Conventional downflow sand filters are effective for liquid-solid separation at flow rates up to about 15m3/h.m2 of filter area, although higher rate downflow filters are available. With proper selection of filter media, gelatinous as well as granular suspended matter can be filtered out, without a rapid differential pressure build-up. The bed is cleaned by a […]
The conventional, and still the principal, type of filter used for cleaning bulk water is the sand bed, with backwashing carried out by a backflow of water, or preferably water backwash combined with an air scour. The latter results in better fluidization of the bed and more effective cleansing. Normally, such sand filters are downflow, […]
The main water cycle starts, of course, with rain falling on the earth, most of it making its way to the sea by means of rivers, although the journey may be delayed by lakes. Water derived from the river/lake system is called surface water. The balance of the rain soaks into the ground and becomes […]
After a detailed look at the range of fi ltration equipment, the Handbook now turns to the major applications for the equipment, concentrating on the service or utility applications, but including water fi ltration, which overlaps the boundary between utility and process uses. This and the following section together examine the main liquid fi ltration […]
All of the types of sand filter so far discussed are discontinuous in their operation, even if the cycle is quite long in the case of the slow gravity filter. The most recent development of the rapid sand filter has been to make it continuously operating, by having the bed of sand or other materials […]
The deep-bed filter (often called a sand filter, because that has for long been the filter medium used) is a clarification filter and has been the basic means of treating fresh water to render it safe to drink for over 100 years. The simple gravity sand filter is still its most common form, in terms […]
Electrostatic effects are the cause of two important but opposite phenomena in filtration, especially of gases. In the filtration of dusts from gases, it is possible for electrostatic charges to build up on the filter media. Should these reach a high enough level then a spark discharge could occur, and, if the dust mixture is […]
The attractive force exerted by a magnet on other magnetic materials in its vicinity is at any point proportional to the magnetic field and the magnetic field gradient at that point. A simple way of introducing large field gradients is to use a magnet in a highly sub-divided form, such as an assembly of fine […]
Magnetic separators, so called in the industry, are confusingly exactly the same in principle as a magnetic filter or a magnetic clarifier: attracting and retaining ferro-magnetic solids contained in a product being treated. Particular spheres of application are for the removal of harmful metallic particles and sludges from coolants in re-moulding and machine tool systems, […]
Another important application of the magnetic filter is in the use of a rotating magnetic disc as the filter element, particularly for the treatment of machine tool coolants. The disc unit is designed so that it can be mounted at any height alongside a grinding wheel or honing machine. Coolant from the machine tool is […]
