Cryopumps are gas entrapment vacuum pumps for the pressure range from
10-3 to < 10-11 mbar (0.75 x 10-3 to ≤ 0.75 x 10-11 Torr). The
principle of operation is that gaseous substances are bound to the
cold surfaces within the pump by means of cryocondensation,
cryosorption or cryotrapping.
In order to be able to produce a high or ultra high vacuum the cold
surfaces (cryopanels) must be cooled to a sufficiently low
temperature. Depending on the type of cooling system used a
difference is made between refrigerator cryopumps, bath cryopumps
and evaporator cryopumps. Leybold manufactures only cryopumps
which are cooled by means of a refrigerator.
Advantages to the User
Advantages offered by the Pumping Principle
High effective pumping speed for all gases
Extremely high pumping speed for water vapor
For a given diameter of the high vacuum flange, the
cryopump offers the highest pumping speed of all high vacuum pumps.
Advantages offered by Design
In contrast to gas transfer high vacuum pumps (mechanically
suspended turbomolecular pumps, for example), cryopumps do not have
any mechanically moving, oil, or grease lubricated parts on the
vacuum side.
The following advantages are a direct result of this design
characteristic:
Hydrocarbon-free vacuum in the pressure range
from 10-3 to < 10-11 mbar (0.75 x 10-3 to ≤ 0.75 x 10-11 Torr).
Insensitivity to mechanical disturbances from
particles coming from the process or external vibrations.
Further Advantages
Much more compact than comparable pump systems
offering a pumping speed of over
1500 l x s-1
Backing pump is only required during start-up
and during regeneration
Easy process control and pump control via
computer
Favourable price-to-performance ratio and low
running costs especially at higher pumping speeds
The cryopumps are cooled by the well-proven
two-stage cold heads from Leybold’s COOLPOWER line (Gifford/McMahon
principle). The design of a refrigerator cryopump from the
COOLVAC range is shown schematically in the figure below.
The first stage of the cold head (9) cools the thermal radiation
shield (5) and the baffle (6) of the pump. Depending on the
type of pump and the operating conditions operating temperatures of
45 to 80 K are attained. Correspondingly water vapor condenses
at this temperature.
The thermal shield and baffle are made of copper
which conducts heat very well so as to optimally utilize the
refrigerating capacity which is available.
Moreover, the thermal shield is metallized so that reflective losses
will be minimal.
The second stage of the cold head (7) is used to cool the cryopanels
(8). Depending on the operating conditions, operating
temperatures of 10 to 20 K are attained. Here the process of
cryocondensation of N2, O2 and argon will take place.
The active pumping surfaces are made of copper of high thermal
conductivity and they are tightly linked thermally to the second
stage of the cold head. H2, Ne and He are also adsorbed on to these
surfaces which are partly covered with activated charcoal.
All cryopumps from the COOLVAC range are equipped with a safety valve
(respectively with a bursting disk in the case of the UHV variants)
which is set in the factory so that it will open at an overpressure
of 150 mbar (113 Torr). In order to be able to safely remove any
gases
which may present a health hazard when the safety valve responds,
the valve is equipped with an additional DN 40 KF flange where an
exhaust line is connected. The pump’s body, all flanges and
the safety valve are made of high-quality stainless steel.
Upon request we will be pleased to mail you our special publication
SO 182.04.02 “Benefits of modern refrigerator cryopumps in
industrial processes and research”.
Multiple Operation of Refrigerator Cryopumps
The powerful Leybold compressor units COOLPAK 4000 D and 6000 D open
up the possibility of operating two cold heads or refrigerator
cryopumps simultaneously.
Advantages to the User
Significantly reduced investment and operating costs
Small footprint
Regenerating Cryopumps
An important aspect in the operation of cryopumps is that of
regeneration. Since a cryopump is a gas entrapment pump, the
gasses which have accumulated in the pump during the “pumping” mode
must from time to time be removed from the pump. This is done
by switching the compressor unit off and by warming up the
cryopanels to room temperature or sightly higher so that the
released substances can be pumped out by a forevacuum pump.
Cryopumps without Electric Regeneration System
The cryopump is warmed up to room temperature by purging the inside
of the pump with a dry, pre-warmed inert gas (such as nitrogen). In
this case it is not possible to set up defined and controlled
temperatures within the cryopump. Thus the simultaneous presence of
gases such as hydrogen and oxygen in the pump can not be entirely
excluded. The formation of ignitable gas mixtures is only prevented
by the diluting effect of the dry inert gas.
Cryopumps with Fully Automatic Electric Regeneration System from
Leybold
The cryopump is warmed up to room temperature by heating the 1st and
2nd stages of the cold head with electric heaters. In this case, a
defined and controlled temperature distribution within the cryopump
can be set up. This controlled warming process ensures that the
pumped
gases are removed sequentially, i.e. the pumped gases are released
one after the other in the following sequence:
Gases adsorbed at the cryopanels (e.g. hydrogen, helium,
neon),
Gases condensed at the cryopanels (e.g. nitrogen,
oxygen, argon),
Gases and vapors which have condensed on to the baffle
and thermal radiation shield (e.g. water vapor).
The electric method of regeneration from Leybold prevents gases such
as hydrogen and oxygen from being present in the pump at the same
time. This excludes the formation of
ignitable gas mixtures right from the start.
Cryopumps without fully automatic control and without electric
regeneration system belong to the BasicLine (BL), like the COOLVAC
800 BL, for example.
The warming up process is fully automatic. Pressure and temperature
distribution within the pump are set up and controlled by the
control system at all times. The sequential regeneration of pumped
gases prevents the formation of ignitable gases right from the
start. This ensures the utmost safety during the regeneration of
cryopumps from Leybold.
In the case of cryogenic pumps with fully automatic control there
exist two cryo pump lines.
1. The COOLVAC BasicLine (COOLVAC BL) offering the following pumping
speed class for Nitrogen in l/s: 800; COOLVAC 800 BL, for example.
Other pumping speed classes from 1 500 to 18 000 l/s are available
on request. For more information please contact your local
Leybold Vacuum representative.
2. The COOLVAC ClassicLine (COOLVAC CL) offering the following
pumping speed classes for
nitrogen in l/s: 800, 1 500, 2 000, 3 000, 5 000, 10 000 and 18 000;
COOLVAC 1500 CL, for example.
In the price list the designators “V” appears in connection with the
pump designations.
“V”:
The high-vacuum flange is located at the top and the cold head
below, as is the case for the COOLVAC 1500 CL-V, DN 200 CF.
Leybold Vacuum Full Line Catalog 2005
For a PDF file of this product please contact us here.
file.
