3.3.4
Inlet connection and orientation
The EXT250M pump can be fixed to the vacuum system by the inlet-flange. The pump can be
mounted in any attitude. If the pump is mounted horizontally and you use a rotary vane pump
to back the EXT250M pump, the backing port must point vertically downwards (
±
20
o
) to reduce
the risk of contamination from the backing pump oil.
Make sure that the pump-inlet and all components fitted to the pump-inlet are clean and
dust-free. If the pump-inlet is not kept clean, the pump-down time may be increased.
The inlet-connection of the EXT250M pump is a CF flange or an ISO flange:
·
If the pump has a CF flange, use the copper compression gasket supplied with the pump and
use a full complement of bolts to connect the inlet-flange of the pump to the vacuum system.
·
If the pump has an ISO flange, use the BOC Edwards trapped ‘O’ ring supplied with the
pump and use a minimum of four claw clamps to connect the inlet-flange of the pump to the
vacuum system. Ensure that each claw clamp is tightened to a torque of 10 Nm or more.
Alternatively, use a rotatable collar and the trapped ‘O’ ring supplied with the pump to
connect the inlet-flange of the pump to the vacuum system; use a full complement of bolts
with the rotatable collar.
Ensure that no torque or other forces are transmitted to the pump from the vacuum system or the
associated pipelines.
If necessary, fit an inlet vibration isolator between the pump-inlet and the vacuum system: refer
to Section 7.4.6 for the Item Numbers, and refer to the instruction manual supplied with the
vibration isolator for installation details. If you fit a vibration isolator, you must securely fix the
base of the EXT250M pump as described in Section 3.3.3.
Note:
The first time you pump down the system to vacuum, you must re-tighten the bolts which secure
the inlet-flange.
3.3.5
Backing connection
Connect the backing-port to your backing-pump with suitable vacuum pipes and connectors. If
necessary, use flexible pipe or bellows to reduce the transmission of vibration from the
backing-pump to the EXT250M pump. To further reduce vibration from the backing-pump,
secure a mid-section of the flexible vacuum pipe to the floor or to a substantial mass.
We recommend that you use a BOC Edwards two-stage backing-pump. The backing-pump can
be controlled by the EXC300M Controller. The recommended size of the backing-pump required
is given in Table 2. You may have to use a larger backing-pump if you operate the pump with
high inlet pressure or high throughput or if you purge the pump with more than 25 sccm
(0.42 mbar l s
-1
, 42 Pa l s
-1
) of purge gas.
Use a foreline trap available from BOC Edwards as an accessory (see Section 7) to ensure that the
backing line is free from oil vapour. In addition, you can fit a backing pipeline isolation-valve
directly to the backing-pump. This valve totally isolates the EXT250M and, as the EXT250M is
oil-free, may be used in place of an isolation-valve at the pump-inlet.
EXT250M Turbomolecular Pump
15
