4230 Flow Meter
Section 5 Maintenance and Service
5-12
Figure 5-6 4230 Bubbler System Pressure Control
A fixed set-point pressure switch monitors air pressure in the
tank. The reference side of this differential pressure switch con-
nects to the bubble line. When the pressure in the tank falls
below 3.5 psig above the water pressure being measured, the
pressure switch turns the pump on for a fixed period of time.
Thus, the system maintains pressure in the tank at approxi-
mately 3.5 psig above the current water pressure.
5.7.2 Air Output to Bubble
Line
The output from the air supply tank leads to the bubble line
tubing connector on the side of the case. The bubble line attaches
to the flow meter through this connector. The pressurized air in
the tank can take two possible paths to the bubble line. The
normal route is through the Bubble Rate Adjust valve. This
adjustable, fine-metering valve controls the rate of air escaping
from the bubble line, establishing the bubble rate. The
adjustment knob of this valve is on the outside of the flow meter
case, allowing external adjustment of the bubble rate.
5.7.3 Purge The other path air can take to reach the bubble line is through
the bypass Purge valve. Purge is an electrically-operated valve.
When this valve turns on, air bypasses the Bubble Rate Adjust
valve and discharges directly into the bubble line. This valve also
opens momentarily to release bursts of air when the pressure
transducer detects a rapidly rising liquid level.
The flow meter normally operates with a battery-saving low
bubble rate, but these air bursts allow fast response to a sharply
rising liquid level. This quick-response feature is called Super
Bubble.
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