Pressure limitation method

The pressure in a glovebox is maintained, for safety, between predetermined negative and positive limits relative to atmospheric pressure by means of a lute comprising a closed vessel having a tube sealed through its upper region and extending downwards towards its lower region and having an open end thereat. The other end of the tube is connected to the glovebox and the upper region of the vessel is vented to atmosphere via an extract system. The vessel and tube are filled with liquid to such a level, sealing the open end of the tube, that (a) at the said negative limit the liquid level in the vessel falls to unseal the tube and allow atmospheric air to enter the glovebox, and (b) at the said positive limit the liquid level in the tube falls to unseal the tube and allow gas from the glovebox to vent to atmosphere. A catch-pot is provided between tube and the glovebox to prevent any entrained liquid entering the glovebox, and similar means may also be provided to prevent any entrained liquid entering the extract system. (author)