Air System—A compressed air supply, an exhaust system,
or controllable blower is to be provided to develop the
required air pressure difference across the specimen. The
system shall maintain an essentially constant air pressure
difference for the required test period.
NOTE 3—It is convenient to use a reversible blower or separate pressure
and exhaust systems to provide the required air pressure difference so that
different test specimens can be tested for the effect of positive pressure or
the effect of suction (negative pressure) without reversing the position of
the test specimen. The use of the same specimen for both positive and
negative testing is outside the scope of this test method. If an adequate air
supply is available, a completely airtight seal need not be provided around
the perimeter of the test specimen and the mounting panel, although it is
preferable. However, substantial air leakage will require an air supply of
much greater capacity to maintain the required pressure differences.