Description; Design And Function - Edwards nHT10 Instruction Manual

3. Description

The pumps in the nHT series are high vacuum pumps (< 10
operated together with the backing pumps.
The pumps are water cooled and utilise the oil diffusion principle in their operation.
They are used in high vacuum technology to evacuate vacuum chambers.
The pumps achieve the highest pumping speeds in pressure ranges from 10
-7
10 mbar.

3.1 Design and function

The pumps comprise the following component assemblies:
▪ A water cooled pump housing with inlet and outlet vacuum connection flanges
▪ An interior assembly
▪ An internal vaporisation chamber (boiler) with heating elements
▪ A water cooled cold cap baffle
▪ A backing baffle
▪ An electrical terminal box.
Interior assembly
The pumps are fitted with a five-stage precision interior assembly. It consists of four
diffusion jet stages and an ejector stage, made of light alloy metal.
Pump body
The pump body is made of standard grade steel. The inlet connection flange and the
outlet vacuum flange are made of stainless steel. The external cooling coils are made of
copper.
Heat diffusion fins
The external coiled heating fins on the cartridge heaters are made of stainless steel and
are immersed for the most part in the pump fluid in the vaporisation chamber.
The section of the heating fin immersed in the pump fluid produces intense but surge
free vaporisation of the pump fluid.
The section of the heating fin located above the level of the pump fluid applies
additional energy to the pumping vapour.
Thermostat
To protect the heating element, a thermostat sensor is attached to one of the heater
cartridges. When installed, it protrudes above the fluid. It must be used to turn off the
pumps heaters as soon as the bimetallic switch temperature reaches the preset trip
point.
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mbar). They are always
-2
to
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