33 ©ESP Ltd. Sept 2008
All Reliance Inlet Control Groups are supplied with comprehensive Installation
and Maintenance instructions to supplement the relevant Unvented System
manufacturer‟s Instructions.
The final “functional control” - a means to accommodate the expanded water to
prevent waste of water - is also supplied with the Unvented System. This is
achieved in two ways - either by using an external Expansion Vessel or an inter-
nal air bubble generated within the unit.
External Expansion Vessel
Supplied in various sizes, dependent on the water capacity of the Unvented Sys-
tem, the Expansion Vessel has an inner butyl rubber membrane which is sur-
rounded by a cushion of air, the pressure of this air cushion corresponding to the
set pressure of the relevant manufacturer‟s Pressure Reducing Valve. When the
water is heated, the additional volume flows into the bag-type membrane, com-
pressing the air cushion and accommodating the expanded water. On cooling
down, the volume of water decreases, thereby “deflating” the inner membrane.
The Expansion Vessel must be sited
either directly on the Unvented unit
or, as in most Unvented Systems util-
ising this method to accommodate the
expanded water, the Inlet Control
Group.
The RWC range of Expansion Vessels
used on domestic Unvented Systems
are supplied in a white finish to com-
pliment the “white goods” image of
the Unvented unit.
All potable Expansion Vessels with a nominal capacity of 16 litres or greater
incorporate a replaceable membrane to facilitate replacement in the unlikely
event of failure.
Internal Air Bubble
In this type of Unvented System, the expanded water is accommodated by
compressing the internal air bubble generated when the unit is commissioned.
Again, on cooling down, the volume of water contained within the unit de-
creases and the internal air bubble returns to it‟s nominal capacity.
This type of Unvented System is commonly known as a Bubble-Top unit.
Safety Controls
Required to protect the householder and prevent the temperature of the water
in the Unvented System exceeding 99°C, these controls provide a three tier
level of protection.
•
Control thermostat - usually set between 60-65°C.
•
Energy cut out device with manual reset - usually set between 85-89°C.
Temperature & Pressure Relief Valve - set to 90°C + 5°C.
Both the Control Thermostat and Energy cut out device are supplied by the
manufacturer, the Control Thermostat offering the first level of protection
against over temperature of the water. The Energy cut out device will offer
the second level of protection in the event of Control Thermostat failure. The
Energy cut out device must incorporate a manual reset feature and must not
be self-resetting.
UNVENTED HOT WATER STORAGE SYSTEMS AND CONTROLS
