Page 427 - 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 6 Hot water systems

3 installations that include a single impeller outlet pump
4 installations that use mains cold and mains-fed hot water systems
5 installations that use supplies where there is an imbalance in supply
pressures, such as those systems that use a combination boiler/instantaneous
hot water heater for the hot water supply.
We will look at each of these installations in turn.

Installation of shower mixing valves using cistern-fed KEY TERM
supplies Stratification: in a hot
water storage cylinder,
Shower mixing valves fed from a storage cistern require equal pressures on water forms in layers of
both the hot and cold supplies to maintain the correct mixing ratio of hot and temperature from the top of
cold water. The safest type of valve to use is the thermostatic type, which the cylinder, where the water
maintains a constant temperature irrespective of the temperature of the is at its hottest, to the base
incoming hot and cold supplies to the valve. Ordinary mixing valves also work where it is at its coolest.
well with cistern-fed supplies. It has to be remembered, though, that because Stratification is necessary if
ordinary mixing valves are not thermostatically controlled, the water will the cylinder is to perform to
its maximum efficiency and
eventually become cooler the longer the shower is used. This is because of manufacturers will purposely
stratification within the cylinder. design storage vessels and
cylinders with stratification
To create enough pressure to give a reasonable shower, there has to be a minimum in mind. Designers will
of 1 m from the bottom of the cistern to the showerhead at its highest position. generally design:
● a vessel that is
cylindrical in shape
The shower mixer valve must be fed from ● a vessel that is designed
cold water cistern and hot water cylinder
providing nominally equal pressure to be installed upright
rather than horizontal
● a vessel with the cold
feed entering the
Connection of cold water 1 m minimum head cylinder horizontally.
feed to the cylinder is higher
than the cold for the shower
so that the hot water runs
out first
Connection to the Hot connection for the
cylinder made at 45º shower below the Hottest water at a max. temperature
domestic hot water
connection of 65ºC is at the top of the cylinder
65ºC
60ºC

55ºC

50ºC

22 mm pipe taken as far as possible 45ºC
before reducing to 15 mm
p Figure 6.54 Gravity-fed shower installation 40ºC
Hottest water at a max. temperature
Installation of shower mixing valves using cistern-fed of 40ºC is at the bottom of the cylinder
supplies and a booster pump: the ‘power shower’ p Figure 6.55 Stratification
There are two systems that use a shower booster pump.

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