Valve vs. Siphon
WC valve-flushing devices have been known to leak for 160 years. The siphon can never leak.
In the UK, all toilets with flush handles have a siphon in the cistern. All toilets with push-buttons have either a drop-valve or a flap-valve in the cistern, both of which are liable to leak (approximately 35 litres per person per day -US EPA 2010 estimate).
A siphon must have a flush handle in order to give the leverage or mechanical advantage needed to lift the water in the chamber up and over the siphon to start the flush or siphonic action. You simply cannot exert enough force via a push-button to lift the chamber water.
The reason why siphons never leak is because the only time that water can get from the water-filled up leg to the air-filled down leg, is when it is pushed there by pressing the flush handle. If the diaphragm fails – the bit that lifts the water – the toilet will simply not flush but it will categorically not leak.
With valve-flushing devices, there is no lifting of water so there is no need for a flush handle. The valve seal is at the bottom of the cistern. Simply raise the valve seal and water flows into the pan by gravity. Very little force is needed to lift the valve seal so it can be done with a push-button.
The reason why valve flushing devices are so prone to leak is because there is always water above the valve seal, like a plug in a sink. When the seal fails, as it invariably will, water will leak continuously into the pan until it is repaired or replaced – an industry in itself.
Valve manufacturers do not deny the fact that their devices leak. When asked the question, ‘don’t these valve flushing devices leak?, an executive of one of the largest valve manufacturers in America, replied, ‘of course they leak, that’s why we sell so many’. This is ok for them but results in excessive water bills and water waste.
The water wastage from leaking valve devices in the mid 1800s led to the introduction of the siphon. Invented by Thomas Crapper and others as a water saving measure, the siphon was originally called the ‘water waste preventer’. This development led to valve flushing devices being outlawed in Britain in 1861; the siphon was then the only flushing device authorised to be used in a British cistern.
Unfortunately in 1999, valve-flushing was again made legal for the purpose of European harmonisation. Coming in under the banner of ‘water efficiency’, it was marketed on the basis of 6-litre flushing and dual-flush capability – with the added lure of simple push-button operation.
If valve-flushing completely replaces siphon-flushing in the UK we will have to find 12% more water for the expected leakage, the repercussions of which would cost consumers around £2 billion per year.