The nominal rating of a filter can be expressed by means of this efficiency figure. Given as a percentage, it can be calculated from the beta ratio, or directly from the particle number count: specific to a particular particle size. It applies over the whole particle size range, down to the absolute cut-off value, at […]
The beta ratio is a rating system introduced with the object of giving both filter manufacturer and filter user an accurate and representative comparison among various filter media. It is the ratio between the number of particles per unit volume above a specific size in the suspension upstream of the filter to the same parameter […]
A mean filter rating is a measurement of the mean pore size of a filter element. It is far more meaningful than a nominal filter rating, and, in the case of filter elements with varying pore sizes, more realistic than an absolute rating. It establishes the particle size above which the filter starts to be […]
A nominal rating is an arbitrary value for the performance of a filter, determined by the filter manufacturer, and expressed in terms of percentage retention of a specified contaminant (usually spherical glass beads) of a given size. It also represents a nominal efficiency figure for the filter. Figures typically quoted are at the level of […]
Given that a filter may not be able to remove all of a suspended solid, there will, nevertheless, be a particle size cut-off point above which no particle should be able to pass through the filter. The cut-off point thus refers to the diameter, usually expressed in micrometres (m), of the largest particle that will […]
Filters are rated according to their ability to remove particles of a specific size from a fluid suspension. There are many different methods in which performance may be specified in this way, and quantitative information as to filter performance must always be associated with the corresponding test methods used. The object of a filter is […]
It has been stated that a filter medium is a porous (or at the very least semipermeable) barrier placed across the flow of a suspension to hold back some or all of the suspended material. If this barrier were to be very thin compared with the diameter of the smallest particle to be filtered (and […]
The basis of the particular mechanical separator that is called the filter is the placing across the fluid flow of a barrier, the filter medium. This acts like a porous screen, allowing those arriving particles – which are below a certain size – to pass through the openings that give the medium its porosity, together […]
Contaminants will enter liquid flows from their environment and from any prior treatment or contamination that they have undergone. The prime concern over liquid contamination now and into the foreseeable future is the provision of drinking water free of harmful bacteria and viruses, a provision that is still unavailable to vast areas of the world. […]
As shown in Figure 1.1 , airborne particles may range in size from 1 nm (0.001 um) up to 1 mm or more. The larger particles, such as might come from heavy foundry dust or ground limestone, would need updrafts of the order of 4 or 5m/s to maintain them in suspension. For the very […]
