73
10.2.1 General
Dry
pipe
installations
are
normally
charged
with
air
or
inert
gas
under
pressure
downstream
of
the
dry
alarm
valve
and
water
under
pressure
upstream
of
the
dry
alarm
valve.
A
permanent
air/inert
gas
supply
to
maintain
the
pressure
in
the
pipe
network
shall
be
installed.
The
installation
shall
be
pressurised
to
within
the
pressure
range
recommended
by
the
alarm
valve
manufacturer.
Dry
pipe
installations
shall
only
be
installed
where
there
is
a
possibility
of
frost
damage
or
the
temperature
exceeds
95°C,
e.g.
in
drying
ovens.
10.2.2 Sprinkler orientation
All
sprinklers
in
a
dry
pipe
installation
shall
be
fitted
in
the
upright
position,
except
where
dry
pendent
pattern
or
sidewall
sprinklers
are
used.
10.2.3 Size of installations
The
net
volume
of
the
pipework
downstream
of
the
control
valve
set
shall
not
exceed
that
shown
in
Table
20.
NOTE:
it
is
strongly
recommended
that
dry
and
alternate
installations
should
not
be
used
for
HHS
applications,
since
the
delay
in
water
reaching
the
first
operating
sprinklers
could
seriously
impair
the
effectiveness
of
the
system.
T
Table 20: Maximum size per installation - Dry and alternate installations
Maximum
volume
of
pipe
work
(m
3
)
Without
accelerator
or
exhauster
With
accelerator
or
exhauster
4,0
10.3 Alternative installations
10.3.1 General
Alternate
installations
incorporate
either
an
alternate
alarm
valve
or
composite
set
comprising
a
wet
alarm valve
and
a
dry
alarm
valve.
During
the
winter
months
the
system
piping
downstream
of
the
alternate
or
dry alarm
valve
is
charged
with
air
or
inert
gas
under
pressure
and
the
remainder
of
the
installation
upstream
of
the
alarm
valve
with
water
under
pressure.
At
other
times
of
the
year
the
installation
operates
as
a
wet
pipe installation.
10.3.2 Sprinkler orientation
All
sprinklers
in
an
alternate
installation
shall
be
fitted
in
the
upright
position,
except
where
dry
pendent
pattern
or
sidewall
sprinklers
are
used.
10.3.3 Size of installations
The
net
volume
of
the
pipework
downstream
of
the
control
valve
set
shall
not
exceed
that
shown
in
Table
20.
10.4 Pre-action installations
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