If it is desired that a door shall swing in both directions, it should be hung with double-action spring hinges. A door pivoted top and bottom near one edge would, of course, swing both ways, but as it is considerable trouble to close a door that does not have a stop, so that it will stay at the proper place, a spring is a practical necessity on all "fly" doors, both to close them and to keep them in the proper position when not being operated. Double-action hinges are especially desirable on pantry doors opening into the dining room, and on vestibule doors in public buildings. They are sometimes used on outside doors of buildings of a semi-public character, but as a double-action door cannot be made tight, nor cannot be so well locked, it is better to use ordinary butts with an overhead door check on such doors.
There are many patterns of double-action hinges on the market, several of them being constructed on the same principle, but differing more or less in slight details and in the quality of the materials. The general principle of nearly all double-action spring butts is that of two pins, one on each side of the door, connected by a central plate which lies between the two leaves of the butt when the door is closed. This is illustrated by the two diagrams, Fig. 347, which show the position of leaves of the hinge for different positions of the door. The principal difference in the various makes of butts, aside from the quality of the materials and workmanship, lies in the arrangement of the spring or springs, which close the door and bring it to its proper place after being opened. Most of the hinges have two springs (which may be either simple or compound), one around each pin, as shown in Fig. 348, which represents an old style hinge. As the door is opened the spring about the pin on which the door swings is coiled tighter, and the reaction throws the door beyond the centre, bringing the strain on the other hinge, which reacts in the same way.
All high-class hinges of this type now have the springs concealed within hollow cylinders.
Of hinges of the type described above, the Bommer, American and Oxford are perhaps the most extensively used on good work.
The Bommer hinge is shown in Fig. 349. One flange is screwed to the jamb and the other to the edge of the door, a raised shoulder on the upper and lower edges of the flanges serving as a gauge to the carpenter in putting on the hinge and securing accuracy in fitting.
The peculiar feature of this hinge is the use in the large-sized hinges of compound spiral springs inside of the cylinders, which give a very light and elastic movement, com-
Fig. 349. - Bommer Spring. Hinge.
Fig. 350. - Section Through Cylinder of bined with great power. The construction of the washers also reduces the wear and friction to a minimum. A partial section through one of the cylinders of the larger sizes, Fig. 350, gives an idea of the construction. This is not a cheap hinge, but may be depended upon to give perfect satisfaction, and to wear almost indefinitely.
These hinges are made of wrought steel, plated, and in bronze metal or brass, and in sizes to fit any door. The bronze and brass metal hinges have a continuous steel core or skeleton running from end to end, and the entire wear is upon this steel interior, not affecting in the least the bronze or brass exterior, and thus overcoming the disadvantages of bearings of soft bronze metal or brass. Single-action hinges and special patterns for office gates and water closet doors are also made with the same kind of springs.
The American spring hinge is very much like the hinge shown in Fig. 348, except that the spring is encased in cylinders made with six knuckles, resembling the joint of a loose-pin butt. This is a very powerful hinge, suitable for very heavy doors.
The Oxford hinge somewhat resembles in its general appearance the Bommer hinge, but is a cheaper hinge and more suitable for light doors.
Fig. 351 shows the "Chicago" double-acting spring butt, which differs from those previously mentioned in that the force is derived entirely from a single strong coil, working in the thickness of the door, and which is concealed when the door is closed. This hinge is made in japanned iron and bronze metal, and is very extensively used in the Western States. It is neat in appearance and has proved quite satisfactory for doors of average size.
The Oxford and Chicago spring butts are often used with one spring butt and one "blank " to a door, the blank working in the same way as the spring butt, but having no spring. The blank is used to reduce the cost.
Fig. 351-ChicagoSpring Butt.