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PUMP USED WITH CORROSIVE GASES
CAUTION
To prevent bearing damage, the integrated purge
valve is foreseen for a gas flow rate of 20 sccm
(0.34 mbar l/s). Please contact Varian for specific
applications. The recommended gas purge flow
maintains a pressure into the pump body higher than
the forevacuum pressure.
Gas Purge
To prevent damage to the bearings, an inert gas
must flow into the pump body around the upper
bearing towards the forevacuum line.
The inert purge gas (e. g. nitrogen, argon) is sup-
plied to the pump through the integrated purge
valve. A pressure regulator can be installed be-
tween the purge valve and the gas purge source.
Adjust the pressure regulator in order to obtain the
necessary gas purge flow rate of 20 sccm.
The standard gas purge may be supplied with 1
atm (15 psig) to get 20 sccm.
Gas Purge Vent Device Description
A gas purge vent device (model 969-9116) is
available to prevent the pump from clogging
whenever it is used with condensable gases.
When the gas purge vent device is properly in-
stalled on the pump (see the relevant manual in-
structions), it provides a continuos gas purge flow
through the standard pump gas purge port and a
continuos Macrotorr cleaning inert gas flow
through the standard pump vent port to maintain
the pump channels in clean conditions. This flow is
calibrated not to affect the pump inlet pressure.
When the pump is stopped, a double vent flow is
injected into the pump through the vent and gas
purge port to keep a positive difference of pres-
sure through the pump bearings, protecting them
from contamination with corrosive gases even dur-
ing a pump sudden vent.
A proper valve opening sequence is provided by
the manifold control unit.
The gas purge vent device is provided with (see
the following figure):
• a valved manifold with two NW10 ports (item 1);
• an electronic driving unit (item 2);
• a gas purge port NW10 flange - M12 adapter +
center ring (item 3);
• a vent port NW10 flange - M8 adapter + center
ring (item 4).
Gas Purge Vent Device
An hard switch signal is present on the purge vent
device control unit to stop the backing pump with
the proper timing during the vent cycle.
Solid State Flowmeter Installation
A gas purge valve is integrated to protect the
pump bearings against particulate and corrosive
gases that could move into the pump.
To the purge valve can be connected a solid state
flowmeter model 969-9114 (see the following figure)
or model 969-9115, operating in the range from 0 to
150 SCCM with Nitrogen, and from 0 to 125 SCCM
with Argon, that connected to the controller can
monitor the flow of the protective gas purge.
The following figure shows the connector of the
flowmeter to the controller.
33
TECHNICAL INFORMATION
87-900-915-01(E)
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