ABB HPA 12kV Instruction For Installation, Service And Maintenance page 6

During the manufacture of the breaker pole, it is dried internally through vacuum
pumping. The breaker pole is then pressurized and also tested against leaks. Inside
the pole there is an absorption medium for the decomposition products of the gas. The
breaker poles should only be opened up by trained service personnel at the
manufacturing factory. The locking screws are tightened up to a predetermined
torque at the factory and must not be opened. If it is assumed that moisture has
entered (gas pressure = atmospheric 0) the pole, the same should be returned to the
factory for repair.
SF gas which has been exposed to arcs contain components which combined with
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moisture become corrosive. Filling up of gas should always be carried out according
to section 2.3.2 "Checking and Refilling of Sf gas".
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Fig - 3a
(HPA breaker pole for 12 kV / 24 kV)
(5)