Page 300 - 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

Break cisterns are often used in very tall buildings as intermediate cisterns on
nominated service floors, thus dividing the system into a number of manageable
pressure zones. The break cisterns provide water to both user outlets and other
break cisterns higher up, where the water is then boosted to other pressure
zones further up the building.
As with all cistern installations, break cisterns must be fitted with an
appropriate air gap that ensures zero backflow into any part of the system.
Type AB air gap × 2 the inlet pipe diameter Head over weir Not less than 25 mm
Not less than 25 mm
Incoming mains Screened overflow pipe
cold water supply S
Screened warning
pipe
Solenoid valve shown
but this could be a float-
operated valve, equilibrium
float valve or delayed-action
float valve
Float switch
Weir overflow to be sized in closing the
accordance with the diameter solenoid
of the incoming water supply
valve

Float switch to shut down the
boosting pumps so they do not Float switch opening Cold supply to the
run dry in the event of lack of water the solenoid valve boosting pumps
p Figure 5.54 The layout of a break cistern with a raised chamber

Frost protection of pipes, fittings and cisterns

You can never fully protect against freezing temperatures. No matter how much
insulation we wrap around pipes and fittings, if the weather gets cold enough
the pipes will freeze. Therefore, we merely delay the freezing process as long as
we possibly can by insulating.

When we insulate pipes, we are not attempting to ‘keep the cold out’. The idea
of insulation is to keep in the heat that is already there. In other words, we are
attempting to retain the ‘heat energy’ already present in the water for as long as
possible. This means insulation is important even under normal conditions as it
maximises energy efficiency. The greater the thickness of insulation, the longer the
heat energy is retained. This is illustrated in Figure 5.55, where you will see that,
p Figure 5.55 Insulation around for a greater volume of water, i.e. larger pipe sizes, less insulation will be needed.
pipes
The Defra guidance to the Water Supply (Water Fittings) Regulations 1999
(G4.2) states:
All cold water fittings located within a building but outside the thermal
KEY POINT envelope, or those outside the building must be protected against damage

The thermal envelope is by freezing.
defined as that part of a
building that is enclosed The Defra guidance to the Water Supply (Water Fittings) Regulations 1999
within walls, floor and (G4.3) states:
roof, which is thermally If the frost protection provided is insufficient for exceptional freezing
insulated in accordance conditions or the premises are left unoccupied without adequate heating,
with the requirements of damage and leakage can often be avoided by shutting off the water supply
the Building Regulations.
and draining down the system before the onset of freezing.

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