What Causes Toilet Bowl Overflows

I am doing a report on toilet overflows. I know if something gets stuck in the toilet bowl, the toilet will overflow. Can anyone explain the dynamics/mechanics/hydrologic of why this happens. I need a simple explanation that almost anyone can understand. The concept is not real clear to me and I have searched every where on the Internet to find the answer--with no success.

Your help would be greatly appreciated.

Thanks!!!

Take a one gallon pitcher of water and a 12 oz glass.

Start pouring until the pitcher is empty.

That's what an overflow is.

What Causes Toilet Overflows

Terry. Thanks. Your description is super. So, the outlet from the bowl to the sewer gets blocked (clogged) and water can't escape from the bowl, right? Then when water enters the bowl from the tank on a flush, your gallon to 12 oz glass scenario comes into play.

But, in my experience, whenever I experience an near overflow or overflow, the only way to prevent it or stop the water flowing is to lift up the lid from the tank and pull up on the float ball. This shuts off the water and stops the overflow. Why does this work when on the flush all of the water from the tank has already emptied into the toilet bowl? Is the new water coming into the tank enough to tip the overflow scale, so to speak,. If so, how does that water get into the bowl if the flush valve (flapper) is closed?

I've prevented many overflows using this method but don't understand how and why it works.

There is a standing overflow pipe inside the tank and a refill tube is extended to it from the fill valve. Until you lift the float ball or float assembly, water flows into the toilet bowl........

student said:

How does that water get into the bowl if the flush valve (flapper) is closed?

Click to expand...

Here is a picture of the tube that plumber1 is talking about. It continues to send water into the bowl via the overflow even when the flapper is closed (As long as the toilet is refilling).

overflow

With the older high gpf toilets, there was more water in the tank than the toilet could hold when it was plugged. With those you had to push the tank ball, or flapper, closed before it overflowed, AND stop the refill tube from adding more water into the bowl.