PNEUMATIC CONTROL FUNDAMENTALS
ENGINEERING MANUAL OF AUTOMATIC CONTROL
89
The Discharge Air Temperature Indicator is fed from the
pneumatic discharge air temperature sensor and the Three-Way
Valve Gauge is fed from the valve control line.
When pneumatic automation panels are located local to the
HVAC system, they are usually connected with 6 mm plastic
tubing. When there are many lines at extended lengths, smaller
diameter plastic tubing may be preferable to save space and
maintain responsiveness. When the panel devices are remote,
the air supply should be sourced remotely to avoid pressure
losses due to long flow lines. The switching air may be from
the automation panel or it may be fed via a remote restrictor
and piped in an exhaust configuration.
PNEUMATIC CENTRALIZATION
Building environmental systems may be pneumatically
automated to any degree desired. Figure 73 provides an
example of the front of a pneumatic automation panel. This
panel contains pneumatic controls and may be local to the
controlled HVAC system, or it may be located centrally in a
more convenient location.
In this example, the on-off toggle switch starts and stops the
fan. The toggle switch may be electric, or pneumatic with a
Pneumatic-Electric (P/E) relay.
Two pneumatic “target” gauges are shown for the outside air
damper and the supply fan. The ON/OFF Supply Fan Gauge is
fed from a fan proof-of-flow relay, and the OPEN/CLOSED
Damper Gauge is fed from the damper control line.
Fig. 73. Pneumatic Centralization
0
70
140
200
35
30
25
20
15
10
5
0
-5
-10
-15
kPa
DISCHARGE AIR
TEMPERATURE
O
P
E
N
O
N
RETURN
AIR
SUPPLY
FAN
OUTSIDE
AIR
AHU 6
ON OFF
COOLING
COIL
M15142
30-75 kPa
NORMALLY
OPEN
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