Mira Gem 88 Installation & User Manual page 13

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 5 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 or check valve. This
will ensure that excess expansion or pulse pressures do not damage the product
or the plumbing system.
Safety devices
not shown
for clarity
Expansion Vessel
High Inlet Pressure
Combined outlet PRV
with internal non-return valves
- Expansion vessel required.
COLD
Reduced pressure to cold inlet of shower
Reduced pressure
to unvented cylinder
Unvented Mains Pressure Showers
HOT
High Inlet Pressure
Cold takeoff after PRV
- Expansion pressure taken up by
unvented cylinder expansion vessel.
13
Reduced pressure to
cold inlet of shower
Reduced pressure
to unvented cylinder