How does a toilet work?

Ever wonder about water closets? Here are the facts about flushing...

Modern flush toilets work in two main stages. First, in order to empty waste from the bowl, a complex flush mechanism is activated. This section is contained within the toilet’s tank – the part of the toilet positioned above the bowl – and is initiated when a user presses the toilet’s handle. Once pushed, the handle pulls up a chain connected to a flush valve – a rubber stopper that acts as a gateway to the bowl, siphon and trapway. The water in the tank, which has been filled via a filler tube from the mains supply, then exits the tank and descends into the bowl. It follows a rim shelf perforated with equidistant holes, as well as a smaller secondary passage directly into the toilet’s siphon – the kinked pipe that sits between the trapway and the bowl.

The release of the tank’s water occurs in roughly three seconds, which creates a vacuum effect that depressurises the trapway, generating a large suction force that drags the contents of the bowl down into the sewerage system.

Once flushed, the toilet’s tank needs to refill itself for further use. First, now the tank is devoid of water, the flush valve falls back down onto the gateway to the bowl. This reseals the tank. Next, the tank filler valve is switched on either electronically or by a traditional ball cock (a float mechanism that pivots on an axle to open the filler valve when the water falls). This allows water to re-enter the tank through the filler tube, filling it to a preset level, as well as down the overflow tube to refill the bowl. The filler valve is then shut once more, either by the rising of the float or by another control system. Finally, the refilling of the tank re-pressurises the siphon and trapway, blocking any gasses and waste from re-entering the system. It re-creates a large water surface area in the main bowl, ready for reuse.

Toilet technology explained

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This article was originally published in How It Works issue 24, written by Jon Jones 

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