b35033977 - Unvalved Diffstak 250/2000C Vapor Pump, 210-225 V, 1Ø, 50/60 Hz

Unvalved Diffstak 250/2000C Vapor Pump, 210-225 V, 1Ø, 50/60 Hz



The compact water-cooled Diffstak pumps with an integral cooled baffle offer exceptionally clean pumping with very low backstreaming, reduced outgassing, and a reduction in the number of elastomer seals required for installation.

The Edwards Diffstak 250 (ISO250 inlet) design has been proven over many years with thousands of pumps installed.

This pump has an unvalved ISO collar inlet flange and is supplied with: NW40 elbow, NW40 centering-ring, NW40 clamp, water pipe couplings and ferrules, inlet ISO 250 trapped ‘O’ ring.


The 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 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 vaporized by plate-type electric heater(s) (one or two, this depends on 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.
Principle of Operation
Pump fluid is heated in the boiler to produce a vapor which passes up through the interior of the jet assembly and emerges from the jets as high-velocity Vapour streams. The vapor streams condense on the cooled pump-body wall and drain into the boiler at the bottom of the pump for recirculation.
A portion of system gas which arrives at the Diffstak pump-inlet is trapped in the vapor stream from the first-stage jet. The gases are compressed and transferred to the next stage. This process is repeated through the pump jet-stages until the gases are removed by the backing pump through the cooled backing-condenser.
The fractionating feature of the Diffstak design provides a means of purging the fluid charge of undesirable light fractions and foreign matter and the process helps significantly towards the attainment of a low ultimate vacuum.
The ejector jet also purges the fluid of any contaminants as it returns to the boiler and at the same time ensures a high critical backing pressure even when you use low vapor pressure fluids.

Technical Data

Pumping speed
nitrogen 2130 l s-1
hydrogen 3200 l s-1
Min backing pump displacement* 40 m3h-1
Recommended backing pump E2M40
Recommended fluid Santovac® 5
Fluid charge (dry) 500 ml
Inlet connection compatible with ISO250
Backing connection NW40
Cooling water connection 10 mm compression fittings
Heater power 2.25 kW
Min cooling-water flow at 20°C 180 l h-1
Weight 46 kg

* For maximum throughput



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