process plant. Together, valves and piping can make up the largest singles investment in a process plant, constituting about 23% of the total capital expenditure for equipment and materials. Process vessels, at about 15%, represent the next most expensive plant component. Lagging behind in this respect are such other major equipment items as pumps (about 4%), compressors (also about 4%), drives (about 7%) and furnaces (again, about 4%)