Abstract: A calibration syringe is constructed like a single stage manual pump having a plunger. The input manifold has a duckbill valve that functions to maintain a fixed air flow rate through the syringe even with variable forces acting on the plunger. The duckbill valve has a pair of flexible lips which face upstream against the air flow. As a vacuum is formed inside the pump's input chamber, ambient air pressure closes the flexible lips. Thus, variable plunger forces creates a variable orifice inversely proportional to the plunger force. The result is a constant flow rate syringe.

Abstract: A one piece disposable bacteria/virus filter is suited for all lung tests. The 31/2" outside diameter embodiment has a low 70 cc dead space and a low 0.60 mm H.sub.2 O/liter/second airflow at 12 liters per second. The 4" outside diameter embodiment has a low 70 cc dead space and a low 0.45 cm H.sub.2 O/liter/second airflow at 12 liters per second. Each embodiment has two plastic body halves; each having fins or pins or crosshairs to support the central area of the Filtrete.RTM. internal filter mounted therebetween.