B800-00-880 Issue A
Page 56 © Edwards Limited 2009. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Operation
If the electrical supply to the nEXT pump fails when the pump is rotating, the motor of the pump is used as a
generator. The regenerated power is used to maintain the output signals on the logic interface (such as the Normal
signal and serial communications), to power the three indicator LEDs on the Controller and to maintain power at the
Controller output (to control the vent valve, if fitted).
As the pump rotational speed decreases, the motor's ability to generate power also decreases until it is no longer
able to maintain power to the logic interface or LEDs. This will occur at speeds below 50% full rotational speed.
Therefore you will not have any indication about pump rotational speed, yet the impeller may still be turning.
When the power is reinstated after a power failure, the behaviour of the pump will depend on the control mode at
the time of failure (parallel or serial) and the length of time the pump was without power. Table 24 shows a number
of scenarios.
4.10 Bakeout
Pumps with ISO flanges are not suitable for bakeout, only pumps with CF flanges must be used. When baking the
pump to above 70 °C at the inlet-flange, the pump must be water-cooled to prevent damage to the bearing
lubricant.
If you heat your pump (and your vacuum system), you will speed up the degassing process so that the pump will reach
ultimate vacuum in the shortest possible time. If you heat the pump, this will also prevent condensation of vapours
inside the pump.
The Edwards BX bakeout band may be used to heat the pump (refer to Section 7.4). Fit the appropriate band around
the pump, just below the CF inlet-flange. When baking the pump or the system, make sure that the temperature of
the inlet-flange does not exceed the values specified in Table 2.
When baking your vacuum system, if the temperature of the system exceeds 200 °C, you must put a radiation shield
between the system and the pump. This radiation shield will reduce the heat radiated onto the pump rotor.
Typically, a bakeout of four hours is long enough to remove water condensation from the pump. However, the
bakeout time will depend on the amount of condensation in the pump and the vacuum system, and the ultimate
pressure you want to achieve.
Do not touch the bakeout band or surrounding surfaces during the bakeout process as they will be
hot.
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