Cisterns ~ these are fixed containers used for storing water at
atmospheric pressure. The inflow of water is controlled by a
floatvalve which is adjusted to shut off the water supply when it
has reached the designed level within the cistern. The capacity of
the cistern depends on the draw off demand and whether the
cistern feeds both hot and cold water systems. Domestic cold
water cisterns should be placed at least 750 mm away from an
external wall or roof surface and in such a position that it can be
inspected, cleaned and maintained. A minimum clear space of
300 mm is required over the cistern for floatvalve maintenance. An
overflow or warning pipe of not less than 22 mm diameter must be
fitted to fall away to discharge in a conspicuous position. All draw
off pipes must be fitted with a gate valve positioned as near to
the cistern as possible.
Cisterns are available in a variety of sizes and materials such as
galvanised mild steel (BS 417-2), moulded plastic (BS 4213) and
reinforced plastic (BS EN 13121 and 13923). If the cistern and its
associated pipework are to be housed in a cold area such as a roof
they should be insulated against freezing.
Hot and Cold Water Installations---Cisterns