Fault FInDIng
Any service or repair work should only be carried out by a trained electronic or electro mechanical
technicians. Untrained personnel should not attempt to dismantle this equipment.
a) If the cut-out indicator fails to extinguish when the reset switch is depressed, check the temperature
of the fluidised bath to determine whether the bath has overheated and operated the temperature
cut-out. Check the setting of the over temperature cut-out which is situated within the electrical
control console. The over temperature cut-out is factory set to a maximum temperature of 630°C.
The cut-out can be re-set by depressing the red knob on the bottom of the cut-out.
To over-ride the door safety switch pull the knob down slightly and out.
Also check that compressed air is being supplied to the fluidised bath and that the air pressure
switch is being held in the on position. When operating correctly the air pressure regulator situated
within the pneumatic control console should be set at 204k Pa (30psi) and the bath should be
fluidised.
b) If the fluidised bath fails to reach its operating temperature or the heat-up rate decreases, check the
level of fluidisation. Where an air flowmeter is fitted, check that the air flow rate agrees with the
recommended values, and in any case check that the fluidised bed is evenly fluidised with bubbles
of approximately 50mm diameter.
Also check that the heater elements are functioning correctly. Four heater elements are fitted which
produce a total heater power of 9kW. The heater elements are individually terminated within the
control console (see attached circuit diagrams for wiring details).
To inspect the heater elements, remove the inner container from the outer wrapper. The heater
elements are of the semi-embedded type.
c)
If the fluidisation within the bath deteriorates, check the compressed air supply and the air filter
assembly. Replace the air filter elements if necessary. Where a flowmeter is fitted, check the air flow
rates correspond with the recommended values.
Ensure that the air pressure regulator is set at 204kPa (30 psi).
If the fluidisation in the bath does not produce satisfactory results when using the correct air flow
rates, the condition of the porous plate in the base of the fluidised bath must be suspected.
An initial remedy is to operate the fluidised bath at approximately 550oC for a period of at least one
hour to allow any accumulated residue in the bath to be decomposed. However, if the fault
continues the bath should be emptied and the porous plate examined.
The fluidised bath must only be emptied when the bath is cold.
To empty the bath, use a scoop to remove the alundum, when the unit is fluidised. A small quantity
of fluidising medium will remain in the base of the bath; this should be removed using a vacuum
cleaner.
When the bath is empty, the stainless steel porous plate may be examined for any sign of damage
caused by the accumulation of plastic residue, distortion, or corrosion. Partially blocked areas of the
porous plate can be detected if the bath is fluidised with a small quantity of fresh fluidising
medium.
If the porous plate assembly is blocked any residue on the bolt heads can be chipped off. The bolt
heads should be rotated to ensure all bolts move freely and allow full air flow through the plate.
Reset the central temperature monitor to a temperature of 200°C which will energise the upper
solenoid valve. Adjust the upper valve until the total indicated air flow rate is approximately 160 l/
min.
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