B722-20-880 Issue D
Page 20 © Edwards Limited 2008. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Installation
3.3.5 Backing connection
Use suitable vacuum tubing and connectors to connect the NW flange of the backing-port to your backing-pump. If
necessary, use flexible pipe or bellows to reduce the transmission of vibration from the backing-pump to the EXT
pump.
It is recommended that you use an Edwards EM or RV backing-pump. The minimum size of the backing-pump required
is given in Table 1 and 2. It may be necessary to use a larger backing-pump if the pump is run at a high inlet pressure
or high throughput, or if an EXT255H/Hi 24 V pump is purged with more than 25 sccm (0.42 mbar l s
-1
, 42 Pa l s
-1
) of
purge gas.
Do not use the EXT pump with a backing pressure below 1 x 10
-4
mbar (1 x 10
-2
Pa). Lower backing pressures will
increase the evaporation rate of the lubricating oil and so will reduce the life of the bearings.
3.3.6 Interstage connection ((EXT70Hi 24 V and EXT255Hi 24 V only)
Use suitable vacuum tube and connectors to connect the interstage-port to the vacuum system or to the outlet flange
of another turbomolecular pump (if using the EXT70Hi 24 V or EXT255Hi 24 V pump to back another turbomolecular
pump). Leave the inlet-strainer in the interstage-port of the EXT255Hi 24 V pump, unless you are sure that debris
cannot be drawn into the interstage-port.
3.4 Vent-valve connection and control
When designing your system and when you install a vent-valve, take note of the information in Section 1.3 and 2.3.
The EXT pump and vacuum system can be vented by any of the following methods:
z Use the manual vent-valve supplied. Take care not to open the manual vent valve too quickly (see below).
z Use a TAV5 or TAV6 solenoid vent-valve accessory (see Section 7) in place of the manual vent-valve.
z Use a TAV5 or TAV6 solenoid vent-valve connected to a convenient flange on your vacuum system.
z Use an alternative valve connected to the vacuum system.
If using the manual vent-valve, the vent-valve must be opened only after the EXT pump speed has fallen to 50% of
full rotational speed.
If using the TAV5 vent-valve, the pump may only be vented when it is at full speed if the vacuum system has a volume
of 5 litres or more. If using the TAV6 vent-valve, the pump may only be vented when it is at full speed if the vacuum
system has a volume of 10 litres or more. If the volume of your vacuum system is less than 5 litres (when using a TAV5
vent-valve), or if the volume of your vacuum system is less than 10 litres (when using a TAV6 vent-valve), you can
incorporate a suitable vent-restrictor (see Table 4) and vent the pump when it is at full speed.
If using another vent-valve, ensure that a suitable vent-restrictor is fitted to your vacuum system to limit the rate of
pressure rise: refer to Table 5. If you do not fit a suitable vent-restrictor, 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 a 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).
Note: If you use a vent-restrictor, you may find that the time required to vent your vacuum system is unacceptably
long. You may be able to reduce the vent time if you use a vent-valve without a vent-restrictor and wait
until the pump speed has fallen to 50% of full rotational speed before you open the vent-valve.
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