Abstract: A hood structure for air flow measurements on ceiling registers is erected on a fixed square bottom base with an adjustable curtained aperture and mounting for an air flow meter. A hood skirt is stretched by means of four struts that fit against the upper rim to which the skirt is attached (as well as to the base). The rim is made of rigid strips connected together in a ring by securable pivot joints, so that the open top of the hood can have square, round or various elongated shapes for better fitting to a ceiling register or orifice. This enables the use of a smaller bottom frame than would otherwise be necessary for measuring flow out of elongated narrow registers. All but two joints are preferably equipped with pivoted forked braces for securing the angular adjustment of hinged joints connecting angle-bar rim segments by clamping the forked end.

Abstract: Instead of providing a channel in a Pitot tube for measuring static pressure, a channel is provided which terminates in an orifice facing perpendicular to the direction of the flow to be measured, surrounded by a rim having a surface, which may be quite narrow, that is inclined at between 15.degree. and 45.degree., preferably 30.degree., to the plane perpendicular to the axis of the orifice, in order to intensify somewhat the Bernouilli effect of the flow across the orifice. This produces a suction (reduction of pressure) approximately equal to the increase of pressure sensed at an upstream facing orifice of a second channel produced by the same flow which is being measured. A differential manometer connected to the two channels registers about twice the pressure difference that would be measured between the pressure at an upstream facing orifice and the pressure in a channel that measures merely the static pressure in the flowing medium.