© Edwards Limited 2013. All rights reserved. Page 23
Edwards and the Edwards logo are trademarks of Edwards Limited.
Installation
B722-40-880 Issue F
Edwards recommends that the following requirements be met to ensure the pump remains secure in the event of a
total pump seizure:
Use this method of fixing the pump if it supports the weight of the vacuum system. The weight of the vacuum system
must be no more than 10 kg for EXT75DX and 20 kg for EXT255DX.
3.3.5 Backing connection
Do not use the DX pumps 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 may reduce the life of the bearings.
Use suitable vacuum tubing and connectors to connect the NW flange of the backing port to the backing pump. If
necessary, use flexible pipe or bellows to reduce the transmission of vibration from the backing pump to the DX
pump.
Edwards recommends using an Edwards EM, RV or XDS Scroll backing pump. The recommended size of backing pump
required is indicated in Table 5. A larger or smaller backing pump may also be suitable, depending upon the intended
application.
The DX pumps are 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. Refer to Table 5 and Section 2.1.
3.3.6 Interstage connection (iDX variants only)
Use suitable vacuum tube and connectors to connect the interstage port to the vacuum system or to the outlet flange
of another turbo or compound turbomolecular pump (if using an iDX pump to back another pump). Leave the inlet
strainer in the interstage port, unless it is certain that debris cannot be drawn into the interstage port.
Note: The EXT75iDX with NW16 interstage port is not supplied with an inlet strainer fitted.
Support must withstand a destructive torque of: 333 Nm (EXT75DX)
620 Nm (EXT255DX)
Fixing screws: To ISO898-1 strength class 12.9
(nom. tensile strength 1200 MPa)
Screw engagement length: 6 mm minimum
Fastening torque: 6 Nm (0.61 kgf.m) (EXT75DX)
12 Nm (1.22 kgf.m) (EXT255DX)
Ensure safe ducting of the backing line if oil mist or hazardous substances are present.
To avoid over-pressurising the pump, the exhaust line should be restricted when venting from a
positive pressure gas supply.
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