Page 576 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

ACTIVITY 6 litres for a long flush and 4 litres for a short flush. The water can be delivered
to the WC pan in several different ways, depending on the cistern design:
Refresh your knowledge of ● By the use of a siphon: the traditional way to flush a WC cistern. The
service valves and float- cistern is flushed using siphonic action (see Chapter 3, Scientific principles,
operated valves; these page 176). The WC flushing handle is connected to the siphon by a link pin.
were covered in detail in
Chapter 5, Cold water When the WC cistern handle is depressed, the link pin lifts a plunger in the
systems. siphon bell, which has a large thin plastic or thin rubber diaphragm at the
end of it. The diaphragm lifts a column of water up and over the top of the
siphon to begin the siphonic action.
There are many different styles and sizes of WC siphon available and the
correct one must be chosen depending on the cistern size. Some siphons
allow different flushing volumes to be set by adjusting the height at which air
is let into the siphon bell to stop the siphonic action.

When the handle is depressed, a column
of water is lifted up and over the siphon,
which starts the siphonic process,
emptying the cistern until the water
reaches the bottom of the siphon. As air
enters the siphon, the process stops.
p Figure 9.23 How a WC siphon works
p Figure 9.24 A WC siphon

● By the use of a dual flush valve: these can be operated by pressing a button
on the top of the WC cistern, or remotely by air, which is blown through a tube
when the button is depressed. They work by simply opening up a valve when
the button is activated and this allows water to flow by gravity to the cistern.
Siphonic action is not needed. Flush valves have a 6-litre and 4-litre flush action.
Flush valves have an integrated overflow that allows water to flow straight to
the WC pan should the float-operated valve begin to overflow, so a separate
overflow pipe is not required.
● By the use of a drop valve (or flap valve): a very simple valve that allows water
to flow by gravity to the cistern. In the closed position, it is the weight of the
water that makes a watertight seal. When the WC handle is depressed, a link pin
simply lifts the valve up. These are not dual flow and will flush only as long as
p Figure 9.25 A dual flush valve the handle is pressed down. Most flap valves have an integral overflow.

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