4230 Flow Meter
Section 3 Installation
3-5
3.2.6 External 12 Volt Direct
Current Source
You can also power the flow meter from an external 12 VDC
source, such as an automotive, motorcycle, or marine battery.
Many people have found that a deep-cycle marine/RV battery is
particularly well-suited to this application. However, you will
have to mount batteries of this type externally, as they are too
large to fit on top of the flow meter. Isco offers a special optional
connect cable to power the flow meter from a separate battery.
Mount the battery securely, in an upright position, so it will not
inadvertently tip over, or have its cable easily pulled off. As
advised previously for the nickel-cadmium battery, do not check
the charge condition of lead-acid batteries by “sparking” the
output cables (momentarily shorting the wires together).
CAUTION
Be sure of proper polarity before attaching clips to the battery.
Never attach the flow meter to a source of unknown polarity or
voltage. If in doubt, check with a reliable DC voltmeter. Never
attach the flow meter directly to an AC power source regard-
less of circumstances. Charge the battery in accordance with
the manufacturer's instructions.
3.3 Bubble Rate The Bubble Rate Adjust valve, located on the side of the case, is a
“needle” type valve that controls the rate air is fed from the res-
ervoir into the bubble line and the rate the bubbles are released
into the flow stream. Turning the valve knob counterclockwise
causes the bubble rate to increase. Turning the knob clockwise
causes the bubble rate to decrease. Turning the knob clockwise
until it stops will completely shut off the air supply to the bubble
line.
CAUTION
Do not use anything but your fingers to turn the Bubble Rate
Adjust valve. The needle and seat inside the valve are very
small and you can damage or break them if you use tools or
force to close the valve. Once you have set the valve properly,
do not overtighten the hex screw that locks the adjustment
knob or you may strip the threads or ruin the Allen wrench.
3.3.1 Setting the Bubble Rate The recommended bubble rate is approximately one bubble per
second. For relatively clean flow streams, this bubble rate pro-
vides adequate sensitivity with reasonable power consumption.
For flow streams with suspended solids (for example, domestic
raw sewage or streams with a high grease content), two bubbles
per second may help prevent plugging of the bubble line at the
expense of higher power consumption.
3.3.2 Bubble Rate and Power
Consumption
Power consumption by the flow meter's air pump is directly
related to the setting of the bubble rate and the inside diameter
of the bubble line. At one bubble per second, the
1
/8" (0.32 cm) ID
bubble line uses about 2
1
/2 times more power for the air pump
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