Mira EXCEL Installation & User Manual page 11

Unvented mains pressure supplies
The BSM can be installed with an unvented, stored hot water cylinder. Only a
"competent person" as defined by Part G of Schedule 1 of 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, PRV. 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 BSM
Reduced pressure
to unvented cylinder
HOT
High Inlet Pressure
Cold takeoff after PRV
- Expansion pressure taken up by
unvented cylinder expansion vessel.
11
Reduced pressure to
cold inlet of BSM
Reduced pressure to
unvented cylinder