A major construction equipment manufacturer wished to replace its outdated sodium silicate-type of impregnation system. They opted to have the equipment built so that either a vacuum-only or a vacuum-pressure process utilizing imprex resin could be used. Experience has shown that vacuum only will achieve about the same results as vacuum pressure except in instances where certain high-pressure gases (such as freons) must be contained.
Because of the extremely minute leakage rates sometimes involved ( less than one cc leakage per hour at 250 psig) a vacuum-pressure system is the only type of equipment available that will successfully seal such porosity.
Note that this type of unit has but half the production capacity of a conventional vacuum-only system because the process entails ( 1 ) a dry vacuum cycle, ( 2 ) transfer of resin to the chamber, ( 3 ) a pressure cycle and (4 ) return of resin to the reservoir.
