Edwards EXT Series User manual

B753-03-880
Issue F Original
Instruction Manual
EXT Compound Molecular Pumps:
EXT255H, EXT255Hi and EXT255HVi
Description Item Number
EXT255Hi/ISO100 B753-03-000
EXT255H/100CF B753-02-000
EXT255H/ISO100 B753-01-000
EXT255HVi/ISO100 B753-07-000

Declaration
ofConformity
We, Edwards,
lvlanorRoyal,
Crawtey,
WestSussex
RH109tW,UK
dectareunderoursole
responsibititythatthe
product(s)
EXTCompound
MolecularPumps:
to whichthisdectarationrelatesisin conformitywith thefottowingstandard(s)
orothernormativedocumentls):
EN1SO12100-2:2003 Safetyof machinery.Basicconcepts,
generalprincipals
for design.
Technicat
principats.
safetyrequirementsforetectricalequipmentfor measurement,
EXT?55H/tSO100
Dff255H/100CF
DCrz55Hi/lSO100
D(T255H/|SO100Portvariant
Dff2551-tui
(Long)
EN61010-1:2001
8753-01-000
8753-m-000
B75r
.03
{00/8753-04-000
8753.06-0m/8753-08-000
8753
-07-000
Controlandlaboratoryuse,Generalrequirements.*
Etl1O1z-Zt1997 Compressor:andvacuum
pumps.
Safetyrequirements.Vacuum
pumps.
EN6'l3Z6t19971 Electricalequipmentfor measurement,
conttolandlaboratoryuse.
+A1
: 1998
+
M: 200'l EMCrequirements.
(lndustriat
Location,
ctassBEmissions)
" The
pumps
complywithEN61010-1
(2001)
wheninstaltedinaccordancewiththe
manual
supptiedwiththe
pumps.
t EN6'1326lmmunity
ctassificationis depeldentonthecontrotler
(see
thecontrotlermanual
for detaits).
fottowingtheprovisions
of:
20061951EC lowVoltageDirective.
Z00/.IIOB|EC ElectromagneticCompatbilityDirective.
98137IEC MachinerySafetyDirective.
furrie Brewster,
TechnicalMandger
- BurgessHill Products
2--tlt- C).k,{u>.. Z.a:<>-T
-EJ@7-61'r-
Date ondPlace
This
producthosbeenmanufqctured
under
dqualitysystemregistered
tolsogffi1
r?owa,Frtr =

© Edwards Limited 2008. All rights reserved. Page i
Edwards and the Edwards logo are trademarks of Edwards Limited.
Contents
B753-03-880 Issue F
Contents
Section Page
1 Introduction .......................................................................................1
1.1 Scope and definitions ................................................................................................... 1
1.2 General description ..................................................................................................... 2
1.3 Vent options and vent control ......................................................................................... 3
2 Technical data ....................................................................................7
2.1 General .................................................................................................................... 7
2.2 Pumping media ........................................................................................................... 7
2.2.1 Pumps without gas purge ............................................................................................... 7
2.2.2 Pumps with gas purge ................................................................................................... 8
2.3 Vent gas specification and vent control data ....................................................................... 8
2.4 Purge gas specification ................................................................................................. 8
2.5 Cooling-water ............................................................................................................ 9
2.6 Materials exposed to gases pumped .................................................................................11
3 Installation ....................................................................................... 15
3.1 Unpack and inspect .....................................................................................................15
3.2 Typical installation .....................................................................................................15
3.3 Connect to the vacuum system .......................................................................................18
3.3.1 Inlet screen ..............................................................................................................18
3.3.2 Mechanical fixing .......................................................................................................18
3.3.3 Base mounting ...........................................................................................................19
3.3.4 Inlet connection and orientation .....................................................................................19
3.3.5 Backing connection .....................................................................................................20
3.3.6 Interstage connection (EXT255Hi/EXT255HVi only) ...............................................................20
3.4 Vent-valve connection and control ..................................................................................20
3.5 Purge gas connection ...................................................................................................21
3.5.1 Connect the purge gas .................................................................................................21
3.5.2 Recommended purge gas flow ........................................................................................21
3.6 Electrical installation ..................................................................................................21
3.7 Cooling ...................................................................................................................21
3.7.1 Introduction .............................................................................................................21
3.7.2 Forced-air cooling ......................................................................................................22
3.7.3 Water-cooling ...........................................................................................................22
4 Operation ........................................................................................ 23
4.1 Start-up ..................................................................................................................23
4.2 Stand-by ..................................................................................................................23
4.3 Shut-down ................................................................................................................24
4.4 Safety interlocks and control system ................................................................................24
4.5 Bakeout ...................................................................................................................24
5 Maintenance ..................................................................................... 27
5.1 Introduction .............................................................................................................27
5.2 Bearing life ..............................................................................................................27
5.3 Rotor life .................................................................................................................27
5.4 Clean the pump .........................................................................................................27
5.5 Fault finding .............................................................................................................28
ITR 22302

B753-03-880 Issue F
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Edwards and the Edwards logo are trademarks of Edwards Limited.
Contents
6 Storage and disposal ........................................................................... 31
6.1 Storage ...................................................................................................................31
6.2 Disposal ...................................................................................................................31
7 Service, spares and accessories .............................................................. 33
7.1 Introduction .............................................................................................................33
7.2 Service ....................................................................................................................33
7.3 Spares .....................................................................................................................33
7.3.1 ISX inlet-screen .........................................................................................................33
7.3.2 Inlet-strainer (EXT255Hi pump only) .................................................................................33
7.3.3 Interstage-port seal (EXT255HVi pump only) .......................................................................34
7.3.4 WCX water-cooler ......................................................................................................34
7.3.5 Inlet-flange seals ........................................................................................................34
7.4 Accessories ...............................................................................................................34
7.4.1 Installation ...............................................................................................................34
7.4.2 EXC controller ...........................................................................................................34
7.4.3 Pump-to-controller cable ..............................................................................................34
7.4.4 EXDC drive modules ....................................................................................................35
7.4.5 BX bakeout band ........................................................................................................35
7.4.6 FL20K foreline trap .....................................................................................................35
7.4.7 TAV vent-valve and vent-port adaptor ..............................................................................37
7.4.8 ACX air-cooler ...........................................................................................................37
7.4.9 Vibration isolators ......................................................................................................37
7.4.10 PRX purge-restrictor ....................................................................................................37
7.4.11 VRX vent-restrictor .....................................................................................................37
For return of equipment, complete the HS Forms at the end of this manual.
Illustrations
Figure Page
1 Cross-section view of EXT255H pump ................................................................................. 4
2 Cross-section view of EXT255HVi pump .............................................................................. 5
3 Maximum allowed rise in backing pressure against time for controlled venting:
system pressure (mbar/Pa) against time (s) ......................................................................... 9
4 EXT255H/EXT255Hi dimensions (mm) ...............................................................................12
5 EXT255HVi dimensions (mm) ..........................................................................................13
6 Typical pumping system with an EXT255H pump ..................................................................16
7 Typical pumping system with an EXT255Hi/EXT255HVi pump ...................................................17
8 Correct installation of the inlet-screen ............................................................................18
9 Installation of optional accessories (and spares): EXT255Hi shown .............................................36
Tables
Table Page
1 Technical data ........................................................................................................... 9
2 Checklist of items .......................................................................................................15
3 Vent-restrictor orifice diameter (with atmospheric pressure at the inlet of the vent-valve) ..............20
4 Fault finding .............................................................................................................28

© Edwards Limited 2008. All rights reserved. Page iii
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Contents
B753-03-880 Issue F
Associated publications
Publication title Publication number
EXC Turbomolecular Pump Controllers: EXC100E and EXC100L D396-20-880
E2M0.7 Rotary Pump A371-31-880
RV Rotary Vane Pumps A652-01-880

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B753-03-880 Issue F
Page iv © Edwards Limited 2008. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.

© Edwards Limited 2008. All rights reserved. Page 1
Edwards and the Edwards logo are trademarks of Edwards Limited.
Introduction
B753-03-880 Issue F
1Introduction
1.1 Scope and definitions
This manual provides installation, operation and maintenance instructions for the Edwards EXT255H, EXT255Hi and
EXT255HVi Compound Molecular Pumps. You must use the Pumps as specified in this manual.
The EXT Compound Molecular Pumps are designed for use with an Edwards EXC Controller. Read this manual and the
instruction manual supplied with your EXC Controller before you attempt to install or operate the equipment. The
EXC Controller contains details of how to set up a pumping system and how to control accessories such as an air-
cooler, vent-valve and bakeout band.
Important safety information in this manual is highlighted as WARNING and CAUTION instructions; you must obey
these instructions. The use of WARNINGS and CAUTIONS is defined below.
CAUTION
Cautions are given where failure to observe the instruction could result in damage to the equipment, associated
equipment and process
In accordance with the recommendations of EN61010, the following warning symbols may appear on the pump or its
accessories:
The units used throughout this manual conform to the SI international system of units of measurement. Also
throughout this manual, wherever flow rates are specified, the abbreviation 'sccm' is used to mean 'standard
cm3min-1: this is a flow of 1 cm3min-1 at an ambient temperature of 0 °C and a pressure of 1013 mbar
(1.013 x 105Pa).
WARNING
Warnings are given where failure to observe the instruction could result in injury or death to
people.
Warning - refer to accompanying documentation.
Warning - risk of electric shock.
Warning - hot surfaces.
Protective conducter terminal.

B753-03-880 Issue F
Page 2 © Edwards Limited 2008. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Introduction
1.2 General description
The EXT255H, EXT255Hi and EXT255HVi pumps are compound vacuum pumps that combine a turbomolecular pump
and a drag pump on a single shaft. Refer to Figure 1 and 2, which show the internal structures of the EXT255H and
EXT255HVi pumps.
The turbomolecular pump is made from a multi-stage axial-flow turbine which is optimised for operation in molecular
flow conditions. The drag pump is made from pumping channels formed by helical grooves. The drag pump is designed
for operation at higher pressures than conventional turbomolecular pumps.
The light alloy rotor (13) is machined from one piece to form the angled blades of the turbomolecular pump. The
rotor blades rotate between angled stator blades (12) which are supported by spacer rings (11). The rotor and stator
blades have an open structure at the pump inlet, and a more closed structure at the outlet. This configuration gives
an optimum combination of pumping speed and compression when pumping gases of both high and low molecular
weight. For the blades to be effective, their speed must be close to the thermal velocity of the gas. The rotor
therefore rotates at up to 60000 r min-1.
Gas from the inlet is compressed through each of the bladed stages of the turbomolecular pump and transferred to
the drag pump. In the drag pump stages, the gas is further compressed as it is pumped around the channels formed
by the helical grooves.
The rotating assembly is supported at the inlet end by a frictionless magnetic bearing (3) and by a precision ceramic
ball bearing (8) at the outlet end. The ball bearing is lubricated from an oil reservoir and wick mechanism (9).
All of the pumps are supplied with an inlet-screen (2) fitted in the bore of the inlet-flange. The EXT255Hi pumps are
also supplied with an inlet-strainer which fits in the interstage-port. The inlet-screen and inlet-strainer protect the
pump against damage which would be caused by debris which enters the pump. The inlet-screen also protects you
from the sharp blades in the pump.
All of the pumps have a vent-port you can use to vent the pump and your vacuum system to atmospheric pressure.
The vent-port introduces vent gas part way up the pump rotor; this ensures maximum cleanliness. The pump is
supplied with a manual vent-valve fitted to the vent-port. As described in Section 3.4, you can replace the manual
vent-valve with a TAV5 or TAV6 solenoid-operated vent-valve (available as an accessory: see Section 7).
All of the pumps have a purge-port (Figure 4 or 5, item 3) in the motor and bearing housing chamber. In order to
protect the bearing lubricant from the effects of high oxygen concentrations, you can introduce an inert purge gas
through the purge-port. You can fit an optional vent-port adaptor and purge restrictor to the purge-port to control
the flow rate of the purge gas and to filter the gas supply (see Section 7).
The EXT255Hi pump has an interstage-port, between the turbomolecular and drag pump. You can use the interstage-
port to pump a separate chamber of your vacuum system or to back another turbomolecular pump. If the pump
operates with an outlet pressure of less than 5 mbar (500 Pa) and an interstage inlet flow of less than 70 sccm
(1.17 mbar l s-1, 117 Pa l s-1), the vacuum performance at the turbomolecular pump-inlet is independent of the
interstage operating conditions.
The EXT255HVi pump also has an interstage-port (14). The interstage-port is located in the turbomolecular pumping
region of the pump and, together with the higher conductance provided by the larger size interstage-port, enables
higher interstage pumping speeds than the EXT255Hi.
Electrical connection between the EXT and the EXC Controller is by a 19-way connector and a pump-to-controller
cable. The cable is a separate item and is available in a choice of lengths (see Section 7 for details). If you use an
EXC100L controller it is not necessary to buy a separate cable.
The pump may be cooled using air-cooled or water-cooled optional accessories. Refer to Section 3 for guidance on
applications and cooling requirements. Pumps with a Conflat flange are supplied with a water-cooler.
All EXT pumps have thermal sensors to monitor the motor and pump-body temperature.

© Edwards Limited 2008. All rights reserved. Page 3
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Introduction
B753-03-880 Issue F
1.3 Vent options and vent 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 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.
However, if you 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. We therefore recommend that you either limit the vent rate (see Section 2.3), or only open the
vent-valve after the EXT pump speed has fallen to 50% of full rotational speed.
The rate of pressure rise cannot be controlled by the manual vent-valve, so if you use the manual vent-valve, you
must only open the vent-valve after the EXT pump speed has fallen to 50% of full rotational speed.
If you use a TAV5 vent-valve, but you cannot limit the rate of pressure rise, you must only open the vent-valve after
the speed of the EXT pump has fallen to 50% of full rotational speed. If you use the EXC Controller to control your
TAV5 vent-valve, configure the EXC Controller to select this option: refer to Section 3.4 for more information. The
EXC Controller is factory set to vent when the EXT pump is at 50% of full rotational speed after you select Stop.

B753-03-880 Issue F
Page 4 © Edwards Limited 2008. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Introduction
Figure 1 - Cross-section view of EXT255H pump
1. Inlet-flange
2. Inlet-screen
3. Magnetic bearing
4. Safety bearing
5. Envelope
6. Shaft
7. DC motor
8. Ball bearing
9. Oil reservoir
10.Drag stage
11.Spacer ring
12.Stator
13.Rotor

© Edwards Limited 2008. All rights reserved. Page 5
Edwards and the Edwards logo are trademarks of Edwards Limited.
Introduction
B753-03-880 Issue F
Figure 2 - Cross-section view of EXT255HVi pump
1. Inlet-flange
2. Inlet-screen
3. Magnetic bearing
4. Safety bearing
5. Envelope
6. Shaft
7. DC motor
8. Ball bearing
9. Oil reservoir
10.Drag stage
11.Spacer ring
12.Stator
13.Rotor
14.Interstage-port

B753-03-880 Issue F
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© Edwards Limited 2008. All rights reserved. Page 7
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Technical data
B753-03-880 Issue F
2Technicaldata
2.1 General
2.2 Pumping media
CAUTION
Do not use an EXT to pump gases containing more than 20% oxygen unless the pump is gas purged. If you do, the
lubricant will polymerise and the pump will fail prematurely.
Note: Note that concentrations of gases may be modified by the compression of the pump.
2.2.1 Pumps without gas purge
The pumps are designed to pump the following residual gases normally used in high-vacuum systems:
Performance See Table 1
Dimensions See Figure 4 and 5
Maximum inlet-flange temperature 100 °C
Maximum magnetic field 3.5 mT Horizontal field >7mT Vertical field
Installation category EN61010 part 1, Category 1
Pollution degree CAN/CSA, UL, EN61010 part 1
Altitude 2000 m
Humidity 10 to 90% non condensing
Electrical supply 80 V d.c.
Equipment type Fixed equipment, for indoor use only
WARNING
Vent dangerous gases and gas mixtures safely. Do not expose people to these gases.
WARNING
Do not use EXT pumps to pump explosive gas mixtures as the pumps are not suitable for this
purpose.
WARNING
On EXT255Hi and EXT255HVi pumps, gas pumped through the interstage-port will mix with gas
pumped through the pump-inlet. Ensure that the gases will not react or combine to form dangerous
gases and substances.
zAir zCarbon monoxide zNeon zEthane zMethane
zNitrogen zKrypton zArgon zPropane
zCarbon dioxide zHelium zHydrogen zButane

B753-03-880 Issue F
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Technical data
You can use the pumps to pump oxygen and water vapour, subject to the following conditions:
If you wish to pump a gas not in the list above, contact your supplier for advice. If you do not contact your supplier,
you may invalidate the warranty on the pump. The pumps are not suitable for pumping aggressive or corrosive gases.
2.2.2 Pumps with gas purge
When purged with an inert gas, the pumps can be used to pump oxygen in concentrations above 20% by volume.
2.3 Vent gas specification and vent control data
Although the pump may be vented to atmospheric air, high relative humidity of the air may greatly increase the
subsequent pump-down time. To reduce pump-down times you should vent the pump with dry, clean gases.
2.4 Purge gas specification
zOxygen The oxygen concentration must be less than 20% by volume.
zWater vapour You must ensure that vapour does not condense inside the pump; refer to Section 3.7.3.
Vent gas Dry air, nitrogen, argon or other inert gases
Maximum dew point at atmospheric pressure - 22 °C
Maximum size of particulates 1 µm
Maximum concentration of oil 0.1 parts per million
Time for rotational speed to reach 50% >15 sec
Rate of pressure rise see Figure 3
Purge gas Dry nitrogen, argon or other inert gases
Maximum dew point at atmospheric pressure -22 °C
Maximum size of particulates 1 µm
Maximum concentration of oil 0.1 parts per million
Allowable purge gas flow (when required) 20 to 100 sccm (0.33 to 1.67 mbar l s-1, 33 to 167 Pa l s-1)
Recommended purge gas flow 25 sccm (0.42 mbar l s-1, 42 Pa l s-1)
Maximum allowable purge gas supply pressure 2 bar (gauge) ; 29 psig, 3 x 105Pa

© Edwards Limited 2008. All rights reserved. Page 9
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Technical data
B753-03-880 Issue F
Figure 3 - Maximum allowed rise in backing pressure against time for controlled venting:
system pressure (mbar/Pa) against time (s)
2.5 Cooling-water
The following cooling water specification corresponds to a typical high-quality drinking water specification. Check
with your water supply authority if you are in doubt about the quality of your supply.
Quality Mechanically clean and optically clear with no deposits or turbidity.
pH value 6.0 to 8.0
Maximum calcium carbonate concentration 75 parts per million
Maximum chloride concentration 100 parts per million
Minimum oxygen concentration 4 parts per million
Minimum water-cooling flow rate (at 15 °C) 15 l h-1
Water temperature See Table 1
Maximum water pressure 5 bar (gauge), 73.5 psig, 6 x 105Pa
Materials exposed to cooling water Nickel plated brass
Table 1 - Technical data
Parameter EXT255H EXT255Hi EXT255HVi Notes
Mass
DN100ISO-K inlet flange 5.6 kg 5.6 kg 6.5 kg
DN100CF inlet flange 8.2 kg N/A N/A
Inlet-flange DN100ISO-K/
DN100CF DN100ISO-K DN100ISO-K
Outlet-flange DN25NW DN25NW DN25NW
Vent-port 1/8 inch BSP 1/8 inch BSP 1/8 inch BSP
Interstage-port - DN25NW DN40NW
Purge-flange DN10NW*DN10NW*DN10NW*

B753-03-880 Issue F
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Technical data
Inlet pumping speed
N2†‡220 l s-1 220 l s-1 195 l s-1 Pb < 5 mbar (500 Pa)
Qi < 70 sccm
(1.17 mbar l s-1)
(117 Pa l s-1)
He †‡230 l s-1 230 l s-1 155 l s-1 Pb < 1 mbar (100 Pa)
Qi = 0 sccm
H2†‡180 l s-1 180 l s-1 100 l s-1 Pb < 0.5 mbar (50 Pa)
Qi = 0 sccm
Inlet compression ratio
N2†‡> 1 x 108>1 x 1083 x 108Pb < 5 mbar (500 Pa)
He †‡4 x 1052.5 x 1052 x 105Pb < 2 mbar (200 Pa)
H2†‡1.6 x 1041.1 x 1045 x 103Pb < 1 x 10-2 mbar (1 Pa)
Interstage pumping speed ‡
N2†-10ls
-1 21 l s-1 Pb = 5 mbar (500 Pa)
Qi = 240 sccm (4 mbar l s-1)
(400 Pa l s-1)
Qp = 0 sccm
He†-10ls
-1 23 l s-1 Pb = 5 mbar (500 Pa)
Qi = 100 sccm
(1.67 mbar l s-1)(167 Pa l s-1)
Qp=<20 sccm
(0.33 mbar l s-1)(33 Pa l s-1)
Ultimate pressure with rotary
vane backing pump **
DN100ISOK inlet flange < 5 x 10-9 < 5 x 10-9 < 5 x 10-9
DN100CF inlet flange < 5 x 10-10 --
Ultimate pressure with
diaphragm backing pump ††
DN100ISOK inlet flange < 5 x 10-8 < 5 x 10-8 < 5 x 10-8
DN100CF inlet flange < 5 x 10-8 --
Maximum backing pressure ‡‡
N212 mbar
(1200 Pa) 12 mbar (1200 Pa) 12 mbar (1200 Pa)
He 10 mbar
(1000 Pa) 10 mbar (1000 Pa) 10 mbar (1000 Pa)
H23 mbar
(300 Pa) 3 mbar (300 Pa) 3 mbar (300 Pa)
Minimum backing pump
displacement 0.6 m3h-1 0.6 m3h-1 0.6 m3h-1
Maximum continuous inlet
pressure ***
water-cooling at 15 °C *** 2 x 10-1 mbar,
20 Pa 2 x 10-1 mbar, 20 Pa 2 x 10-1 mbar, 20 Pa
air-cooling at 35 °C*** 2 x 10-2 mbar,
2 Pa 2 x 10-2 mbar, 2 Pa 2 x 10-2 mbar, 2 Pa
Table 1 - Technical data (continued)
Parameter EXT255H EXT255Hi EXT255HVi Notes

© Edwards Limited 2008. All rights reserved. Page 11
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Technical data
B753-03-880 Issue F
2.6 Materials exposed to gases pumped
The following materials and component types are exposed to the gases pumped: aluminium alloys, stainless steels,
fluoroelastomer and nitrile 'O' rings, hydrocarbon lubricant, felt, rare earth magnets, silicon nitride, phenolic resin
and carbon-fibre reinforced epoxy resin.
Operating attitude Vertical and upright through to horizontal ±2°
Nominal rotational speed 60000 r min-1 60000 r min-1 60000 r min-1
Standby rotational speed 42000 r min-1 42000 r min-1 42000 r min-1
Starting time to 90% speed
EXC100E 190 sec 190 sec 190 sec
EXC120 130 sec 130 sec 130 sec
EXC300 100 sec 100 sec 100 sec
Cooling method Forced-air/
water Forced-air/ water Forced-air/ water
Ambient air temperature
(forced-air cooling) 0 - 35 °C 0 - 35 °C 0 - 35 °C
Water temperature
(water-cooling) 10 - 20 °C 10 - 20 °C 10 - 20 °C
Noise level (at 1 metre) < 50 dB(A) < 50 dB(A) < 50 dB(A)
Recommended controller EXC120 EXC120 EXC120
EXC120 maximum VA input 250 VA 250 VA 250 VA with bakeout band
Quiescent power 25W 25W 25W
Recommended backing pump ††† RV3 RV3 RV3
*Not supplied - pump supplied with port blanked.
†Pb = backing pressure, Qi = flow through the interstage-port (EXT255Hi/EXT255HVi only), Qp = flow through
pump-inlet.
‡Pumping speeds are without inlet-screen or inlet-strainer (EXT255Hi/EXT255HVi only). Inlet-screens and
inlet-strainers reduce speed by approximately 10%.
** Ultimate pressure 48 hours after bakeout with Pb < 1 x 10-2 mbar (1 Pa).
†† Ultimate pressure 48 hours after bakeout with Pb < 5 mbar (500 Pa).
‡‡ Inlet pressure has risen to 1 x 10-3 mbar (1 x 10-1 Pa).
*** Above this pressure, rotational speed drops below nominal.
††† A larger backing pump may be required for maximum throughput.
Table 1 - Technical data (continued)
Parameter EXT255H EXT255Hi EXT255HVi Notes

B753-03-880 Issue F
Page 12 © Edwards Limited 2008. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Technical data
Figure 4 - EXT255H/EXT255Hi dimensions (mm)
1. Interstage-port (EXT255Hi only)
2. Vent-valve
3. Purge-port
4. Electrical supply connector
5. Backing-port
6. Cooling-water connectors
7. Allowance for right-angle cable connector
8. Earth (ground) bonding point

© Edwards Limited 2008. All rights reserved. Page 13
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Technical data
B753-03-880 Issue F
Figure 5 - EXT255HVi dimensions (mm)
5. Backing-port
6. Cooling-water connectors
7. Allowance for right-angle cable connector
1. Interstage-port
2. Vent-valve
3. Purge-port
4. Electrical supply connector

B753-03-880 Issue F
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