B722-01-880 Issue K
Page 2
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Introduction
1.2
Description
The EXT turbomolecular pumps are multi-stage axial-flow turbines, optimised for operation in molecular flow
conditions. The internal structures of the EXT70 and EXT250 Turbomolecular Pumps are shown in
and
.
The multi-stage, light alloy turbine rotor (12) is machined from one piece to form rows of angled blades fitted to a
central shaft (6). The blades of the rotor rotate between the blades of the stator. The stator assembly (11) is a series
of thin disks separated by spacer rings (10). The blades are angled so that the gas in the vacuum chamber is
compressed and is transferred from the pump-inlet to the outlet.
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 the pump is operated with
gases of both high and low molecular weight.
The rotor is driven by a high-efficiency, brushless d.c. motor. The motor (7) has a magnetized rotor fitted onto the
shaft, and a wound stator located in the pump-body. For the blades to be effective, their speed must be close to the
thermal velocity of the gas molecules. The rotor is therefore rotated at up to 90000 r min
-1
.
The rotor assembly is supported at the inlet end by a frictionless magnetic bearing (3) and by a precision ball bearing
(8) at the outlet end. The ball bearing is lubricated from an oil reservoir and wick mechanism (9).
EXT pumps are supplied with an inlet-screen (2) fitted in the bore of the inlet-flange. The inlet-screen protects you
from the sharp blades and also protects the pump against damage caused by debris which falls into the pump.
EXT pumps have a vent-port which 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 to ensure maximum cleanliness even with
fluoroelastomer sealed vent-valves. The pump is supplied with a manual vent-valve fitted to the vent-port. As
described in
, you can replace the manual vent-valve with a TAV5 solenoid-operated vent-valve (available
as an accessory: see
).
The EXT250 pump has a purge-port (
, item 1) in the motor and bearing housing chamber. You can introduce
an inert purge gas through the purge-port to protect the bearing lubricant from the effects of high oxygen
concentrations. You can fit an optional purge restrictor to the purge-port to control the flow rate of the purge gas
and to filter the gas supply (see
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
for details).
The pump may be cooled using air-cooled or water-cooled optional accessories and the EXT70 may also be cooled by
natural convection to the surrounding air. Refer to
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.
Содержание EXT250 Series
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