CHECK VALVES ARE DESIGNED FOR USE IN COMPRESSED AIR SYSTEMS TO CONTROL THE FLOW OF AIR FROM THE COMPRESSOR INTO  A RECEIVER,  WHEN THE COMPRESSOR REACHES UNLOAD PRESSURE, THE CHECK VALVE CLOSES, PREVENTING THE BACKFLOW OF AIR FROM THE RECEIVER INTO THE DISCHARGE LINE. GDB INC IN-TANK CHECK VALVES SCREW DIRECTLY INTO THE RECEIVER AND ARE ATTACHED TO THE COMPRESSOR'S DISCHARGE LINE AT THEIR INLET. VARIUS SIZES AND CONFIGURATIONS ARE AVAILABLE. GDB INC IN-LINE CHECK VALVES SCREW DIRECTLY INTO THE DISCHARGE LINE AND HAVE THE SAME SIZE INLET AS THEY DO OUTLET. GDB INC CAST BRONZE CHECK VALVES ARE SIMILAR TO IN-LINE CHECK VALVES BUT OFFER HIGHER FLOW CAPABILITIES. VARIOUS SIZES AND CONFIGURATIONS ARE AVAILABLE.