GB1146778A - Fume cupboards for chemical laboratories - Google Patents

Abstract

1,146,778. Fume cupboards. H. KRANTZ VERWALTUNGS G.m.b.H. 22 March, 1967, No. 13554/67. Heading F4X. A fume cupboard comprises a cabinet which incorporates a work-table 1, an opening 5 at the front closable by a slidable sash window 4, an exhaust duct 2 adjacent the back wall, and an inlet opening 11 in the top adjacent the sash window, so arranged that fresh air entering through the inlet 11 is deflected into the interior of the fume cupboard by a baffle 8 on the bottom edge of the sash window, and along with air that enters through the opening 5 ventilates the cupboard before extraction therefrom through the duct 2. The inlet opening 11 is shown in the form of a convergent-divergent Venturi duct extending across the full width of the window, thus causing the entering fresh air, when deflected by the baffles 8 to form a revolving barrel-shaped vortex 9 in the upper part of the fume cupboard, thereby separating the window opening 5 from the air motions in the upper part of the cupboard interior 3. The volume of inflowing fresh air is determined by the relatively low pressure inside the fume cupboard and by the cross-section of the exhaust. To remove the vapour-charged exhaust gas through the exhaust duct 2 as quickly as possible, discharge slots 16 in the form of Borda mouthpieces are arranged along the top, back and side walls. In another embodiment (see Fig. 3), the volume of fresh air admitted is not determined by the sub-atmospheric pressure inside the fume cupboard, but is forced through by a fan, due care being taken that the inflowing air is only a portion of the outflowing exhaust, and is such that air entering through the opening 5 to make up the difference has a sufficiently high entry velocity to prevent polluted air from forcing its way out of the cabinet.