The Cleveland Controls DFS-221-199 Pressure Switch is an airflow proving device designed to monitor air pressure in HVAC systems. It operates using a diaphragm that responds to positive, negative, or differential air pressure, activating a snap-acting switch when a preset level is reached. This action verifies proper airflow before allowing system operation. Commonly used in furnaces, duct heaters, and ventilation systems, it enhances safety and performance. Benefits include reliable airflow detection, protection against unsafe operation, durable construction, and improved efficiency of HVAC equipment.