Electroplating filter is using porous filter medium, intercept solid particles in liquid, and solid and liquid separation equipment. In fact in China ancient times already filtering technique is applied to the production, in two hundred BC, has a plant fiber made of paper. In A.D. 105, CAI lun improved the paper making method, he will plant fiber pulp in papermaking process on the density of thin bamboo curtain, bamboo curtain of water gap filtration, a thin layer of wet pulp in bamboo shade on the surface, after dry, the first filtering mostly for gravity filter, then USES the pressurized filter improves the speed, and then again vacuum filter. At the beginning of the 20th century invention of rotary drum vacuum filter realizes the continuous filtering operation. Since then, the various types of filter appeared in succession. Intermittent operation of the filter was developed by can realize automation, filter area is becoming more and more big.

　　Accumulated on the surface of the filter medium in the process of filter cake layer gradually increasing, the liquid through the filter cake layer resistance subsequently heighten, filtration velocity decrease. When filter chamber full of residue or filtering speed is too small, stop filtering, removing residue, the filter medium renewable, in order to achieve a filtration cycle.

　　Liquid through the filter cake layer and filter medium must overcome the resistance, so the electroplating filter must have pressure difference on both sides of the filter medium, this is the driving force to realize filtering. Increase the pressure difference can accelerate the filtering, but after the compression deformation of particles in the large pressure difference filter medium pore blockage, filtering instead of slowing down.

　　Suspending liquid filter has a filter cake layer, deep filtration and screen three ways. Filter cake layer is initiated at the beginning of the filtered, formed the initial filter cake layer, since then, the filter residue layer plays a main role for filtering, then large and small particles are trapped; Deep filtration is refers to the filter medium thick, containing solid particles in suspension is less, and the particles smaller than the channel of the filter medium filtering, after entering particles adsorbed on the pore filtering; Solid particles interception by sieve is filtration is greater than the porosity of the filter medium, the interior of the filter medium is not adsorption solid particle filtering methods, such as rotary drum filter sieve filter the coarse grained impurity in the sewage.

　　In the actual filtering process, three ways are often appear simultaneously or successively. The processing capacity of filter depends on the filtration velocity. Suspension of solid particles, particle size uniform, filter cake layer porosity is relatively smooth, the speed of the filtrate by filter cake layer is bigger. Application of coagulant to set of fine particles into larger clumps, is helpful to improve the filtering speed.

　　Application for suspension solid particle sedimentation speed, feeding on the upper filter medium filter, the filtering direction consistent with the direction of gravity, coarse particle settling first, reduces the filter medium and the filter cake layer congestion; Suspension in difficult to filter (such as colloid) mix, such as kieselguhr, expanded perlite, such as relatively coarse solids, can make the cake layer became loose; When filtrate viscosity is bigger, but heating suspension to reduce viscosity. These measures can speed up the filter.

　　Filter according to acquire the method of filter driver is different, divided into gravity filter, vacuum filter and three types of pressure filtration machine.

　　Gravity filter

　　With the help of the gravity of the suspension and a difference in the pressure of the filter medium is formed on as the filter driver, generally for intermittent operation, such as sand.

　　Vacuum filter

　　Formed in the filtrate outlet pressure as the filter driver. Industrial vacuum filter vacuum absolute pressure for operation (2.5 ~ 8.0) x 105 mpa. When filtering suspension temperature should be lower than the operating vacuum evaporation temperature of the filtrate. This filter is divided into intermittent operation and continuous operation. Intermittent operation of vacuum filter can filter various concentration of suspension. Vacuum leaf filter shell in the container full of suspension. On both sides of the package has a filter cloth filter leaf immersed in suspension, filter leaf inner cavity connected with the vacuum system. Filtrate by catheter after sucked out derivation, the filter residue on the surface of the leaf removal after downtime. Suitable for continuous operation of the vacuum filter filter more thick suspending liquid containing solid particles. Rotary drum vacuum filter, filter surface drum vacuum filter and disk vacuum filter and skip vacuum filter working principle are similar (figure 6). The filtering surface is divided into several separated filter chamber, each rotary filter chamber by distributing valve connected with the fixed tube order, to suck out filter indoor filtrate, lotion, or into the air. Each filter chamber back once complete the whole process of operation, multiple link up the operation of the filter chamber which form a continuous filtration. Belt type vacuum filter structure similar to a belt conveyor, a continuous filter belt, apply to easily filter suspension. Belt type vacuum filter, the filter drum vacuum filter and skip vacuum filter are feeding on the upper filter medium (cloth), especially suitable for large density of solid particles and fast settling slurry.

　　Pressurized filter

　　It takes in suspending liquid inlet pressure or on wet material mechanical squeezing force as filter driver, apply to filter differential pressure demand larger suspension, also divided into intermittent operation and continuous operation. Intermittent operation of shell and tube type pressure filter and pressure leaf filter is used for low concentration slurry filtration. Press filter is a kind of intermittent operation of the pressure filter, is divided into three, plate and frame type, van and vertical use very extensive. Filter oil machine is equipped with oil pump, vacuum evaporator, etc of attachment plate and frame filter press machine. Continuous operation of the drum pressure filter and disc pressure filter in sealed casing pressure filtration, its structure and the rotary drum vacuum filter and disk vacuum filter is similar. Because of its complex structure, less application. Commonly used is the use of pressurized filter chamber volume has shrunk or applying mechanical squeezing force to filter, filter cake moisture content is low, suitable for high solids concentration of suspension. In belt press filter (see belt vacuum filter), after preliminary to take off the liquid gravity or vacuum wet filter cake sandwiched between two filters, then through the roll extrusion to take off the liquid. Screw press filter with porous cylinder, including rotating screw, screw groove depth, material by deep groove end joining into the shallow groove end, filter chamber space gradually decreases, and the material is squeezed, the filtrate by cylinder pore eduction, filter residue discharge by the small end.

　　Precision filter

　　Precision filter is to filter in terms of accuracy, generally between sand filter (filter) and ultrafiltration. Under the action of pressure, raw water through the filter, impurities trapped in the filter wall and the water flows through the filter, so as to achieve the purpose of the filter. At present, the manufacturer of filter equipment scale is given priority to with small and medium-sized enterprises. Product USES the high quality stainless steel, hard polyvinyl chloride (PVC), engineering plastics, organic glass corrosion resistant materials such as shell, which are mainly composed of high quality stainless steel, the built-in filter of different medium. Built-in filter with PE core, honeycomb core, folding core, sintered titanium tube core, activated carbon core and ceramic core, polypropylene fibre filter. Filter filtration effect is different, so the precision filter can according to raw water quality, water quality and water requirements to remove the suspended solids in the water, some of the colloidal material, and fine particulate matter, etc., to achieve different filtration precision. Precision filter filtration precision scope on the market at present is in 0.2 100 um.

　　Water treatment filter

　　Precision filter used as electrodialysis, ion exchange, reverse osmosis and ultrafiltration device used protective filters, can be used in food, pharmaceutical, chemical and electronic industries such as water treatment, such as the food industry: mineral water, fine filtration, beverage, wine clarification filtration treatment. Pharmaceutical industry: sterile water, oral liquid, infusion and injection water treatment; Electronic industry: semiconductor, instrumentation, kinescope factory water preserved, washing water, such as filtering; Chemical industry: organic solvents, esters, alcohols, chemical raw materials such as acid, alkali, oil refining; Environmental protection: electroplating wastewater, printing wastewater, pharmaceutical wastewater, such as all kinds of industrial wastewater treatment. Seawater, brackish water desalination, water treatment, hotel, apartment of feed water treatment, etc.; Courtyard garden, park, greenhouses, livestock, need artificial industrial super fine water mist, and maintenance of high-grade flowers irrigation.