Gas Purges; Gas-Ballast Control - Edwards E2M28 Instruction Manual

A373-10-880 Issue T
4.1.3

Gas purges

If using inert gas purges to dilute dangerous gases to a safe level, ensure that the pump will shut
down if an inert gas supply fails.
Obey the instructions and take note of the precautions given below, to ensure that pumped gases
do not enter their flammable ranges.
Switch on the inert gas purge to remove air from the pump and the exhaust pipeline before the process starts. Switch
off the purge flow at the end of the process only after any remaining flammable gases or vapours have been purged
from the pump and exhaust pipeline.
If liquids that produce flammable vapours could be present in the pump foreline, then the inert gas purge to the
pump should be left on all the time this liquid is present. Flammable liquids could be present in the foreline as a
result of condensation, or may be carried over from the process.
When calculating the flow rate of inert gas required for dilution, consider the maximum flow rate for the flammable
gases/vapours that could occur. For example, if a mass flow controller is used to supply flammable gases to the
process, assume a flow rate for flammable gases that could arise if the mass flow controller is fully open.
Continually measure the inert gas purge flow rate. If the flow rate falls below that required, stop the flow of
flammable gases or vapours into the pump.
Note: Edwards recommends obtaining and reading the Vacuum Pump and Vacuum System Safety manual
(publication number P400-40-100), available from Edwards or the supplier.
4.2

Gas-ballast control

Use the gas-ballast control
and to provide an additional oil-feed to the pump mechanism.
Use the gas-ballast control closed:
To achieve ultimate vacuum.

To pump dry gases.

Turn the gas-ballast control six turns anti-clockwise to open it fully. Use the gas-ballast control open:
To pump high concentrations of condensable vapour.

To decontaminate the oil.

When operating the pump with the gas-ballast control open, there will be an increased rate of oil loss from the pump.
Ideally, a mist filter and oil return kit should be used on clean applications.
Page 22
WARNING
WARNING
Figure 1, item 3) to change the flow of gas-ballast into the low vacuum stage of the pump,
Edwards and the Edwards logo are trademarks of Edwards Limited.
© Edwards Limited 2014. All rights reserved.