Within a comparatively few years several devices have been patented for balancing sashes by means of springs instead of weights, but the author believes that only one type known as the "sash balance" has proved a practical success. The sash balance consists of a drum on which the cord or ribbon is wound, and containing a coiled steel clock spring which sustains the weight of the sash. The common type very much resembles in outward appearance the ordinary sash pulley, and is applied in practically the same way, the ribbon or cord being attached to the sashes in the same way as when used with weights.
While the sash balance in its best form works very satisfactorily, it will probably never surplant the weight and axle pulley for ordinary windows. There are many windows, however, for which sufficient pocket room for weights cannot be obtained without spoiling the effect desired or narrowing the glass, as in the bay window, Fig. 115, or where it is undesirable to break the frame into the brick jamb, and in such cases the sash balance is almost invaluable. For hanging the glass doors of show cases also, sash balances are usually preferable to weights. Sash balances are made in both side and top patterns, but the former are recommended wherever there is room at the side of the frame for the depth of mortise required. For windows of the sizes usually found in residences, the depth of the sash balance measured from the face of the pulley stile will vary from 3 to 4 inches, and this can usually be provided by cutting a small hole in the masonry or studding back of the frame if necessary.
"Tandem" and "quad" tandem "balances are made that will operate sash weighing up to 600 pounds. The tandem balances are recommended for all sashes weighing over 30 pounds, as the strain being divided, there is less wear and liability to breakage, and less depth of pocket is required.
In remodeling old buildings having plank frames without weights, sash balances will be found a great convenience, as they can easily be inserted in the old frames.
An advantage which all spring balances possess is that they act most strongly when the sash is down, enabling one to move a binding window more readily than if it were hung with weights, while when the sash is up the springs barely suffice to hold it in position and do not offer resistance to drawing down. Sash hung with spring balances should be provided with self-locking sash lifts, otherwise the lower sash might slide up.
Of the various sash balances on the market, the Pullman and Caldwell are believed to be the most extensively used, and are undoubtedly reliable. The Pullman Sash Balance Co. makes a very extensive line of sash balances adapted to all possible uses.