<Appendix A. Air Supply System>
A-2
IM 21B03D01-01E
(2) Example for Field-Mounting Instruments
Figure A.2 shows an air-supply system for service
point with respect to field-mounting instruments
(individually installed instruments).
Securely install a filter and reducing valve in air
supply piping that is nearest to an instrument.
(These devices are not required if the instrument
has a filter and reducing valve.)
Also, it is recommended that a shut-off valve be
installed in the air supply pipe to allow removal of
individual instruments without cutting off the entire
air supply system.
F0A02.ai
Air supply pipe
Shut-off valve
Air header pipe
Air filter
Supply Regulator
Unregulated air supply
Samp
To instrument
Figure A.2 Example of Air Supply System (for
Field-Mounting Instruments)
(3) Air supply System for Field-Mounted
Instruments
• Supply Air
Clean, dry air is required. An aftercooler, filter,
air drier are used to eliminate water, oil, and
other contaminants.
• Air Supply Header (Air Header)
The air header that supplies air to a series
of instruments is installed with a minimum
downward pitch of 10 mm/m (1/100) so that
moisture and oil entrapped in the header can be
discharged.
• Air Supply Piping
An air supply pipe connected to an instrument
is branched from the upper part of an air header
to prevent moisture entry. Even if this is not
possible, an air supply pipe should be branched
from the side of the air header, i.e., it must not
be branched from the bottom part of the header.
It is recommended that an air supply pipe be
provided with a shut-off valve so that individual
instruments can be removed.
• Air Filter
A filter removes moisture, oil, and other
contaminants that cannot be removed by
the main air supply system. In general a
cock installed at the bottom of a filter is
opened to discharge moisture, oil, and other
contaminants. If the amount of moisture and oil
is large, increase the number of draining times.
The above-noted methods and units are an
example and there are other various methods
and units. Use a method and units suitable for the
process type to supply clean, dry air to instruments.
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