Mira Realm Installation, Operation, Maintenance Manual page 10

2.3. Mains pressurised instantaneous hot water shower, heated from a
thermal store - Packages of this type, fitted with a tempering valve can be used
with the Mira Realm. A drop tight pressure reducing valve MUST be fitted
if the supply pressures exceed 3 bar maintained.
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 expansion vessel may already be fitted externally or
internally within the thermal store (check with thermal store manufacturer).
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.
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