Vacuum Box Testing Equipment
www.vacuumboxtesting.com An efficient method for leak testing welds is using a vacuum box to pull negative pressure on one side while then looking for bubbles through a soap solution. The test is performed by one person. The vacuum box is a clear Plexiglas plate with soft gasketing around the edges. The vacuum is pulled by using a standard shop air connection hooked up to a venturi nozzle. The air blowing through the venturi creates a low pressure area through the restriction; a port at this point pulls the air out of the Plexiglas box. The vacuum in the box will pull down as low as 22″Hg or 112″WC, the equivalent of 11 psig positive pressure on the opposite side of the weld. This is an ideal test for low pressure ducting that is often rated in inches of water column service but where an 11 psig test would be an excessive loading otherwise. Commonly, such fabricated ducting would be tested with a method referred to as ‘soap and air’. A soap and air test is performed by one person blowing an air hose on one side of the weld while the QC person sprays a soap solution on the other side and checks for bubbles. This test is dependent on the air hose operator consistently keeping the air stream on the weld while traveling its length; should the air stream veer off, a leak may be missed. The vacuum box pulls a stronger pressure differential, and is less technique dependant than that of a two-man air hose soap and air test.
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