Abstract: A method and apparatus for measuring the flow rate of a single phase fluid, particularly a gas, through a conduit. A pulse of tracer fluid is discharged or injected into a first fluid flowing through a conduit, the concentration of the tracer fluid is measured as a function of time at a pont downstream from where it is injected, and the flow rate of the first fluid is determined based on the concentration measurements. The concentration of tracer fluid is preferably sampled substantially continuously from when the tracer gas first passes the measuring point until substantially all of the tracer fluid has passed the measuring point and the sampled concentrations integrated. The concentration of tracer fluid is preferably determined by measuring the thermal conductivity of the mixture of the first fluid and tracer fluid which is dependent upon the concentration of the tracer fluid.

Abstract: A cover is provided for an end of a conduit. The cover comprises a front face covering the conduit end and a back face having fasteners for attachment to a conduit. A plurality of apertures pass between the front face and back face to allow the flow of liquid to and/or from the conduit. The edges of the front face defining the entrances to the apertures are non-planar. In addition to, or as an alternative to, the apertures are formed such that the flow of liquid between the front and back faces is deflected so that the liquid follows at least two directions in passing between the front and back faces. The cover can be used as a grille over drainage in a swimming pool.

Abstract: A cover means (2) is provided for an end of a conduit (9). The cover means comprises a front face (4) covering the conduit end and a back face (6) having attachment means (8) for attachment to the conduit (9). A plurality of apertures (10, 12, 14) pass between the front face (4) and back face (6) to allow the flow of a liquid to and/or from the conduit (9). The edges of the front face defining the entrances to the apertures (10, 12, 14) are non-planar. In addition to, or as an alternative to, the apertures (10, 12, 14) are formed such that the flow of liquid between the front and back faces is deflected so that the liquid follows at least two directions in passing between the front and back faces.