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Page 17
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Installation
B777-00-880 Issue E
3.7
Cooling
3.7.1
Introduction
CAUTION
You must cool the pump by forced-air or water cooling to prevent damage to the bearing.
You must use water cooling in any of the following operating conditions:
z
When backing pressure is high (see
z
When you bake the EXT pump or the vacuum system close to the pump.
z
When the ambient temperature is above 35 °C.
z
When there is high continuous gas throughput (see
).
In all other operating conditions, you can use forced air cooling. If you use forced air cooling you must ensure that
there is an adequate supply of cooling air to the pump.
3.7.2
Forced air cooling
An air cooler accessory is available for the EXT555H pump (see
). Fit the air cooler as described in the
instructions supplied with it. If you wish to use alternative air cooling, ensure that the flow rate is above 280 m
3
h
-1
(80 l s
-1
, 160 cfm).
3.7.3
Water cooling
A water cooling accessory is available for the EXT555H pump (see
). Fit the water cooler as described in the
instructions supplied with it. It is not necessary to use thermal transfer paste with this water cooling accessory.
CAUTION
To prevent excessive thermal gradients from developing across the bearing, do not use thermal transfer paste
between the water-cooling accessory and the turbo-pump body.
CAUTION
Whilst pumping gases with rmm’s >28amu, or in the event that you are required to bake the pump, then you
must ensure that you limit the inlet and backing pressure according to the values given in
The cooling water must comply with the specification given in
. Pipes in the water cooling circuit may
become blocked if the cooling water contains too much calcium carbonate or if it contains particulates which are too
large. Corrosion of the water cooling circuit may occur if there is too little calcium carbonate or oxygen in the water.
Good quality drinking water is usually suitable for water cooling. If in doubt you must check the quality of your cooling
water supply and, if necessary, provide treatment and filtration.