Push button, flap flush, lavatory cisterns
Push button flap flush cisterns must not to be confused with the syphon type of flap valve used in other cisterns, this flap flush valve is opened and closed by a button to control the release of the water from the cistern.
As with 'normal' cisterns, the discharge, down pipe from the cistern to the lavatory pan is attached to the outlet on the bottom of the cistern below the flap valve. The moving part of the valve simply sits in the outlet from the cistern and is held in place by water above it.
Some flap flush assemblies incorporate a vertical overflow pipe which discharges any excess water into the pan - (the top illustration shows a flap valve with an integral overflow, the illustration below shows a basic flap flush valve with a separate overflow fitted to the side of the cistern).
Often a button (normally fitted to the top of the cistern cover) is used to lift the valve by means of a chain to release the water from the cistern. With the flap opened, the water just flows down the pipe to clear the lavatory pan.
By releasing the button, the flap drops back onto its seat and the water, as it fills the cistern, seals the flap against its seat.
Some flap flush valves are operated by a handle on the cistern (as a conventional syphon flush mechanism).
One 'disadvantage' of the flap flush system (compared to a syphon style flush) is that water will continually flow down into the pan when the seal on the flap becomes worn, - this does not happen when any parts of the syphon type become worn, it just becomes harder to achieve the flush action.