Page 587 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 9 Sanitation systems

Flushing the urinal KEY POINT
Defra’s guidance to the Water Supply (Water Fittings) Regulations 1999 states
that urinals may be flushed with either: How an automatic
a manual or automatically operated cistern; or flushing siphon works
b a pressure flushing valve directly connected to a supply or Refer to Figure 9.59.
When the level of the
distributing pipe which is designed to flush the urinal, either directly water reaches the top
manually or automatically, provided that the flushing arrangement of the dome, the head
incorporates a backflow arrangement or device appropriate to fluid of water at point A
category 5. becomes greater than
the pressure at point B.
Clause G25.13 states: The water pressure in the
Where manually or automatically operated pressure flushing valves are trap (point C) overcomes
used for flushing urinals, the flushing valve should deliver a flush volume the air pressure inside
not exceeding 1.5 litres per bowl per position each time the device is the siphon and this
initiates siphonic action,
operated. emptying the cistern.
There are two ways that urinals can be flushed:

1 by the use of an automatic flushing cistern
2 by the use of a flushing valve.
A
The automatic flushing cistern
As the name suggests, automatic flushing cisterns use an automatic B C
flushing siphon to flush the urinals automatically when the water reaches a
predetermined level in the cistern. The Water Regulations state that any auto-
flushing cistern must not exceed the following water volumes: p Figure 9.59 Automatic
flushing siphon
● 10 litres per hour for a single bowl or stall
● 7.5 litres per hour per urinal position for a cistern serving two or more urinal
bowls or 700 mm of slab.
The maximum flow rate from any automatic flushing cistern must be regulated
by the inflow of water from the cold supply. This can be done quite easily by
the use of urinal flush control valves such as a hydraulic flush control valve
fitted to the incoming water supply. The hydraulic flush control valve allows
a certain amount of water through to the cistern when other appliances like
taps and WCs are used, rather than have a constant supply of water dripping
into the cistern. The sudden reduction in pressure on the mains supply opens
the hydraulic flushing valve to allow a certain amount of water through. The
amount of water can be varied depending on the installation requirements and
number of urinals. The idea here is to prevent the urinals flushing when the
building is not being used, thus saving on wasted water.

The flushing valve
This is a new method of flushing a urinal that involves the use of either a
manual or automatic valve, which delivers a short 1.5-litre flush to an individual

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