Brass air compressor non-return (check) valves.
Material and Durability: These valves are typically made from copper or brass material, which makes them corrosion-resistant, pressure-resistant, and durable for long-term use in air compressor applications.
Function: As non-return valves, they ensure that compressed air flows in only one direction, preventing backflow from the air tank to the compressor pump once the system is shut off or during operation.
Design: The specific valves in the image appear to be 3-port models, designed with different male thread sizes (e.g., 1/2" x 1/2" x 1/8") to connect the pressure vessel, pump, and an unloader or relief line.
Reliability: They are known for their high reliability and compressive strength, providing a safe and effective mechanical device for pneumatic systems.