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Astell Autoclaves/Sterilisers – AMB220 | AMB230 | AMB240 | AMB420 | AMB430 | AMB440 | AMA240 | AMA440
PRESSURE SWITCH INTERLOCK
Typical view of pressure switch
The fault system should indicate a pressure switch fault
this usually indicates a bad pressure adjustment or drift,
and is seldom a pressure switch failure.
The pressure switch should release at approx. + 0.1 bar
Due to age or stress this setting may drift.
The system monitors this switch as a safety feature to
prevent opening the chamber if the pressure exceeds
0.1bar.
Observe the pressure and temperature displays.
If
• The Pressure displayed is close to Atmospheric
pressure (e.g. around 0Bar)
And
• The temperature is near to room temperature
And
• The display still shows the fault as above
Then, the Pressure switch may be out of adjustment.
It may resolve itself if left for 1-2 hrs. to cool down.
If this continues, the pressure switch should be checked
and adjusted - please contact your service agent or Astell
Scientific for advice.
WATER LEVEL SENSOR PROBLEMS
An example fault here is that the system starts without
taking on water. This occurs if the water level sensor is
already falsely detecting sufficient water present.
A correctly installed and functioning system cannot start
to heat until the correct water level is present in the
chamber, but it is important that the sterilizer is installed
with the feet on a horizontal surface. On frontload models
the front of the machine is higher than the rear so the
chamber is tipped backwards.
The usual cause for this is that the water is not entering at
the start to the correct level because the chamber water
level sensor has been damaged or is missing or is being
touched by some other conductive object.
Inspect the water level sensor fitted through the rear or
on top load models, through the side at the base of the
chamber. This is the 3mm thick brass strip approx. 20mm
wide, pointing down towards the water. When the water
reaches the tip of this it makes contact and the electrical
conductivity of the water completes the circuit to the
boiler which is sensed to measure the water level.
Possible problems
• That the sensor strip is bent and touching something
metal
• The load supports are defective and a metal load
container or shelf is touching and shorting out the
sensor.
• The sensor is dirty. Congealed effluent from the load
has coated the insulator shorting the sensor out to the
boiler wall.
Check that nothing is touching the sensor and that it and
the insulator are clean. A Scotch-Brite pad is useful for
this. If the problem continues service attention will be
required.
OVERHEAT FAULT
If there is a water level problem or a valve sticks open,
blowing out the water and the system goes to boil dry,
then the heater will be exposed and the over temperature
thermostat will start to operate. This will take over control
and shut down the heater until the temperature falls.
This will cause the temperature to vary very widely up and
down as the heater cuts in and out.
The pressure will not match the temperature
E.g. the chamber might be above 100°C but the pressure
might be zero or much lower than normal.
Service attention will be required.