Hydraulic and pneumatic systems, including such components as heating, ventilation, air conditioning, refrigeration, hydronic and steam systems, pressure vessels, plumbing, gas piping, process piping, mechanical equipment, air and process heaters and seals, and air vacuums and filters. A license is required when the value exceeds $10,000. A mechanical contractor who performs plumbing work with a value over $10,000 must possess a master plumber license with the State Plumbing Board of Louisiana.