Technical Services Group
Operating Procedure
Internal Use Only
Vacuum Drying of Core Samples and Fatigue Beams
OP475
Revision: 1.0 Date: July 2014 Page
SCOPE
This procedure describes the method for the vacuum drying of core samples and fatigue beams
REFERENCES
Nil
DEFINITIONS
Nil
APPARATUS AND MATERIALS
Vacuum pump able to achieve a minimum of -90 kPa
Large metal vacuum desiccator
On/off air tap
Indicator silica gel – green to orange
Pressure gauge or manometer with a range of - 100 kpa
Suitable vacuum air line hose
Racks that allow air to flow
Vacuum flask to be water trap
4.1 SET UP
As per diagram or similar:
DESICCATOR
Must be a vacuum desiccator large enough to accommodate 4 fatigue beams. The rack allows the moisture to exit the cores
Check that the rubber ring around the desiccator is not damaged. The top lid of the desiccator must be on square and centred and the front and back latches securely fasten.
5.0 PROCEDURE
The following procedure shall be followed.
Place dried silica gel inside the bottom of the desiccator
Place a rack on top of the silica gel.
Place the specimens in the Desiccator and place a cup with silica gel in with specimens.
Place the lid on the desiccator (make sure that the rubber ring around the desiccator is not damaged. The top lid of the desiccator must be on square and centred and the front and back latches are securely fastened)
Ensure that the air tap is open.
Turn the pump on.
Check that the pressure gauge is continuously increasing.
Leave the samples in the vacuum for a 4 hour drying period.
After 4 hours close the tap to the desiccator and turn the pump off.
RELEASING THE VACUUM SLOWLY AND SAFELY
Remove the vacuum hose from the desiccator. Use the end of the hose to depress the valve and slowly allow the air to vent into the desiccator.
Once the device has stopped venting remove the lid.
Samples are ready to be weighed.
After weighing the samples return them to the desiccator for another 2 hours to ensure that they are completely dry.
Reweigh the samples. If the difference between the two weights is significant (>0.5g) then return the samples to the desiccator for another 60 minutes.
If the samples have again lost a significant amount of weight return the samples to the desiccator for another hour and then reweigh. Repeat until the weight of the sample remains constant.
CALCULATIONS
Nil
REPORTING
Nil
NOTES ON THE METHOD
Always use freshly dried indicator silica gel during each drying cycle.
Maintain good serviceability of the vacuum pump.
Regularly inspect the oil in the pump for any water contamination and replace the oil if necessary.
Always use rated vacuum hose for the system as other plastic hose may collapse with increased vacuum.
Maintain dry indicator silica gel in the water trap flask connected before the vacuum pump.
Place the desiccator lid on a cushioned surface to protect hooks used to attach the locking latches.
Maintain the calibration of the vacuum gauge or manometer used in this system.
PRECISION
Nil
DOCUMENTATION
Nil
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