B064-04-880 Issue F
Page 4
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Introduction
1.3
Principle of operation
Pump fluid is heated in the base of the pump to produce a vapour which passes up through the interior of the jet-
stages and emerges from the jets as high-velocity vapour streams. The vapour streams condense on the cooled walls
of the jet-stage cone and the ejector-stage cones and drain into the base of the pump for recirculation.
A portion of system gas which arrives at the pump-inlet is trapped in the vapour stream from the first jet-stage. The
gases are compressed and transferred to the next stage. The gases then pass through the two ejector-stages and into
the backing-condenser where they are removed by the backing-pump.
The cooled surface of the guard-ring above the first jet-stage traps and condenses pump fluid vapour and minimises
any back-streaming of pump fluid vapour into the vacuum system.
1.4
Over-temperature protection
Note:
The following sections describe the operation of the snap-switches on control configured pumps; you must
ensure that unconfigured pumps will operate in the same way: refer to
.
1.4.1
Cooling-fail thermal snap-switches
. The pump has three cooling-fail thermal snap-switches (7) on the cooling-coils. These snap-
switches are connected to the control-box (11). The snap-switches protect the pump against damage due to failure
of the cooling-water supply. If the temperature of the pump increases above 46 °C, the snap-switches will operate
to switch off the pump heaters. The snap-switches will reset automatically when the pump cools down.
The operating temperatures of the cooling-fail thermal snap-switches are preset for use with AP201 pump fluid. If
you want to use other fluid types in the pump, contact your supplier or Edwards for advice.
1.4.2
Boiler protection thermal snap-switches
. The pump has two boiler protection thermal snap-switches (12). One snap-switch is fitted to the
fluid return-tube (8) from the backing-condenser, and the other snap-switch is fitted next to the drain plug (21).
These snap-switches are also connected to the control-box (11). The snap-switches protect the pump against damage
due to a low level of pump fluid. As supplied, the snap-switches will operate at 250 °C to switch off the heaters. You
can adjust the snap-switches to operate at different temperatures (refer to
1.5
Full-heat and half-heat modes (control configured pumps only)
Control configured pumps have two operating modes: full-heat and half-heat. You can select these modes with the
Heater Power switch on the control-box (see
The full-heat mode is the normal operating mode. When this mode is selected, all the heaters are switched on.
When the half-heat mode is selected, the electrical supply to some of the heaters is switched off. If you have a cyclic
process, you can select this facility when the 30B5M is not used to pump process gases; this will reduce the power
consumption of the pump, but also maintain the pump close to its operating temperature.
WARNING
Ensure that the boiler protection thermal snap-switches are wired into the pump control system,
and are correctly adjusted when the pump is fully charged with fluid and under vacuum.
The thermal trips are to protect the pump from overheating from low oil level, which may cause
the boiler to implode.