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| A counterbalance used to balance a lever. These are often seen on road barriers where one end of the lever is much shorter than the other end. © Eugene Brennan |
Standing at the side of the parish church this morning, collecting for the SVP, I noticed the parish centre still has sash windows. I’m not sure whether these are the original ones; I would have thought they’d have rotted away by now. So maybe some or all of them are timber replacements. As six-year-olds in Sr Brendan's senior infants or "high infants" as we called it, one of the chores that was sought after was being allowed to sweep the leaves on the lane up to the playing field, where the Millstream Court houses are now located. The other was being given the job of opening or closing the sash windows in the classroom. In our young minds, either of these tasks gave us a sense of being very important people. Opening the sash windows required a special tool: a long pole with a brass attachment on one end that hooked into a ring on the window. A quick Google search tells me these are called "sash lifts", "ring pulls" or "sash loops". Light sashes, like the ones we used to have in our houses in Nicholastown can be lifted by hand. Heavier sashes require a counterbalance.
What are counterbalances used for?
A counterbalance is a weight added to one end of a pivoted or suspended structure so that it becomes balanced (the turning moments clockwise and anti-clockwise are equalised). The weight of the counterbalance and its position relative to the pivot are set so that the structure can stay at any angle without turning. The advantage of a counterbalance is that a structure only has to be displaced and doesn't have to be physically lifted. So for instance a heavy road barrier could be raised by a human if it moves freely on its pivot, without the assistance of a motor or hydraulics. If there was no counterbalance, they would have to push down a lot harder on the barrier to lift the other end. Counterbalances are also used on tower cranes to balance the boom so that the crane doesn't topple over. These counterbalances are usually large blocks of concrete. Swing bridges use counterbalances to balance the weight of the swing section. Sometimes the counterbalancing force is provided by a spring instead of a weight. For instance springs are sometimes used on the deck of a lawn mower so a user doesn't have to lift the deck when adjusting the height. Also springs might be used on the lid of a home appliance such as a chest freezer to stop the lid falling down when raised.
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| A tower crane. The counterbalance consisting of a collection of concrete slabs can be seen on the underside of the boom. Conquip, public domain image via Pixabay.com |
Heavy sash windows, like those found in old Georgian houses, have sash weights that counterbalance the weight of the sashes. Without these weights, it would be difficult to raise and lower the sashes by hand using a pole. A sash cord is attached to each side of the sash; these cords pass up and over pulleys at the side of the window and then back down to the sash weights. The sash cords, pulleys and weights are hidden within compartments at the sides of the windows, accessible by opening hinged panels. When I was in college, I had to replace a broken sash cord on a window in a flat I was staying in (quicker than getting the landlord to do it). In those days it was easy to get such cord in a hardware store. I'm not sure whether it's still readily available. Perhaps in Dublin it is, considering the numbers of terraces of Georgian houses with sash cord that may be hundreds of years old.