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B348-00-880 Issue J
1.2
Description
The Mk 2 series of Cryo-Cooled Diffstaks are compact high-performance diffusion pumps which provide exceptionally
clean pumping and minimum pump-down times, even when high vapour loads are pumped.
The basic Cryo-Cooled Diffstak consists of a diffusion pump, a cryo-cooled disk, a water-cooled baffle, a high-vacuum
isolation-valve and a roughing connection all integrated into a water-cooled stainless steel casing. The high-vacuum
isolation-valve is part of the inlet-flange and is configured for either manual or pneumatic operation:
M-model pumps have a manually-operated high-vacuum isolation-valve.
P-model pumps have a pneumatically-actuated high-vacuum isolation-valve.
Pneumatic high-vacuum isolation-valves have position indicators which indicate whether the valve is open or closed.
You can connect the position indicators to your control or indicator equipment.
Four sizes of pumps are available with either a 63 mm, 100 mm, 160 mm or 250 mm diameter inlet-flange. The largest
pump has a pumping speed of up to 1700 l s
1.3
Construction
The Cryo-cooled Diffstak is a three-stage fully fractionating diffusion pump with an ejector-type third-stage. The
pump-body is water-cooled and made of stainless steel with a mild-steel nickel-plated base.
The inlet-flange has an integral roughing pipeline, to which an Edwards BRV combined backing/roughing-valve can
be connected in the Diffstak CR63/150, CR100/300 and CR160/700 pumps. The Diffstak CR250/2000 is designed to
use separate roughing and backing pipeline-valves. You can fit a vacuum gauge head to the flange provided on the
roughing pipeline of all pumps. Housed within the inlet-flange is the low-impedance high-vacuum isolation butterfly-
valve. A sectional view of the Cryo-Cooled Diffstak pump is shown in
A liquid-nitrogen cooled (high-conductance) disk is located below the valve. The surfaces of the disk are attached to
a copper probe which is cooled by conduction to the reservoir of liquid nitrogen. The stainless steel reservoir
connects to the body of the pump through a flanged tube and the vacuum around the reservoir is common with the
vacuum at the pump-inlet. A copper fin extends downwards inside the reservoir to ensure a small temperature
gradient, even with a low level of liquid nitrogen inside the reservoir.
A baffle is located below the cryo-cooled disk. The baffle consists of a water-cooled flanged cylinder with a
detachable cover. The baffle also retains the jet assembly by spring pressure.
The interior jet system consists of a first, second and third-stage jet assembly with fractionating tubes. Above the
jet system is a detachable first-stage jet-cap. The jet system is clamped together by a central tie-rod.
The boiler is located in the base of the pump. The pump fluid is heated and vaporised by plate-type electric heater(s)
(one or two, this depends upon the size of the Diffstak). The boiler has a fluid filler connection and a drain-plug. The
electrical supply cables from the heater are brought out to a terminal-box at the bottom of the pump for ease of
connection to your electrical supply.
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Edwards and the Edwards logo are trademarks of Edwards Limited.
1.
© Edwards Limited 2008. All rights reserved.
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