© Edwards Limited 2015. All rights reserved. Page 17
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Operation
A352-03-880 Issue B
4 Operation
4.1 Gas ballast control
Use the gas ballast control (Figures 1, 2, and 3, item 6) to change the amount of air (or inert gas) introduced into the
pump. Use of the gas ballast will prevent the condensation of vapours in the pump. The condensed vapours would
contaminate the oil.
Turn the gas ballast control clockwise to close. Use the gas ballast control fully closed:
to achieve ultimate vacuum
to pump dry gases.
Turn the gas ballast control anticlockwise (90 degree movement) to open. Use the gas ballast control fully open:
to pump high concentrations of condensable vapour
to decontaminate the oil.
When operating the pump with the gas ballast control open, there is an increased rate of oil loss from the pump.
4.2 Start up procedure
If the oil is contaminated, or if the pump temperature is below 12 °C, or if the supply voltage is more than 10% below
the lowest voltage specified for the motor, the pump may operate at reduced speed for a few minutes.
1. Switch on the electrical supply to the pump.
2. Check that the oil level in the sight glass drops slightly (3 to 5 mm) after start up. This shows that the pump has
primed with oil.
3. If the pump fails to prime, operate the pump with the inlet open to atmosphere for approximately 30 seconds,
then isolate the inlet and check that the oil level drops 3-5 mm.
4. Edwards recommend strongly to limit starting of the pump to no more than 5 or 6 per hour. If the process
requires it, utilisation of an inlet valve and to let the pump run continuously is recommended.
4.3 To achieve ultimate vacuum
If the pump does not achieve the performance specified in Section 2, make sure that this is not due to the system
design before contacting the supplier or Edwards for advice. In particular, the vapour pressure of all materials used
in the vacuum system, including pump oil, must be much lower than the specified ultimate vacuum of the pump.
Refer to Section 5.12.2 for a list of possible causes for failure to achieve the specified performance. The most
common causes are:
The pressure measurement technique or gauge head is unsuitable or the gauge head is faulty.
An oil other than the recommended oil was used and the vapour pressure of the oil is higher than the
specified ultimate vacuum of the pump.
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