Instruction manual

EXT Split Flow Compound Turbomolecular Pumps
INSTALLATION
PAGE
16
Issue F 16 Mar 07
We recommend that you use a BOC Edwards RV Backing-Pump. The minimum size of the backing- pump
required is given in Table 4. You may have to use a larger backing-pump if you run the pump at a high
inlet pressure. The EXT70/200H and EXT200/200H Split Flow Pumps are also suitable for use with
diaphragm backing-pumps although the effect of higher backing pressure on the pump’s performance and
cooling requirements should be noted (see Table 1 and Section 3.6).
3.3.5 Interstage connection (Hi pump variants only)
Use suitable vacuum tube and connectors to connect the interstage-port to your vacuum system or to
the outlet flange of another turbo molecular pump. Leave the inlet-strainer in the interstage- port, unless
you are sure that debris cannot be drawn into the interstage-port.
3.4 Vent options, vent valve connection and control
To maintain the cleanliness of your vacuum system, we recommend that, whenever you switch the pump
off, you vent the pump (or vacuum system) when the speed of the EXT Split Flow Pump is between full
rotational speed and 50% of full rotational speed. At and above 50% of full rotational speed, the rotor
spins fast enough to suppress any backstreaming of hydrocarbon oil from your backing pump. Venting
may be accomplished by one of the following methods.
• Use a TAV5 or TAV6 solenoid vent-valve accessory (see Section 7) in place of the manual vent-
valve.
• Use a TAV5 or TAV6 solenoid vent-valve connected to a convenient flange on your vacuum system.
• Use an alternative valve, with an appropriate restriction, connected to your vacuum system. For
further details contact BOC Edwards.
However, if you manually vent the pump when it is at full rotational speed and the rate of pressure rise
is too high, the pump life may be reduced. When using the manual vent valve supplied, we recommend
that you either limit the vent or only open the vent-valve after the EXT Split Flow Pump speed has fallen
to 50% of full rotational speed.
Do not vent from the backing line, this may lead to contamination. If you vent into your vacuum system,
select a point upstream of the pump, to prevent oil backstreaming from the backing line.
If you use the TAV5 or TAV6 vent-valve you can control it using an EXC Controller, or by other
methods. Table 6 gives an indication of the appropriate orifice size to be fitted to the vent valve for given
vacuum system volumes in order that the vent rate is kept within the limits given in Section 2.3.
CAUTION
Do not use the EXT Split Flow Pump with a backing pressure below 5 x 10
-4
mbar (5 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.
Vacuum system volume (1) Orifice diameter (mm)
< 20 < 1.0
< 10 < 0.7
< 5 < 0.5
< 2 < 0.35
Table 6 - Vent-restrictor orifice diameter (with atmospheric pressure at the inlet of the vent-valve)