Paint Testing Techniques

PRESSURE DIFFERENTIAL ACROSS PAINT SPRAY BOOTH

A brand new paint spray booth had a control panel in which a Magnehelic differential pressure gauge was installed.  We assumed that the gauge was intended to measure the differential across the dry filters, but upon examination we discovered that only one plastic tube had been attached to one of the two connecting points on the Magnehelic gauge.  The tube was inserted through the sheet metal of the spray booth to the working area where the painter stands.  Why had another tube not been attached to the second connecting point?  It should have been inserted behind the dry filters of the paint spray booth to measure the pressure in the exhaust section.

After giving the problem some thought, we realized that the Magnehelic gauge had been properly installed, but its purpose was to measure the pressure differential across the booth itself.  In this case the purpose was to determine if the volume of air being pushed into the booth by the air makeup system balances the volume of air being pulled out by the exhaust blower. When the differential is either too negative or too positive, one can expect the airflow inside the booth to be turbulent.  Turbulence can cause paint defects, excess orange peel, poor transfer efficiency, etc.

For further details  on how to balance the airflow refer to Ron Joseph’s Environmental Column in Metal Finishing, May 2001.

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