Abstract: A warp knit weft insertion fabric has a plurality of warp yarns and weft insertion yarns of a denier of at least about 1000, each of which yarns is separated from its neighbors by a plurality of yarns of a lower denier of about 220 to about 1800, the ratio of denier of the heavier yarn to lighter yarn being about 1.5 to about 6:1. The arrangement of yarns in both warp and weft is optionally symmetrical, i.e. there are the same number of yarns per inch and the same number and denier of the lighter weight yarns separating the same number and denier of the heavier yarns in both directions. In a particular feature of the invention the yarns in one or both directions are formed in situ by feeding two or more yarns of lower denier in tandem during the knitting process to form a single yarn of higher denier in the finished fabric.The fabric is employed as a reinforcement for sheet material of thermoplastic synthetic resin (by lamination or coating techniques and the like).

Abstract: In a high-speed, high-volume ventilation fan, a noise-attenuating housing structure includes a perforated inner casing contained within a solid-walled outer casing. Filling the space between the inner and outer casings is a porous, sound-absorbing material. To prevent loss of downstream pressure, and therefore operational efficiency, due to leakages of air through the sound-absorbing material from the downstream side at the fan blades to the upstream side thereof, an annular anti-flow barrier is situated in the space between the inner and outer casings slightly downstream of the fan blades. The structure thus provides a high degree of noise attenuation without sacrificing operational efficiency.

Abstract: A sound attenuator comprising concentric inner and outer tubular members having sound absorbing material positioned therebetween. The inner tubular member comprises a lattice of reinforcing strand material coated with solidified resin wherein the strand material is formed in opposed generally helical patterns to provide the lattice. The attenuator is suitable for use in reducing noise produced by axial flow fans used in industrial environs such as mines and factories.

Abstract: A coupling for mine ventilation conduits comprising a first tubular conduit having a flared end portion for receiving an end portion of a second tubular conduit, at least one of the conduits having an elongate flexible strap attached thereto having a length sufficient to reach the other tubular conduit. A resilient compressible strip is placed between said first and second tubular conduits around the periphery of the end position of the second tubular conduit. The coupling also includes a device for tightening the flexible strap length and for holding the strap in a tightened position, the device being secured to one of said conduits and providing for tightening of said strap to draw said tubular conduits together to compress the resilient strip between the flared end portion of the first conduit and the end portion of the second conduit to thereby provide a substantially air tight seal between said conduits.