- #1
fourthindiana
- 162
- 25
I read David Macaulay's description of how a toilet flushes in Macaulay's book The New Way Things Work, and I don't fully understand it. Macaulay says that air pressure in the tank of water for a toilet exerts a force that pushes down on the water in a tank of a toilet. I suppose the air pressure that exerts a force pushing downward on the water in the tank of a toilet is just the atmospheric pressure. I understand everything so far. But then I read Macaulay's numbered descriptions of how a toilet flushes, and I no longer fully understand it. Macaulay's description of how a toilet flushes is divided into three stages. I understand the third stage, so I won't describe the third stage. The following is a quote of Macaulay's description of the first two stages of a toilet flushing:
"1. The Tank Flushes
After the handle is pressed down, water is lifted up the siphon tube by the disk. The water reaches the bend in the siphon pipe and then travels around it. As it falls, the water in the tank follows it.
2. The Valve Opens
When the water level in the tank falls below the bottom of the bell, air enters the bell and the siphon is broken. By this time, the float has fallen far enough to open the valve, and water under pressure enters to refill the tank and the float begins to rise again."
Below are photographs I took of the pictures in Macaulay's book.
Since the air pressure exerts a force that pushes downward on the water in the tank at all times, and since the force that air pressure exerts on the water is sufficient to push all the water up the siphon tube and past the bend until the water level falls below the bottom of the bell, I don't see why the air pressure would not force the water up the siphon tube on its own without the disk lifting water up the siphon tube. Why won't the air pressure exerting a downward force move all the water in the tank up over the bend in the siphon tube until the water level falls below the bell without the disk pushing the water up the siphon tube?
"1. The Tank Flushes
After the handle is pressed down, water is lifted up the siphon tube by the disk. The water reaches the bend in the siphon pipe and then travels around it. As it falls, the water in the tank follows it.
2. The Valve Opens
When the water level in the tank falls below the bottom of the bell, air enters the bell and the siphon is broken. By this time, the float has fallen far enough to open the valve, and water under pressure enters to refill the tank and the float begins to rise again."
Below are photographs I took of the pictures in Macaulay's book.