• A flow bench is a device that measures the volume or mass of air flowing through a conduit relative to an applied differential pressure. The pressure difference is usually relative to the ambient air pressure (local atmospheric pressure) and is often produced by mechanical means such as a fan or a vacuum motor. The test bench air source circulates air not only through the object being tested but also through the entire test bench. This creates a pressure difference through the tested object and through the primary flow meter element which may be a gate or diaphragm, a Venturi tube or a nozzle.

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• The difference in air pressure is measured at the orifice sides in the test stand. From the pressure difference, it is possible to calculate the volume or mass of air passing through the tested object and even the gas velocity in the geometric cross-section of the tested object.

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• It is often thought that flow benches are only used to test the flow rate of internal combustion engine cylinder heads, but in fact many other components such as carburettors, intake manifolds, exhaust manifolds, turbocharger casings, air filters and nozzles of various types are often found on a flow test bench.