The role and principle of pre-filter

Why use a pre-filter

Pollution of water pipe network: Local water pipe network is outdated, maintenance and management are ineffective, leakage of pipe network is as high as 20%, and even 40% causes pollution. In 1988, the German government legislation (DIN1988) stipulated that all buildings built after that must install protective impurity filters.

The household pre-cleaning filter is installed at the entrance of the main pipe, and its main function is to intercept the coarse-grained impurities, sediment and rust that cause harm to the household water pipe and water wading equipment in the water, and restore the tap water to the factory state. Avoid damage to the human body and skin; and play a positive role in protecting downstream pipes, water purifiers, water heaters, washing machines, high-end faucets, and flowers, and play a role in scaling solar and water heaters.

why is the filtration precision of the main pre-filters on the market at 100 microns, and a small amount of 50 microns?

During the use of the pre-filter, it often encounters poor water quality and the habit of not regularly discharging sewage, so some impurities embedded in the mesh of the filter element are deeply embedded over time. No matter whether it is siphoning or flushing, it cannot be rinsed clean. User complaints too much. In terms of after-sales service, brushing with toothbrushes and ultrasonic cleaning is also very difficult to maintain, so the products currently launched on the market are all in order to avoid these problems, so the filtration precision of the products is mostly 100 microns, and the filtering effect of such products will definitely be greatly reduced. The results are often unsatisfactory.

The biggest feature of the recoil type pre-filter is: the most thorough sewage. In fact, to truly realize backwashing, it is necessary to design a switch or knob to change the direction of the water flow, so that it is convenient for users to operate.

Types and principles of pre-filters

At present, there are four main types of pre-filters on the market: laminated filter, forward-flushing pre-filter, siphon-type pre-filter, and back-flushing pre-filter.

1. Flushing type pre-filter

Principle: Most of them use 50-100um stainless steel filter screen. The pressure water of tap water penetrates from the inner wall to the outer wall of the pipeline. Impurities such as sediment, rust, red worms, etc. are trapped by the membrane holes. Open the flush valve to replenish the impurities trapped by the stainless steel membrane. The replenishment water is washed away, realizing the flushing of the filter element.
Disadvantages: If the water quality is poor, or the consumer’s habits are not good, the filter element is easy to be blocked. Not only the small impurities cannot be washed out, but they are embedded deeper and tighter in the filter element, which is easy to become secondary pollution. Only open the shell. Take the filter out and scrub with a toothbrush.

2. Laminated filter.

Principle: A large number of micron-sized grooves are engraved on both sides of a thin and specific plastic lamination. When a series of lamination pressures of the same pattern are tightened by springs and liquid pressure on a specially designed inner support, the grooves between the laminations are formed. crossed to form a series of filter elements around 100 microns. During filtration, the water passes through the laminations from the outside, the filter laminations are tightly pressed together under the action of various hydraulic forces of the spring, the impurity particles are trapped at the intersection of the laminations, and the filtered water flows out of the filter. In the backwashing state, when a certain pressure difference or time is reached, the system flushes the controller to control the valve to change the direction of the water flow, so that the impurities on the laminations are flushed out
Disadvantages: Impurities are not washed thoroughly, filtration accuracy is uneven, and there is no sewage outlet.

3. Siphon type pre-filter

Principle: The siphon type pre-filter adopts an external pressure type, which penetrates from the outer wall of the pipe to the inside through the pressure of tap water, and particles such as sediment, rust, and red worms are trapped on the surface by the membrane holes, and the flushing switch is turned on. The water flows around the filter element. Forming a secondary pressure, the built-in water distributor can more effectively remove the dirt and impurities trapped on the filter screen, and the impurities trapped on the membrane surface are washed away by the water through the inner pipe of the rain cutter. Much better in the flushing effect.
Disadvantages: The product structure is complex and the washing is not thorough. For example, the water quality is relatively poor. Some impurities are embedded deeper and tighter in the filter element. Finally, the filter element is blocked, causing secondary pollution. Once blocked, it is very difficult to maintain. Most of the production siphon products filter Accuracy is above 50 microns.

4. Backwash pre-filter

Principle: The backwash pre-filter belongs to the “internal pressure type” under normal working conditions. Through the pressure of tap water, it penetrates from the inner wall of the filter to the outer wall, and particulate impurities such as sediment and rust are trapped in the pipe. The impurities trapped by the filter are washed away by the water. If the water quality is poor and the consumer does not wash it for a long time, there is no need to worry if it is blocked. Through the backwash switch, the piston is moved to the lower part, and the direction of the water flow is changed to “external pressure type”.
Compared with the previous products, the backwashing pre-filter has been greatly improved in technology. The structure is reasonable and the water inlet and outlet can be rotated freely. The installation is convenient, and the water pipe installation in any direction can keep the front body vertical; the flushing design Reasonable “forward flushing and recoiling as you want” to completely flush out impurities and prevent secondary pollution caused by accumulation of impurities. The most critical point is that the accuracy can be as low as 5 microns, which is also not the case with other pre-filters have.

Xi’an CHIWATEC Water Treatment Technology is a high-tech enterprise specialized in various water processing devices. Aside from these individual products, which cover a number of types and series, we can also help with related comprehensive engineering projects. Thanks to our hard work and dedication upon our founding, we are now one of the fastest-developing water treatment equipment manufacturers in Western China.

Further reading:

Portable water pre-treatment system and soft water system (5)

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