A filter holding device includes an opening portion and a filter. The opening portion communicates between an inside and an outside of the filter holding device. The filter is disposed in the opening portion and includes a first side and a second side. The first side is located adjacent to the inside of the filter holding device. The second side is located adjacent to the outside of the filter holding device. The filter has a larger weight density per unit volume at the second side than a weight density per unit volume at the first side and has a larger area of a surface intersecting a communication direction at the second side than an area of a surface intersecting the communication direction at the first side.

An air filter medium includes a collection layer, an air-permeable adhesive layer, and a porous fluorine resin membrane in this order from upstream to downstream of the filter medium. An initial pressure drop of the filter medium at a permeate flow rate of 5.3 cm/sec is 250 Pa or less. When a test is performed in which polydisperse polyalphaolefin particles having a peak in number in a particle size range of 0.1 to 0.2 μm are allowed to pass through the filter medium at a concentration of 0.2 to 0.5 g/m.sup.3 and a linear velocity of 5.3 cm/sec, the holding amount is 43.0 g/m.sup.2 or more from a moment when the holding amount reaches 20 g/m.sup.2 to when a moment the pressure drop reaches PD.sub.1+120 Pa, where PD.sub.1 is the pressure drop of the filter medium at the moment when the holding amount reaches 20 g/m.sup.2.

Filter media having a gradient in a property and methods associated with such media are provided. In some embodiments, a filter media may have a gradient in mean pore size. The gradient in mean pore size may be across at least a portion of the thickness of the filter media. In some embodiments, the gradient can be represented by an exponential function. The exponential gradient in mean pore size may impart desirable properties to the filter media including enhanced filtration properties (e.g., relatively high dust holding capacity and efficiency), amongst other benefits. The filter media may be particularly well-suited for applications that involve filtering liquids (e.g., hydraulics, fuel, lube, water), though the media may also be used in other applications.

The present invention relates to a filter assembly in which a filter, having a plurality of micropores i.e. openings, which are open in a thickness direction thereof in a state of being extended horizontally or inclinedly with respect to a flow direction of a fluid containing solid foreign substances and have a tapered shape gradually narrowing from upstream ends to downstream ends thereof, is installed communicatively with an upstream end of a branch pipe interposed in a portion of a flow pipe through which the fluid containing the solid foreign substances flows so as to form, in conjunction with the flow pipe, a filtered flow path which passes through the filter and an unfiltered flow path which does not pass through the filter. Therefore, the problem can be solved.

A slip ring system for an electrical machine, comprising: slip rings, which are arranged so as to rotate about an axis of rotation, for transmitting current to the electrical machine; contact brushes which are in contact with the slip rings; an impeller which is mountable so as to surround the axis of rotation and in a rotationally fixed manner in relation to the slip rings, the impeller being adapted to generate an air flow in a plane perpendicular to the shaft; and a filter which surrounds the impeller such that an imaginary radial extension of the impeller meets the filter, and a porosity of the filter decreases in a radially outward direction between a radially inner edge of the filter and a radially outer edge of the filter; wherein a first thickness of the filter in a radial direction is at least 50% of a second thickness of the filter in an axial direction.

The manufacture of fiberglass filtration media, and particularly paint arrestance fiberglass media, is disclosed. Fiberglass filtration media is formed in part by controlling the speed of a melter traversing a drum. The fiberglass media passes through rollers and water sprays before it enters a curing apparatus. Progressive density changes from the air intake side to the air exit side of the media result in increased filtration qualities.

A slip ring system for an electrical machine includes slip rings, which are arranged such that they can rotate about a rotation axis, for transmitting current to the electrical machine; contact brushes which are in contact with the slip rings; and an impeller which can be fitted so as to surround the rotation axis and in a rotationally fixed manner in relation to the slip rings and is adjusted to generate an air flow in a plane perpendicular to the shaft. The impeller has two disc-shaped side walls which surround the shaft and between which a plurality of vanes extend. A filter surrounds the impeller so that an imaginary radial extension of the impeller meets the filter.

A filtering medium includes first and second porous membranes mainly composed of fluororesin, and a plurality of air permeable supports to support the first and second membranes. The second membrane is disposed downstream of the first membrane. When air containing polyalphaolefin particles with a count median diameter of 0.25 ?m is continuously passed through at a flow rate of 5.3 cm/sec and pressure loss is increased by 250 Pa, the first membrane has a dust retention amount larger than the second membrane. The filtering medium has a pressure loss of less than 200 Pa when air is passed through at a flow rate of 5.3 cm/sec. A collecting efficiency of NaCl particles with a particle diameter of 0.3 ?m is 99.97% or more when air containing the NaCl particles is passed through at a flow rate of 5.3 cm/sec. The dust retention amount is 25 g/m.sup.2 or more.

The manufacture of fiberglass filtration media, and particularly paint arrestance fiberglass media, is disclosed. Fiberglass filtration media is formed in part by controlling the speed of a melter traversing a drum. The fiberglass media passes through rollers and water sprays before it enters a curing apparatus. Progressive density changes from the air intake side to the air exit side of the media result in increased filtration qualities.

A filtering medium includes first and second porous membranes mainly composed of fluororesin, and a plurality of air permeable supports to support the first and second membranes. The second membrane is disposed downstream of the first membrane. When air containing polyalphaolefin particles with a count median diameter of 0.25 m is continuously passed through at a flow rate of 5.3 cm/sec and pressure loss is increased by 250 Pa, the first membrane has a dust retention amount larger than the second membrane. The filtering medium has a pressure loss of less than 200 Pa when air is passed through at a flow rate of 5.3 cm/sec. A collecting efficiency of NaCl particles with a particle diameter of 0.3 m is 99.97% or more when air containing the NaCl particles is passed through at a flow rate of 5.3 cm/sec. The dust retention amount is 25 g/m.sup.2 or more.