An air velocity gauge for direct measurement of low air flow or draft rates in the range of 20-400 feet per minute comprising a generally flat housing of quadrilateral shape defining a draft way therethrough and a set of opposed draft way inlet and outlet openings that are aligned with the plane of the housing that approximate the size and general shape of the way. A vane formed from a strip of Mylar polyester film is suspended pendulum fashion from the upper portion of the housing adjacent the draft way inlet and is creased longitudinally of same to rigidify the vane to act as such rather than as a flexible flap. The housing itself is in the form of an open centered center frame with open sides, to each side of which is applied a transparent side plate held in place by an adhesively backed opaque scale or scale plate that adheres to lands defined by the housing center frame for this purpose. The scale plates are formed with mirror image windows struck on the arc of movement of the vane that are calibrated to directly read air flow velocity in proportion to the vane deflection about its pivot axis. The housing end plates are formed with cooperating ports for housing a level bubble vial for leveling the gauge; the housing side plates are also formed to define fastener receiving sleeves for mounting the gauge in use.

A velocity measuring instrument of the type having a rotatable, counterweighted, spring-controlled vane and pointer assembly in which the outlet aperture for the fluid is contoured exponentially or logarithmically to present an exit flow area that varies as a function of vane position for linearizing the movement of the vane and pointer assembly in response to the pressure of the fluid on the vane. In one embodiment a true logarithmically varying area port is provided. In other embodiments, two or more openings of varying area or geometry are configured to approximate a logarithmic outlet aperture. A baffle may be provided on the exterior of the case to prevent fluid from entering the outlet aperture, and the interior of the case may be contoured adjacent to the outlet aperture and along the path of the vane to provide a variable leakage path clearance between the vane and the case. A grease-coated surface that contacts the vane and pointer assembly provides viscous damping to prevent pointer oscillation.

An instrument for measuring wind velocity, utilizing impact wind pressure against a movable vane. A spring is used as a mechanical reference and, as such, balances the impact wind force generated against the vane. Flexible means are used to transfer vane motion to a circular indicator disc, which is calibrated in wind speed. Design of kinematic geometry, as well as a unique, non-linear, spring arrangement are employed to counter the square law wind force. Such employment is essential to prevent crowding at the low end of the speed-indicating scale, while maintaining practical full scale values, in a highly sensitive instrument.

A peak flow meter has a flexible resilient vane which is rigidly mounted by one end and which has its other end engaged with a slider indicator which slides in a slot formed in a curved wall of the casing. In use, the human subject blows into the casing through a mouthpiece. The vane is bent by the expiration which vents through the part of the slot between the slider and the mouthpiece. The slider stops at the furthest point from the mouthpiece to which it is moved by the vane and that point is an indication of the peak expiratory flow of the human subject.

An air flow sensing arrangement is disclosed for use in a vacuum cleaner. A plenum chamber or cavity established by a first wall and a second wall is provided adjacent to a fan inlet with all air from a bag chamber being directed radially inward therethrough toward an aperture in the first wall communicating with the fan inlet. The second wall is provided with openings adjacent to its outer periphery so that air is proportionally directed into the cavity along a plurality of paths. An air distribution chamber is established by the second wall and a secondary filter is supported on the second wall. Air is distributed by the distribution chamber about an entire outer surface of a wall portion of the second wall so as to maintan a consistent proportion of air flow through the openings into the cavity in the event irregular filter clogging occurs. A flow sensing device including a pivoting vane having a magnet thereon is disposed within the cavity so as to be within a path of air flowing through the openings. Air impinging against the vane causes it to pivot in an arcuate path to indicate a predetermined air flow level. A switch means is mounted in a position so as to be tangential to arcuate movement of the magnet during a portion of its movement with the switch means being actuated by the magnet when air flow in the cleaner drops to a predetermined low level thereby indicating a condition such as, for example, a full filter bag, low power setting on the cleaner and/or clogged hose.