introduction

In many industrial and civilian fields today, the requirements for the purity of fluid media are becoming increasingly stringent. Shallow sand filters and self-cleaning filters, as mainstream filtration equipment, each occupy a place with their unique advantages. Accurately understanding their differences in filtration efficiency is crucial for ensuring smooth production processes, improving product quality, and optimizing water resource utilization. A comprehensive comparative analysis will be conducted below.

Overview of Shallow Sand Filters

Review of Structure and Principle

The shallow sand filter mainly consists of a filtering tank, a sand filter layer, a water distribution system, a water collection system, a backwash device, and a control system. The core filtering medium is high-quality quartz sand, which is laid in a multi-layer particle size gradient structure according to the filtering target. During operation, the fluid to be filtered is evenly sprayed onto the sand filter layer through the top water distribution system, and impurities are intercepted and adsorbed between the sand pores. The purified water is collected and discharged by the bottom water collection system. As the filtration progresses, when the pressure difference between the inlet and outlet or the filtration time reaches the set value, the backwash device is activated, and the reverse water flow causes the sand particles to fluidized, stripping impurities to complete self-cleaning, and then restoring the filtration state.

Factors affecting filtration efficiency

Characteristics of sand filter layer: The particle size distribution, particle shape, purity, etc. of quartz sand are directly related to the filtration accuracy and flux. Uniform and appropriately sized sand particles can construct an efficient pore network. If the particle size is too fine, it will cause high water flow resistance and blockage, while if it is too coarse, it will not be able to intercept small impurities.

Uniformity of water distribution and collection: If the water distribution is uneven, the local sand filter layer will be overloaded, affecting the overall filtration effect and filter material life; Uneven water collection can cause local negative pressure, leading to turbulence and the re mixing of filtered impurities into clean water.

Backwash effect: Thorough backwashing is the key to maintaining stable filtration efficiency. The backwash intensity, duration, and cycle need to be precisely controlled, otherwise residual impurities will accumulate and reduce subsequent filtration efficiency.

Overview of self-cleaning filters

Review of Structure and Principle

There are various types of self-cleaning filters, commonly including filter type, filter element type, etc. According to the cleaning method, they can be further divided into suction type, backwash type, etc. The basic structure includes a filtering element (filter screen or filter cartridge), a cleaning mechanism, a drain valve, and a control system. The work is based on pressure difference or timed control. When the inlet and outlet pressure difference reaches the set threshold, it indicates that the filter element is blocked, and the control system triggers the cleaning program. The backwash type uses reverse water flow to impact the filter screen, while the suction type uses negative pressure to remove impurities. The waste generated during cleaning is discharged through the drain valve to ensure the continuous operation of the filter.

Factors affecting filtration efficiency

Filter element accuracy: The pore size of the filter screen or filter element determines the initial filtration accuracy. High precision elements can intercept small particles, but they are prone to clogging and need to be selected according to the appropriate working conditions.

Effectiveness of cleaning methods: Different cleaning methods have varying abilities to remove different impurities. For example, mechanical brush cleaning is effective for removing highly attached impurities, while ultrasonic cleaning is beneficial for removing fine particles and dirt, and should be tailored to local conditions.

Accuracy of control system: Accurate pressure difference, time monitoring and control ensure timely and non excessive cleaning, avoiding filter failure caused by untimely cleaning or damage to filter elements caused by frequent cleaning.

Comparison of filtering accuracy

Shallow sand filter

With a multi-layer sand filter structure, it has good retention ability for impurities in the particle size range of 10-100 microns. In fields such as industrial cooling circulating water and municipal water supply pretreatment, it can effectively remove suspended particles, colloids, algae, etc., ensuring preliminary purification of water quality and meeting the turbidity requirements of general production and life. However, for nanoscale impurities, it is difficult to achieve high-precision filtration solely through sand filtration.

Self cleaning filter

The precision of a self-cleaning filter with a filter screen is usually in the range of tens to hundreds of microns, depending on the filter screen specifications, and is suitable for initial interception of large particle impurities; The filter type can achieve micrometer or even nanometer level precision, such as in electronic chip manufacturing and high-end pharmaceutical processes, which can precisely filter tiny dust, bacteria, viruses, etc., providing protection for ultra clean production. However, the lifespan of high-precision filter elements is greatly affected by impurity concentration.

Comparison of impurity retention ability

Shallow sand filter

The large specific surface area and multi-level pores of the sand filter layer provide sufficient attachment space, and have strong tolerance to sediment, suspended solids and other particulate impurities. Even if the concentration of influent impurities fluctuates greatly, for example, after a storm, the surface water source is used for agricultural irrigation, it can still stably intercept most impurities, and has strong shock load resistance. And it also has a certain adsorption and removal effect on some colloids and microorganisms, with a good comprehensive effect on purifying water quality.

Self cleaning filter

Different types have different targeting, and the filter type is efficient in intercepting larger particles with regular shapes; The filter type has a tight pore structure and strong precision in capturing small and irregular impurities, such as metal particles and impurities in fine chemical raw materials. However, when dealing with sudden changes in impurity concentration, if not cleaned in a timely manner, there is a risk of blockage and a sudden drop in filtration efficiency.

Comparison of filtration stability

Shallow sand filter

A stable physical filtration mechanism combined with reasonable backwash maintenance results in minimal fluctuations in filtration efficiency during long-term operation. As long as the backwash system is regularly inspected to ensure thorough laminar cleaning of the sand filter, it can continuously and stably output standard water quality. It is suitable for industrial production lines that require high water quality stability and continuous operation, such as the cooling circulating water system of large thermal power plants.

Self cleaning filter

The stability is still acceptable during normal operation, but if abnormal situations such as control system failure or cleaning mechanism jamming are not detected and repaired in a timely manner, the filtering effect will rapidly deteriorate. And with the increase of usage time, the high-precision filter element may gradually deteriorate in filtration accuracy even after cleaning, requiring regular replacement of the filter element to maintain stable performance.

Comparison of the impact of maintenance on filtration efficiency

Shallow sand filter

Daily maintenance focuses on inspecting the tank body, valves, and pump body, as well as adjusting backwash parameters, making it easy to operate. Regular backwashing not only does not affect the filtration effect, but also restores the performance of the sand filter layer by removing impurities, ensuring continuous efficiency. Even if the backwash system occasionally malfunctions, the sand filter layer can still maintain a certain filtering capacity in a short period of time, buying time for emergency repairs.

Self cleaning filter

Close attention should be paid to the operation status of the control system and cleaning mechanism. Once a malfunction occurs, it may lead to the accumulation of impurities and damage to the filter elements. If the filter screen is damaged and not detected in a timely manner, it will cause a large amount of unfiltered impurities to mix into the clean water; If the filter element is not replaced in a timely manner, the filtration accuracy will be greatly reduced. The professional requirements for maintenance are relatively high, and improper maintenance has a significant negative impact on the filtering effect.

Comparison of actual application cases

Industrial cooling circulating water system

Using a shallow sand filter, years of operation data have shown that it can stably control suspended particles in circulating water below 50 microns, ensuring the heat exchange efficiency of the condenser, reducing scaling and blockage, and maintaining a stable backwash frequency of 1-2 times per week with low operation and maintenance costs. Although there were seasonal fluctuations in the inflow water quality during this period, it still did not affect the overall filtration effect, ensuring the smooth operation of the production line.

Another similar enterprise uses a filter screen self-cleaning filter, which initially has a good interception effect on large particles. However, during the peak season of algae growth in summer, the filter screen is frequently clogged and the cleaning mechanism is frequently activated, resulting in large pressure fluctuations and unstable filtration accuracy. Some algae fragments penetrate the filter screen, affecting the cooling effect and increasing additional maintenance investment.

High end electronic manufacturing workshop pure water preparation

The self-cleaning filter cartridge filter, with its nanometer level filtration accuracy, strictly removes small impurities from water, ensuring the demand for ultrapure water in chip manufacturing and providing key support for product yield. Although the cost of replacing the filter element is high, it is crucial for production.

If the shallow sand filter is mistakenly used in this scenario, it will not meet the high-precision requirements, and the presence of fine dust and impurities in the water will cause chip short circuits, frequent performance defects, and a surge in production line scrap rates, resulting in huge economic losses.

conclusion

Shallow sand filters and self-cleaning filters each have their own advantages in filtration efficiency. Shallow sand filters are widely used in fields with moderate precision requirements, such as general industrial water, municipal water supply, agricultural irrigation, etc., due to their stability, reliability, strong resistance to impact loads, easy maintenance, and cost-effectiveness; Self cleaning filters, with their high precision and flexible ability to handle complex impurity types, dominate in industries such as electronics, pharmaceuticals, and fine chemicals that require ultra clean production and are sensitive to small impurities. In actual selection, it is necessary to comprehensively consider factors such as water quality characteristics, filtration accuracy requirements, operation and maintenance conditions, cost budget, etc., and accurately match them to achieve the best filtration efficiency and promote the healthy development of various industries.