Instead of counterweights and cords, modern sash windows use spiral balances which are mounted on the faces of the frame stiles, eliminating the need for traditional box frames. Pairs of balances are made to match the size and weight of individual glazed sashes and can be ordered through builders’ merchants or by post from the manufacturers.
Each balance consists of a torsion spring and a spiral rod housed in a tube. The top end is fixed to the frame stile and the inner spiral to the bottom of the sash. The complete unit can be housed in a groove in the sash stile or in the window frame.
You can fit spiral sash balances to replace the weights in a traditionally constructed sash window.
Remove the sashes and weigh them on your bathroom scales. Place your order, giving the weight of each sash together with its height and width, plus the height of the window frame. Refit the sashes temporarily until the balances arrive, then take them out again and remove the pulleys.
Plug the holes and paint the box- frame stiles. Cut grooves, as specified by the manufacturers, in the stiles of each sash to take the balances (1). Also cut a housing at each end of their bottom edges to receive the spiral-rod fixing plates. Fit the fixing plates with screws (2).
Sit the top sash in place, resting it on the sill, and fit the parting bead. Take the top pair of balances, which are shorter than those for the bottom sash, and locate each in its groove (3). Fix the top ends of the balance tubes to the frame stiles with the screw nails provided (4) and set the ends tight against the head.
Lift the sash to its full height and prop it with a length of wood. Hook the wire ‘key’ provided by the makers into the hole in the end of each spiral rod and pull each one down about 150mm (6in). Keeping the tension on the spring, add three to five turns anti-clockwise (5). Locate the end of each rod in its fixing plate and test the balance of the sash. If it drops, add another turn on the springs until it is perfectly balanced. Take care not to overwind the balances.
Fit the bottom sash in the same way, refitting the staff bead to hold it in place. Fit the stops that limit the full travel of the sashes in their respective tracks.
In time the springs of spiral balances may weaken. Re-tension them by unhooking the spiral rods from their fixing plates, then turn the rods anticlockwise once or twice.
The mechanisms can be serviced by releasing the tension and unwinding the rods from the tubes. Wipe them clean and apply a little thin oil, then rewind the rods back into the tubes and tension them.