3.4.2
Remove and replace the vent-port VRX vent-restrictor
To remove the VRX vent-restrictor, refer to Figure 1 and use the following procedure.
1.
Remove the manual vent-valve (6) from the pump.
2.
The vent-restrictor (23) has an M3 tapped hole. Fit an M3 screw to the tapped hole, then pull
the screw to remove the vent-restrictor from the vent port.
To refit the vent-restrictor or fit a new vent-restrictor:
1.
Apply a light wipe of vacuum grease to the 'O' ring on the vent-restrictor (23).
2.
Fit an M3 screw to the tapped hole on the vent-restrictor (23) and push the vent-restrictor
fully into the vent-port.
3.
Remove the M3 screw, then refit and tighten the manual vent-valve (6).
3.5
Purge gas connection
3.5.1
Remove and replace the purge-port VRX vent-restrictor (if necessary)
If necessary use the following procedure to remove the VRX vent-restrictor in the purge-port
(Figure 3, item 4).
1.
Refer to Figure 6. Remove the blanking-plug (9) or any vacuum fittings from the purge-port.
2.
Fit a long M3 screw (M3 x 50 is suitable) to the tapped hole in the vent-restrictor (6), then pull
the screw to remove the vent-restrictor from the purge-port.
To refit the vent-restrictor or fit a new vent-restrictor:
1.
Refer to Figure 6. Fit a long M3 screw (M3 x 50 is suitable) to the tapped hole on the
vent-restrictor (6) and push the vent-restrictor fully into the purge-port. Ensure that the ‘O’
ring correctly seals the vent-restrictor in the purge-port.
2.
Remove the M3 screw, then fit or refit the vacuum fittings to the purge-port.
3.5.2
Connect the purge gas
Refer to Figure 6. If you want to supply a purge gas to the pump, remove the blanking-plug (9)
from the purge-port and connect your purge gas supply to the purge-port. Your purge gas must
comply with the specification given in Section 2.3.
You must limit the flow rate of the purge gas to the allowed range, also specified in Section 2.3.
Note that the VRX vent-restrictor (6) fitted to the purge-port will not limit the flow rate to a low
enough value for purge purposes. To limit the flow rate, use a flow controller or a pressure
regulator and calibrated flow restrictor. The PRX10 purge restrictor accessory (see Section 7.4) is
suitable for this purpose.
18
EXT250M Turbomolecular Pump
