Water pre-filter


Preliminary water filters (otherwise called main, coarse water filters or first stage filters) are installed in the inlet line of the home water supply. The body of the primary filtration devices is made of metal or polypropylene materials.

The design is complemented by various types of cleaning elements, the choice of which is determined by the quality of the water and the technical parameters of the water supply.

The device performs mechanical (rough) cleaning without passing harmful suspensions and solid particles of given sizes (rust, sand and other foreign substances).

Purified water is unsuitable for drinking, as it has passed only through the first stage of filtration. However, the installation of first-stage purifiers keeps the plumbing system in proper technical condition and ensures water quality control.

Prefilter device


There are two types of cleaning elements. The first is based on the passage of turbulent water flows through a metal mesh. In the second type of filter, water is purified in a multi-layer cartridge that traps the smallest particles.

In modern filters of the first stage of purification, both varieties are used.

The choice of a specific device is determined by a number of initial physical and technical parameters.

  • Mesh pre-filters. Filtration in them occurs due to the passage of water through a fine-mesh metal mesh. The cell sizes are 50 – 400 micrometers. These cells trap the main types of solids found in tap water. Sand, rust from the pipe walls settle on the filter element. Such devices are known for a long service life without replacing the filter element. The clogged mesh is removed and washed. Then the reverse installation and further operation is possible. A variation of the mesh filter is a direct filter with a magnetic trap. Thanks to a permanent magnet pressed into the cork, it retains iron hydroxides (rust) dissolved in water.
  • Cartridge pre-filters (cartridge) filtration systems. Similar models are fixed on the surface, since the flask takes up a lot of space. Depending on the material of manufacture, its walls transmit or do not transmit light. The transparent design helps to monitor the level of contamination of the flask and cleaning elements. A replaceable cartridge made of filter material (charcoal, pressed fiber, polyester or twisted polypropylene thread) is installed inside. The cleaning ability of the element depends on the material of manufacture, it varies between 20 and 30 microns. Thanks to these characteristics, the initial product (water) is purified from the smallest particles of debris and chlorine (coal cleaning elements). Due to the slow cleaning process, cartridge models should not be installed in high pressure areas. After the expiration of the service life, the cartridge must be disposed of, and a new one is installed in the flask.

The coarse water filter housing consists of a tank (sump) in which water is purified. The tank has two pipes. Through the first comes tap water, and from the second comes purified water.

By body type

  • Pre-filters with a direct arrangement of the housing. In space, they are directed downward, perpendicular to the location of the pipe. They are large in size, so they are installed on those pipes that are located at a distance from the floor and walls.
  • Pre-filters with an oblique arrangement of the housing. Placed at an angle to the inlet pipe. They take up less space than straight lines. Therefore, they are installed on pipes with a small distance to the floor.

Classification of filters by installation method

  • Flanged pre-filters. They are found at interchanges and main pipelines in the basements of residential buildings. Mounted on pipes with an outer diameter of two inches. Installation sites are determined when designing a water supply system. The flanges are fixed and tightened with bolts or studs, making it easy to dismantle the device if necessary.
  • Clutch pre-filters. These filters are installed in apartments. The cleaners are screwed onto pipes with an outer diameter of less than two inches, fixed on a thread or a union nut (commonly called an “American”). This design makes it easy to replace the device even for non-professional plumbers.

The quality of purified water and the performance of the units connected to the water supply system depend on the correct choice of water purifiers. Over time, filtration devices need maintenance. A common cause of filter failure is mud water suspension. Therefore, periodically the meshes or cartridges of water purifiers are replaced or cleaned.

How to clean filter elements

  • Non-flushing pre-filters (mud collectors). This group includes oblique and some straight (vertical installation) cleaners with a removable cover. To remove contamination from the sump of such a device, you need to open the lid and rinse the filter element.
  • Washable pre-filters. On devices of this type, a tap is installed that connects the tank to the sewer. This allows you to drain the sediment and rinse the filter by supplying a direct or reverse flow of water. The project is not difficult to implement if there is a drainage pipe nearby (as an option – draining the washing machine). Despite some technical “nuances”, such solutions are ergonomic, as they do not require manual washing.

How to choose pre-filters


The described coarse cleaning devices can be compared according to the following indicators:

  • Price. Unlike cartridge filter elements, non-flushing metal mesh cleaners are cheaper.
  • Reliability. Where the trouble-free operation of the purifier is critical, the CSF with mesh is preferred. Rare failures of devices are due to violations of the rules of operation or manufacturing defects.
  • Type of shell. In terms of body strength, metal (brass) water purifiers win.
  • Ease of installation. When installing at home, due to their small dimensions, mesh filters with an oblique arrangement of the tank are more convenient. This design does not require additional devices, except for two pipes with cut external threads.
  • Maintenance. The most comfortable in operation are coarse cleaning devices with a mesh element and a straight tank connected to drainage and backwash pipes. The second place in terms of ease of use is in cartridge CSF, in terms of the ease of replacing the cleaning element.
  • filtering ability. Cartridge-type devices filter out even the smallest mechanical impurities. However, they are not used in outdated and worn pipelines with a high concentration of harmful suspensions. These water purifiers are also of little use in wells (own sources of water supply), since the filter elements are clogged with impurities dissolved in water (sand, clay, etc.).
  • According to the execution of the body. Direct sump filters are preferred. They clean large volumes better than devices with an oblique body arrangement.

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The correct choice of filter depends on the characteristics of the water supply.

In order for the purifier to properly perform the functions assigned to it, the terms of reference must adequately describe the initial parameters of the water supply system, the quality and temperature of the water.

  • Attachment type. On pipes with a diameter of two inches, flange fasteners are installed, on pipes with a smaller size – couplings.
  • Possible pollution. In case of heavy pollution, it is worth installing “single-component” filters or combined CSF with several degrees of coarse cleaning, combining mesh elements with replaceable cartridges. If the contamination is not great, it is recommended to install one cartridge cleaner.
  • Water temperature. All types of filters are suitable for cold water supply. For hot water pipes, the equipment is manufactured according to a special technology (preventing damage to the housing and filter element at high temperatures).
  • Free place. The dimensions of the space affect the design of the purifier. If there is enough space, direct filters are installed. For tight areas, it is better to choose oblique water purifiers.
  • Drainage. If the water supply is equipped with a drainage pipe, easy-to-maintain CSFs with backflushing are selected.
  • Stability of pressure in the pipeline. To compensate for pressure drops, it is recommended to install devices with check valves.



CSF are mounted on metal or polypropylene pipes. Water during installation must be blocked by shut-off valves.

Installation rules:

  • It is recommended to install filters before the location of the counters. Since the ingress of mechanical particles into the device can disable it.
  • Filters with oblique reservoirs are installed on horizontal and vertical pipes. At the same time, it is important to take into account the correspondence of the direction of installation of the purifier marked on the body to the direction of water flow.
  • The tank of direct execution is mounted only on horizontal sections of the water supply.
  • CSF with direct flushing should be supplemented with a reverse cleaning system. To do this, a valve is installed that connects the filter input to its output (bypass).

Flange installation
When installing filters with flange fasteners, the factor is taken into account that due to weak tightening, insufficient cleaning or distortion of surfaces, leaks are possible through loose flange connections. Therefore, during the assembly process, it is important to align the fasteners, install seals and correctly tighten the flanges with bolts or studs.

The surfaces to be joined are sealed with a gasket. Mounting holes for bolts (studs) in this case should be located symmetrically to the vertical and horizontal axes, but not coinciding with them.

Bolts are installed and tightened in a checkerboard pattern, heads opposite each other.

Installation of coupling (threaded) connections
Filters are mounted on a site with pre-prepared pipes (threaded). The threaded connection is mounted with an adjustable wrench (open-end or pipe) using a sealant (sanitary flax, polymer thread or paste).

Sealing material is applied to the thread. Then a filter is screwed onto the pipe, and the nuts are tightened with a wrench.



Filter elements contaminated during operation require regular cleaning. Devices that do not provide for automatic flushing are disassembled. The water supply before dismantling is suspended by closing the shut-off valves.

When disassembling, it is recommended to replace the plug seals (on oblique filters they are specially made in the form of a hexagon, for a wrench). The tightness of the connection is improved with sanitary flax.

Dirt accumulated in the oblique filter tank is drained. The filter element (mesh) is cleaned of dirt and blown through with a stream of compressed air. If the filter mesh is damaged, it is replaced with a new one.

CSF with vertical tanks requires unscrewing the flask and draining the precipitate. The filtration element (mesh), as in the previous case, is washed and blown. Old cartridges are replaced with new ones.

If the filter is equipped with a flushing device, for cleaning, periodically open the drain valve of the tank and pass a stream of water through it.

Possible malfunctions

  • Water from the taps flows weakly or does not flow – the filter element is clogged, replace or rinse the cleaning filter.
  • Water is leaking from the filter seals – the tightness of the seal is broken. Replace the seal or winding seal of the threaded connection.

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