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69
ter, insects and light as well as being thermally insulated and not contaminating
the stored water themselves. Tanks are generally not larger than 2 m long by
1 m wide by 1 m high, and pipe connections must ensure that water flushes
through all of them to eliminate stagnation.
Servicing or isolating valves are located on the inlet to all ball valves on
storage tanks and WC cisterns to facilitate maintenance without unnecessary
water loss or inconvenience to the occupier. A servicing valve is required on all
outlets from tanks of more than 151, that is, larger than a WC cistern.
The drinking and food-rinsing water tap at a kitchen sink must be con-
nected to the water main before any water softener enters and a check valve is
required between this tap and the softener.
Service entry into a building is via an underground pipe passing through a
drain pipe sleeve through the foundations and rising in a location away from
possible frost damage. An external stop tap near the boundary of the property is
accessible from a brick or concrete pit. A ground cover of 760 mm is main-
tained over the pipe. A stop valve and drain tap are fitted to the main on entry to
the building to enable the system to be emptied if the building is to be unoccu-
pied during cold weather.
A water meter is the next pipe fitting. This has a rotary flow sensor which
is used to integrate the quantity of water that has passed. The cubic metres of
water that are supplied, and charged for, are assumed to be discharged into the
sewer. A separate charge is levied for the supply of potable water and for the
acceptance of the contaminated discharge foul water. The consumer normally
has no choice but to pay both the charges.
In tall buildings the pressure required to reach the upper floors can be
greater than the available head, or pressure, in the mains. A pneumatic water-
pressure-boosting system is used. Float switches in the storage tanks operate the
pump to refill the system and minimize running times to reduce power con-
sumption. A delayed-action ball valve on the cold-water storage tanks can be
used. This delays the opening of the ball valve until the stored water has fallen
to its low-level limit. System pressure is maintained by a small air compressor
and pneumatic cylinder.
The controller relieves excess pressure and switches on the compressor
when the air pressure falls. During much of the day, water is lifted pneumati-
cally at much lower cost than if it were pumped.
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