Balance: A mechanical device, normally spring-loaded, used in hung windows to counterbalance the weight of the sash during operation.
History of Spring Balance Systems
The Old House Journal shares some intriguing history on the invention and original uses of a spring balance system to replace to weight and pulley system. Here’s an excerpt:
The Source of Springs
In the 1890s, as the Industrial Revolution was reaching its peak, technological achievement became both the essence of the American spirit and good business. Everyone wanted to patent a better mousetrap, and there was a steady stream of novel inventions seeking to improve every industry, including building construction. The need to conveniently control double-hung sash had spawned many gizmos, from cams and ratchets to tension bars and spring pins, but the spring balance, which first appeared in the 1880s, was something different.
Also called a tape or clockspring balance, the spring balance is a metal tape, permanently greased and wound on a wheel. This wheel in turn is mounted on a coiled, high-carbon steel spring inside a metal case, similar in construction to a small carpenter’s measuring tape. Just as cast iron or lead weights were matched, pound for pound, to each sash, spring balances were manufactured and sold in various sizes that would offset the weight of a particular sash. However, instead of running cotton rope from sash to weights over a pulley, the spring balance connected to the sash by a metal tape that stretched up the channel into the spring case that took the place of a pulley. Visually, there was little difference.
At the turn of the 20th century, Frank Kidder’s pioneering guide Building Construction (1913) listed several reasons for choosing spring counterbalances. The primary advantage was that the spring balance required less space than weight-and-pulley systems, which had to leave several inches of room for weight pockets on either side of the window. This was especially important on bay windows (or the increasingly popular banks of windows) where the mullion space between sashes was limited. Spring balances were also invaluable for plank-frame houses, where the absence of wall framing made weight pockets impossible, and in solid brick walls, where spring balances alleviated the need to build openings any wider than necessary for the window proper. By 1894, the Sensible Sash Balance of Groton, New York, was one of several spring balances being advertised. A decade later Kidder mentioned two sources for spring balances: Pullman Manufacturing Company and Caldwell Manufacturing Company, both of Rochester, New York. Though Caldwell balances are no longer sold, Pullman spring balances have been on the market since 1886 and are still manufactured today.
Marvin double hung windows, inserts and tilt pacs use modern spring balances that allow you to leave the original weights and weight pockets in place when replacing an old window.