© Edwards Limited 2008. All rights reserved.
Page 21
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Installation
B722-20-880 Issue D
3.5
Purge gas connection (EXT255H 24 V and EXT255Hi 24 V only)
3.5.1
Connect the purge gas
To supply a purge gas to the pump, remove the manual purge-valve/plug fitted in the purge-port, fit a vent-port
adaptor (see
) to the purge-port and connect the purge gas supply to the vent-port adaptor. The purge
gas must comply with the specification given in
.
The flow rate of the purge gas must be limited to the allowed range, also specified in
. To limit the flow
rate, use a flow controller or a pressure regulator and calibrated flow restrictor. The PRX10 purge restrictor accessory
(see
) is suitable for this purpose. Adjust the PRX10 as described in the instruction manual supplied with
the accessory.
3.5.2
Recommended purge gas flow
The recommended purge gas flow for typical applications is 25 sccm (0.42 mbar l s
-1
, 42 Pa l s
-1
). This flow will protect
the pump when pumping oxygen in concentrations above 20% by volume.
3.6
Electrical installation
Always make the electrical connections to the EXT pump after the pump has been installed on your vacuum system.
The EXT pump should be electrically bonded to earth (ground) using the connection provided (see
).
3.6.1
EXDC drive module
There are two EXDC drive modules, the EXDC80 24 V and the EXDC160 24V. The EXDC80 24 V drive should be used in
conjunction with the EXT70H/Hi 24 V pumps - an EXDC160 should not be used with this family of pumps. It is
recommended that the EXT255H/Hi 24 V pumps are driven by the EXDC160 24 V module. However an EXDC80 24 V
may be used, although this will result in significantly extended ramp times and reduced performance.
Fit the connector on the EXDC Drive Module directly to the 19-way connector on the EXT pump.
The EXDC Drive Module is designed to allow a pumping system to be configured in a variety of ways. Refer to the
EXDC Drive Module instruction manual to complete the electrical installation.
CAUTION
Do not disconnect or connect the EXDC drive module while the pump is rotating. If you do, you may damage the
drive module.
Table 4 - Vent-restrictor orifice diameter (with atmospheric pressure at the inlet of the vent-valve)
Vacuum system volume (l)
Orifice diameter (mm)
< 20
≤
1.0
< 10
≤
0.7
< 5
≤
0.5
< 2
≤
0.35
