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The Basic
The system at natural atmospheric pressure as the
feed/expansion tank is open to the air. The feed/expansion tank fitted
high up above the rest of the system, often in the loft. The tank is
fitted with a ball valve so that any water lost due to evaporation etc is
automatically replaced, the tank also allows for the water in the system
to expand when it is heated, the ball valve need to be set very low so
that expanded water does not cause on overflow. The tank also allows for
any water vented from the system up the vent pipe to be recovered, the
vent pipe is connected from near the boiler and is bent over the tank.
From the tank, the water is fed down to connected into the system near
the boiler.
Sealed system
A scales system
normally operates at a pressure of about 1 bar above atmospheric
pressure, this pressure is achieved by filling loop connected from the
mains water supply to the system. A stop cock in the link allows for the
system pressurized as required. Once pressurized, the system should
retain its pressure unless radiators are bleed or there is leak in the
system. To avoid potential damage by excess pressure within the system
(which normally occur if there is fault in the system) ,a safety relief
valve is incorporated so that any excess pressure is vented to
atmosphere. It is not generally practical to use an additive in sealed
systems as there is no way for it to be added. In hard water areas
various devices may be fitted in the feed to the filling loop to soften
the water as it is added to pressurized circuit. Such a softening device
should reduce lime scale build-up in the system. A lot of boilers are
designed specially for scaled system and incorporate the boiler controls,
expansion vessel, pressure gauge & relief valve all within one casting.
However all the various parts are available separately and it may be
necessary to use.
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