Page 429 - 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

Care must be exercised when making the hot connection to the cylinder. There
are two ways in which this can be done. The first method involves installing
the hot water draw-off from the cylinder at an angle of between 30° and 60°,
with the hot shower pump connection being made at an angle of 90° with a tee
piece (see Figure 6.56). This allows any air in the system to filter up to the vent
and away from the hot shower pump inlet.

The second method involves making a direct connection to the cylinder using
a special fitting called an Essex flange (see page 389). With this method, the
hot water is taken directly from the hot water storage vessel, avoiding any air
problems that may occur.

Systems that use a single impeller pump off the outlet from the
mixer valve
These boost the water after it has left the mixer valve. They are usually used
with concealed shower valves and fixed ‘deluge’-type, large water volume
showerheads.

In both of these installations, the pump increases the pressure of the water,
which means that the minimum 1 m head is not necessary. However, a
minimum head of 150 mm is required to lift the flow switches as these switch
the pump on. With some installations it is possible to install the pump with a
negative head, where the cistern is lower than the pump, provided that a means
of starting the pump is in place, such as a pull-cord switch.

Installation of shower mixing valves from mains hot
and cold supplies

The installation of unvented hot water storage cylinders is covered earlier in
this chapter. You may be required to install or maintain shower mixing valves
that are installed on this type of system.

With this type of installation, shower pumps are not required as the hot and
cold supplies are fed direct from the mains cold water supply via a pressure
reducing valve that reduces the pressure of the water to the operating pressure
of the unvented hot water storage cylinder. The obvious advantages of this are:
● the amount of water that can be delivered to the showerhead
● the force of the water leaving the showerhead, giving a powerful
‘continental’-type shower.
Because the unvented hot water cylinder usually operates at a slightly lower
pressure than the mains cold water supply, the cold water to the shower must
be at the same pressure as the hot water supply. This means that the cold supply
needs to be connected after the pressure reducing valve but before the single
check valve on the unit (see Figure 6.58) to ensure equal hot and cold pressures.

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