Mira Realm Installation, Operation, Maintenance Manual page 11

2.4. Unvented mains pressure showers - The shower can be installed with an
unvented, stored hot water cylinder. Only a "competent person" as defined by
the Building Regulations may fit this type of system.
For packages with no cold water take off after the appliance reducing valve, it
will be necessary to fit an additional drop tight pressure reducing valve when the
mains pressure is over 3 bar. The drop tight pressure reducing valve must be
set at the same value as the unvented package pressure reducing valve.
Note! An expansion vessel MUST be fitted (and regularly maintained) if any
form of backflow prevention device is fitted, e.g. non-return valve, PRV. This
will ensure that excess expansion or pulse pressures do not damage the
product or the plumbing system.
The layout and sizing of pipework MUST be such that nominally equal inlet
supply pressures are achieved AND the effects of other draw-offs are minimized.
Safety devices
shown for clarity
Expansion
Vessel
High
Inlet
Pressure
Combined outlet PRV
with internal non-return valves
- Expansion vessel required.
not
Reduced
pressure to
COLD
shower
cold inlet
Reduced
pressure to
unvented
cylinder
HOT
High
Inlet
Pressure
Cold take-off after PRV
- Expansion pressure taken up by
unvented cylinder expansion vessel.
Reduced
pressure to
shower
cold inlet
Reduced
pressure to
unvented
cylinder
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