How Window Pulleys Work

The Window Sash

• The framing of a window, or "sash," is derived from the French word, "chassis," which means "frame." The sash holds the window panels in place, some having one large panel and many with two panels -- an upper and lower. Grooves in the sash hold the window in place by its sides, preventing them from moving forward and backward. The same grooves function as tracts for the window's panels to move upward and downward, to open and close the window. The mechanisms for a window pulley system are hidden within the vertical sides of the sash, leaving only the front of the pulley and the emerging sash cord or chain visible on the outside of the sash.

The Pulley

• The window pulley is a moveable pulley, having a grooved wheel fixed in a metal housing that is outfitted with a chain or cord wrapped around the wheel. The pulley wheel facilitates the movement of the cord or chain along the wheel and is the most integral part of the whole system. Without it, you would feel the true weight of the window as you lift it up to open or push it down to close. The window pulley system -- also called the sash pulley system -- was first development in mid-1600s France by Thomas Kinward. Since then, window pulleys have been used throughout the Colonial, Federal, Victorian, Arts and Crafts and Modernism eras of architecture, in private houses, as well as public and commercial buildings.

Sash Counterweights

• Strung to one end of the sash cord or chain and hidden behind the window sash's side walls, sash counterweights balance the weight of the window over the pulley. Made of a heavy metal -- typically cast iron -- sash counterweights were molded into stackable shapes, weighing 3 or 5 pounds each, making it easy to mix and match them to complement the weight of the window.

Window Pulley Mechanics

• Window pulleys work with all of their components in place, balanced on both sides of the window. The window is set in its tract in the window sash, and the sash cord or chain connects to its hardware near the top sides of the moveable window panel. The sash cord or chain is fed through the pulley affixed to the window sash, and the other end of the cord or chain is connected to the sash weights. The sash weights are counterbalanced to the window -- much like the weights of a scale -- and the proper balance allows the window to go up when the weights drop and go down when the weights rise. But what prevents the window from falling back down is the sash stay. The sash stay hardware holds the window steady at its desired open position, and the sash lock locks the window from opening when it should remain closed.