Rate-of-flow meter, particularly for diagnostic spirometry

A rate-of-flow meter, particularly for diagnostic spirometry, comprising:

• a. wall means defining a flow tube extending along an axis for conducting a gas therethrough;
• b. a measuring stud and a displacement body, each extending radially of said axis through said wall means from the exterior to the interior of said flow tube, said measuring stud and displacement body passing through said wall means at diametrically opposite sides of said flow tube such that the respective ends of said measuring stud and displacement body are in spaced confronting relationship, the space therebetween being substantially less than the interior cross-sectional width of said flow tube and the cross-sectional widths of said measuring stud and displacement body being substantially less than the interior cross-sectional width of said flow tube such that resistance to flow through said flow tube is minimized;
• c. the confronting end of said displacement body terminating in at least one knife edge, and the confronting end of said measuring stud terminating in a longitudinally extending knife edge oriented in a direction substantially perpendicular to said axis;
• d. at least two symmetrically disposed orifices in said measuring stud at opposite sides of said longitudinally extending edge respectively and ducts extending through said measuring stud from said orifices for transmitting the pressure differential on opposite sides of said edge of said measuring studs;
• and
• e. means for displacing one of said displacement body and measuring stud relative to the other in a direction normal to said axis whereby the magnitude of the increase in velocity of flow between said end of said measuring stud and said end of said displacement body can be varied.