Put spring into coupler and screw in other hose barb. Make sure the thumb tack's rounded edge is facing the o-ring. This will create a seal when air tries to return to the source. You will have to experiment with the spring and torque of the hose barbs depending on the amount of air you are using. Stretch or compress the spring if needed. I tested mine up to 150 psi with no backflow. This is for inline application, but replace one barb with a nipple if you want to direct-thread it to a tank or other application.