An apparatus for determining fluid flow in a pipe includes an ultrasonic flowmeter which communicates with the interior of the pipe through at least one pair of apertures, where each aperture of the one pair of apertures has an effective diameter. The LED itself comprises a p-type semiconductor substrate, a light-generating semiconductor region grown epitaxially thereon, a first electrode on the light-generating semiconductor region, and a second electrode on the underside of the substrate. Consequently, recording processing and the like can be stably performed. A collapsible guard drive is mounted to the hub and includes a pair of collapsible leaves extending from the hub to the tip guard. The means of sealing an interface between the filter media pack and the frame include molding a filter media pack seal, plastic welding outer wraps of filter media pack to the frame, and securing the filter media pack and the frame using a bead of adhesive.