B722-20-880 Issue D
Page 26 © Edwards Limited 2008. All rights reserved.
Edwards and the Edwards logo are trademarks of Edwards Limited.
Operation
4.3 Shut-down due to pump under or over-speed
The EXDC Drive Module monitors the temperature of the EXT pump and the electrical power consumption of the
pump. If the EXDC Drive Module detects excessive power consumption or temperature, the rotational speed of the
pump motor is reduced until the power and temperature return to normal.
Shut down the EXT pump if its speed falls below 50% of full rotational speed. If you do not, the EXT pump may
be damaged.
If the pump speed is reduced to 50% of nominal speed this means that the inlet pressure or pump temperature are
too high, or that there is a fault with the pump (for example, the bearings may have failed). If the pump speed falls
to below 50% of its full rotational speed you must therefore switch the pump off. Instructions on how to monitor pump
speed can be found in the EXDC drive module manual.
The EXDC has an electronic EXT pump speed control system. This control system prevents operation of the EXT pump
at over 100% of its normal full rotational speed (as operation above this level reduces bearing operational life). In
the unlikely event of a failure of this control circuit the pump may overspeed. If you suspect that your pump may be
running at overspeed you should switch it off and consult Edwards or your supplier.
4.4 Bakeout
When baking the EXT 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 EXT 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). Fit the band around the pump, just
below the inlet-flange. When baking the pump or the system, make sure that the temperature of the inlet-flange
does not exceed 100 °C.
When baking vacuum system, if the temperature of the system exceeds 200 °C, you must put a radiation shield
between the system and the EXT 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.
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