Put simply, these are hinges which incorporate a spring action within the pivot knuckle. They are characterised by the size of the knuckle which is usually about twice the size of a standard hinge, so as to allow the spring to be built in.
Two Way Door Hinging
Single action hinges operate in only one direction as a standard hinge. However, double action spring hinges operate in two directions, thereby allowing the door to open both ways. A typical application for a double action hinge is a restaurant kitchen door.
Single action hinges are often used in place of a door closer, for the simple purpose of closing the door. In the past few years they have started to be mass produced for the domestic fire door market and can now be found in many new apartment developments.