WC Cistern

[wotisit]

How does the flush valve operate?

[Mortartube]

Imagine a cylinder with a piston in it. The cylinder is full of water and the piston is at the bottom. The piston has holes in it. Over the top of the piston is a flexible plastic sheet. When you flush the loo, the piston lifts the column of water above it and this flushes the loo. As the piston goes back down the cylinder, the edges ot the flexible sheet lift to allow water to pass into the upper part of the cylinder. The weight of the water then holds the sheet flat over the the top of the piston (and the holes in it). The whole cycle is then ready to begin again.

http://en.wikibooks.org/wiki/Wikijunior_How_Th ings_Work/Flush_Toilet