B344-21-880 Issue N
Page 34 © Edwards Limited 2007. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Operation
4.3 Re-admission of air to your vacuum system
1. Close the high-vacuum isolation-valve and ensure the backing/roughing-valve is in ‘Backing’ mode.
2. Open the chamber air-admittance valve.
4.4 Re-evacuation of your vacuum system
1. Close the chamber air-admittance valve and any other openings to atmosphere.
2. Select ‘Roughing’ on the combined backing/roughing-valve.
3. When a system pressure of 0.3 mbar (3 x 10
1
Pa) or lower is reached, select ‘Backing’.
4. Open the high-vacuum isolation-valve slowly; if you open the valve too quickly, you can stall the pump.
4.5 Pump shut-down
The following method of shut-down ensures that the Diffstak is left evacuated; this prevents absorbtion of air by the
pump fluid. When you subsequently start up, evacuate the system through the roughing pipeline to a pressure of
0.3 mbar (3 x 10
1
Pa) or lower before you open the backing-valve.
1. Close the high-vacuum isolation-valve. Switch off the Diffstak heater and allow the pump to cool. If you do not
allow the pump to cool before you admit air into the pump, on re-evacuation the pump fluid will superheat and
evolve vapour which will pass into the backing pipeline.
2. Select ‘Isolation’ on the combined backing/roughing-valve. (If pneumatically-operated valves are fitted this will
require a control circuit with two electropneumatic control-valves. Suitable control-valves are listed in
Section 7).
3. Open the rotary backing pump air-admittance valve, then switch off the backing pump. Do not switch off the
backing pump unless air is admitted into the backing pipeline, or backing pump oil may be drawn into the
backing pipeline.
4. Turn off the cooling-water supply.
If the cooling-water supply fails during operation, steam or water may be ejected from the
couplings if they are disconnected.
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