Filtering of fluid purification process is the means of processing, is mainly used to remove the particulate matter in the fluid or other suspended matter. Filter principle is to use a porous medium, to remove pollutants from fluid (liquid or gas), make the fluid to reach the required level of cleanliness. Filter was often thought of as a simple mesh or sieve, filter or separation was conducted on a surface. This is the way to the past, and now most filters filter has a certain thickness of the wall, that is to say, the filtering equipment has the depth, in the form of "bend channel" has helped to remove pollutants. Filter is to remove a small amount of solid particles in the liquid device, when the fluid is placed into a certain size of filter cartridge, the impurity is blocked, and clean the filtrate by filter outlet, when need to wash, spin spending at the bottom of the pipe plug, net fluid, remove the flange cover, remove the cartridge, after processing to reload. As is known to all, the filter is the core of the original membrane filter, this is a kind of preparation on the microporous layer retainer (support) is full of more small pore membrane. Making membrane filter material has a lot of, is divided into organic membrane (such as polysulfone hollow fiber membrane) and inorganic membrane (such as ceramic membrane). Membrane filter filtration precision is higher, particle size control is stable, and backwash easy recovery performance. Therefore, the use of maintenance is very convenient.

　　1 filtering mechanism and influencing factors

　　1.1 filtering mechanism

　　There are two main types of fluid filtration mechanism. One is based on the size of the particles to separate, such as interception, screening and surface capture; Another is adsorption, namely particle in chemical/charge under the action of adhesion on the filter. This requires each drug company based on their actual needs to choose different membranes.

　　1.2 the factors influencing filtration

　　1.2.1 the characteristics of the fluid

　　Related to the characteristics of the fluid. For example, fluid viscosity and chemical/sub components, the greater the viscosity of fluid in the same stress conditions, the slower the flow velocity, and fluid and have more contact between membrane, filtering effect is better; Such as, the mixing/contact time of fluid and membrane filtering effect also has great influence, mixing and the longer the contact time, the better the filtering effect. In addition, it is important to note that the characteristics of the fluid affects only membrane adsorption intercept effect of fluid without affecting the particle size of exclusion.

　　1.2.2 operating conditions

　　Associated with the actual operating conditions, such as particle velocity and filter pressure. If you want to get good filtering effect, tend to have low velocity, velocity of the low intercept the better the results. Practices prove that the structure of the membrane move is unfavorable for filtering, once the membrane structure has changed, in the process of filtration, particles and fibers from the deep precipitate filter, affect the filtering effect. Speed/pressure difference, however, only have important influence on adsorption intercept, the size effect is fairly small.

　　1.2.3 grain type

　　Particle type and filtering effect also have very big concern, particles are divided into deformable particles and particle two kinds of deformation. Under certain pressure, deformable particles into and lead to more within membranes filter hole blockage, thereby affect the filtering effect, such as gel filtration. However, immutable particle filtering are on the membrane filter to form a layer of the object of similar pie.

　　1. Filter membrane type

　　Related to the type of filtration membrane, the different filtration membrane pore size and structure is different, some of the membrane structure is rigid, some of the membrane structure are mobile. Preliminary rating of the filter membrane pore size is not a unified national standards, different manufacturers have their own definitions and methods, so choosing and replace merchants need high attention, also is a type of the 0.22 mu m membranes, choose different manufacturers filtering effect will there is a big difference. And aseptic filtration public aperture is defined, all merchants to perform the same standard, when choosing and replacement is relatively simple.

　　1.2.5 filter material

　　Associated with the material of filter, filter material according to the relationship with water is divided into hydrophilic (water infiltration) and hydrophobic (water not infiltrate) two kinds. Hydrophilic filter is mainly used in water or water/organic solvent mixture of filtration and aseptic filtration, such as cellulose material (regenerated cellulose, mixed cellulose ester), PVPP polycarbonate modified polyvinylidene fluoride, PVDF; Hydrophobic filter is through the water by intercepting or "boot" into the membrane filter, mainly used in solvents, acid, alkali and chemical filter, tank breathing apparatus/equipment, process gases, fermentation of intake/exhaust filter, such as PTFE teflon, PVDF polyvinylidene fluoride, polypropylene, polysulfone, polycarbonate and so on.

　　2 filter characteristics and structure

　　Filter generally fall into deep filter filter (primary), surface filter filter (middle) and membrane filter filter (depth) 3 kinds. Deep bed filter fiber have fall off, can't give an exact aperture, thickness is in commonly 3 ~ 20 mm, usually with adsorption, and a large carrying capacity; Filter fiber generally with hot glue or membrane surface coating, and can give the rated aperture, thin (< 1 mm), the adsorption capacity is small; The main characteristics of membrane filter is hard, invulnerability to breakage and tortuous channel and very high surface area, there is a certain opening rate, can do integrity testing, often used in deep level filters, such as sterile filter.