Room air or outdoor air may be used as the test air source. Relative humidity shall be less than 75%. The exhaust flow may be discharged outdoors, indoors or recirculated. Requirements of certain measuring equipment may impose limits on the temperature of the test air.
Filtration on the exhaust flow is recommended when test aerosol and landing dust may be present.
The test rig consists of several square duct sections with 610mm x 610mm nominal inner dimensions except for the section where the filter is installed. This section has nominal inner dimensions between 616 and 622mm. The length of this duct section shall be at least 1.1 times the length of the filter with a minimum length of 1m.
The duct material shall be electrically conductive and electrically grounded, have smooth interior finish and be sufficiently rigid to maintain its shape at the operating pressure. Smaller parts of the test duct could be made in glass or plastic to see the filter and equipment. Provision of windows to allow monitoring of test progress is desirable.
HEPA filters may be placed upstream of section 1, in which the aerosol for efficiency testing is dispersed and mixed to create a uniform concentration upstream the filter.
Section 2 includes in the upstream section the mixing orifice (10) in the centre of which the dust feeder discharge nozzle is located. Downstream of the dust feeder is a perforated plate (11) intended to achieve a uniform dust distribution. In the last third of this duct is the upstream aerosol sampling head. For assistance test, this sampling head shall be blanked off or removed.