3.4
Vent-valve connection and control
3.4.1
Vent configurations
When you design your system and when you install a vent-valve, take note of the information in
Sections 1.3 and 2.3. You can vent the EXT250M pump and your vacuum system by any of the
following methods:
·
Use the manual vent-valve and vent-restrictor supplied.
·
Use the manual vent-valve and a different vent-restrictor (see Section 7.4.8).
·
Use a TAV solenoid vent-valve accessory (see Section 7) in place of the manual vent-valve,
together with a vent-restrictor, if necessary.
·
Use a TAV vent-valve connected to a convenient flange on your vacuum system, with a
vent-restrictor, if necessary.
·
Use an alternative valve connected to your vacuum system, together with a vent-restrictor if
necessary.
If you want to open the manual vent-valve when the pump speed is above 50% of full rotational
speed, you must ensure that you have a suitable vent-restrictor fitted to suit your vacuum
system: refer to Tables 4 and 5. If you do not have a suitable vent-restrictor fitted, you must only
open the vent-valve after the EXT pump speed has fallen to 50% of full rotational speed. If you
use the TAV vent-valve, you can only vent the EXT pump when it is at full rotational speed if the
vacuum system has a volume of 10 litres or more. If the volume of your vacuum system is less
than 10 litres, you must fit a suitable vent-restrictor to the TAV vent-valve. If you do not fit a
suitable vent-restrictor, you must only open the vent-valve to vent the EXT pump after the EXT
pump speed has fallen to 50% of full rotational speed.
If you use the EXC Controller to control your TAV vent-valve, you can configure the Controller
to open the vent-valve after the EXT pump speed has fallen to below 50% of full rotational speed:
do not select the ‘Vent On Stop’ option (refer to the EXC Controller instruction manual for more
information).
If you use another vent-valve, fit a suitable vent-restrictor to the inlet of your vent-valve (see
Tables 4 and 5). If you cannot fit a vent-restrictor to your vent-valve, you must open the
vent-valve only after the speed of the EXT pump has fallen to 50% of full rotational speed.
If you connect the vent-valve to your vacuum system, select a point upstream of the EXT pump to
prevent backstreaming of oil from the backing pump. Do not connect the vent-valve to the
backing pipeline. Connect the inlet of the vent-valve to the vent gas supply (refer to Section 2.3
for the vent gas specification).
EXT250M Turbomolecular Pump
16
