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1)
Close the shut off valve at the base of the reservoir.
2)
Disconnect one of the tubes and then reconnect it to the base of a filling tank that is filled
with de-aired liquid.
3)
The second tube is disconnected and attached to the base of an auxiliary reservoir. (For tubes
longer than 200 meters (650 feet) it is recommended that a vacuum pump be attached to the
top of the auxiliary reservoir. This will speed up the flushing process.)
4)
Connect a nitrogen cylinder with regulator to the top of the filling tank.
5)
Start the vacuum pump running then open the valve at the bottom of the pressure tank.
6)
Adjust the nitrogen pressure until the settlement sensor reads at its maximum range value on
the Readout Box. (See Section 3 for Readout instructions.) Be careful not to over range the
sensor by more than 20%.
CAUTION! Do not allow the nitrogen pressure to exceed the
pressure rating marked on the outside of the filling tank (usually 100 psi (700 kPa).
Failure to observe this precaution could result in injury.
7)
Continue flushing until all the old liquid has been removed. (As flushing proceeds, the
auxiliary reservoir may need to be emptied periodically.)
8)
Store the flushed liquid in a container for later disposal. Do not allow any liquid to enter the
vacuum pump as this could ruin it.
9)
When flushing is complete, reconnect the fluid lines to the base of the reservoir.
Be careful
not to introduce air bubbles during this process.
7. PURGING THE VENT LINES
The vent line must remain open at all times; it connects the inside of the sensor to the space
above the reservoir. Any blockage of the vent line due to pinching, dirt, or moisture will cause
false readings that fluctuate and/or are sensitive to temperatures.
Blockages due to pinched tubes can be confirmed by applying a vacuum to the vent line and
observing the reading on the sensor. If the sensor does not respond the tube is blocked by dirt or
pinched, and this might be correctable if the blockage is accessible. Blockages due to moisture
and condensation can be purged using a vacuum pump to evacuate the vent line. As the vacuum
is applied watch for signs of water in the vent line. When the vacuum has stabilized, stop the
pump, disconnect the vent line, and quickly reattach either a desiccant chamber containing fresh
desiccant, or a cylinder of dry nitrogen. This ensures that the gas drawn back into the vent line is
dry. Make sure the vent line connection is open between the desiccant chamber (or vent line
manifold) and the top of the reservoir.
