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5.1.2 Gas purges
WARNING:
If using inert gas purges to dilute dangerous gases to a safe level, ensure that the
pump is shut down if an inert gas supply fails.
WARNING:
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:
We recommend obtaining and reading the Vacuum Pump and Vacuum System Safety
manual (publication number P40040100), available from us or the supplier.
5.2 How to use the pump controls
5.2.1 Introduction
Use the mode selector ( Figure: The RV pump , item 11) and the gas-ballast control
( Figure: The RV pump , item 5) to optimise the performance of the RV pump for the
application. The performance characteristics of the pump with the different control
settings are shown in Table: Performance data- High Vacuum mode and Table:
Performance data- High throughput mode . The position of both the mode selector and
the gas-ballast control can be changed when the pump is off or when the pump is
operating.
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A65201880_AA - Operation