Implosion proof desiccators. Will take vacuum of -740 mm Hg with loss (absolut zero: -760 mm/HG) not exceeding 20 mm Hg in 24 hours. The transparent polycarbonate cover seals onto a neoprene '0' ring set into the flange of the PP base. A little grease spread on the '0' ring will assist in establishing initial vacuum. Within the desiccator is a removable pan for holding a drying agent. Vacuum release tap/non return valve assembly is included; specially grooved stopper in this assembly allows air, when required, to be re-admitted very slowly to avoid disturbing the contents.rrThe discs (or plates) are not incorporated and must be ordered separately.