PART FOUR - SERVICE AND MAINTENANCE
SECTION 2 - PRESERVING MEASUREMENT ACCURACY
Accu4™ Low-range Turbidimeter System
Rev. 2-300
86
S
ECTION
2
2.1 Eliminating Bubbles in
Sensor Flow Chamber
Restricting
Sensor Outlet
Using an External
Bubble Trap
Two kinds of air or gas bubbles may exist in the sample:
those that can be seen and those that cannot. Visible bub-
bles are created by mixing liquid and air. For example,
water falling down or flowing through a pipe containing air
will form bubbles. Bubbles that cannot be seen in liquid, but
that do form and become visible in the sensor flow chamber
are absorbed in the liquid. This can occur naturally or be
the result of human intervention such as when ozone is in-
jected into water to act as a disinfectant.
To remove visible bubbles in liquid, a bubble trap may be
necessary. To minimize the effect of bubbles that cannot be
seen, but that eventually form on the flow chamber win-
dows, the liquid must be pressurized while it is being
measured. This is easily accomplished by restricting the
outflow from the Model 8320 turbidity sensor. To do this:
1.
Maintain the flow rate through the sensor within its
specified limits (0.05 to 7 GPM).
2.
Install a flow restrictor into the sensor outlet line and
adjust it until flow is slightly reduced.
3.
Close the 3-way valve to stop flow through the sensor.
4.
Drain the flow chamber using the 3-way valve and cali-
bration funnel.
5.
Slowly open the 3-way valve to allow the flow chamber
to slowly fill with sample liquid.
The above procedure should ensure bubble-free operation.
For low sample flow rates (less than 0.5 GPM), the Model
8320 turbidity sensor has a built-in bubble trap to minimize
air accumulation in the flow chamber. For higher flow rates,
it is recommended to use an external bubble trap/stilling
chamber (GLI part number 80A1020) to collect and vent off
air or gas from the liquid. The bubble trap must be installed
vertically (air vent upward) and upstream of the sensor.
(The air vent on GLI’s external bubble trap/stilling chamber
can be opened or closed. Bubbles remain in solution when
the vent is closed, or are vented off when it is opened.)
Periodically, it is recommended to remove the bubble trap
drain plug to allow any accumulated sediment sludge to drain.
PRESERVING MEASUREMENT ACCURACY
