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Pumps, strainers and filters

A water pump can hardly work without a device to stop solid particles of a certain size (sands, gravel, dead leaves, grass) suspended in water; the suction of these particles may indeed damage the vanes of the volute as well as the inside of the pump body and the valves. (Non-contractual photo, does not necessarily reflect the drawing)

If the water supplied by the pump is intended for sanitary use (shower), it must have a neutral or slightly acid pH (less than 7). If it is used for food, it must also have bacteriological and chemical characteristics defined by the rules of public hygiene.
Facilities providing drinking water to a home must be sampled at least once a year and assigned to a laboratory analysis.
In practice, go to a laboratory, which will supply you with the sample tubes and will take care of it. Municipal authorities are empowered to verify the quality of stand-alone drinking water supply facilities; if they do not meet the standards of hygiene, the mayor may put the user in default to comply with it and, failing that, force him to connect to the water distribution network of the municipality.

The strainer

The first filter, placed upstream of the pump, is constituted by the strainer. It is a part with small holes that prevents the pump from sucking solid bodies larger than the pump tolerates. The diameter of these holes is in fact a compromise between the pressure drop resulting from the presence of the strainer and the need to remove solid particles that could damage the pump. In general, for the strainer of a pump associated with a well, we can be content with holes of fairly large diameter. It is different if the drawing is done in the sandy bed of a river. There are special strainers for suction in a sandy environment, the silica grains of the sand being very corrosive for the pump.
A strainer of this type can be made by combing the original one with a metal sieve (pantry cloth) or a piece of nylon stockings. However, it is necessary to provide that this additional filter will cause a pressure drop, which will affect the maximum capacity of flow and pressure of the pump. It is recommended, when thus strengthening the strainer, to reduce the suction length in a ratio close to that calculated by dividing the diameter of the holes of the original strainer by that of the mesh of the additional sieve.

Suction strainer

Suction strainer


To stop particles as the strainer passes, especially sludge and fine grasses, a filter is inserted between the strainer and the pump inlet. In practice, this filter is directly attached closer to the pump, so as to simplify its accessibility during cleaning. The fast silica filter is most commonly used (especially for feeding pools). It consists of a body of high resistance tank filled to about two thirds of its height, by grains of silica.
A manometer allows to alert the user when the filter is dirty, which results in an increase in pressure beyond a mark. To work properly, this type of filter must let the water pass at a fairly high speed. Depending on the use of the water delivered by the pump, it may be necessary to place another filter downstream of the pump on the discharge port. In this case, it will also take into account the pressure drop thus produced.
This filter can be used to purify water bacteriologically (drinking water) and / or chemical. In particular, for watering from very calcareous water, it is prudent to place a anti-limescale filter and possibly a pH rectifier filter. This last apparatus comprises a tank in which a drip mixes a special product. The flow is adjusted from a calculation table supplied with the product tank, depending on the pH of the pumped water and the one to be reached; pH measurement is easily performed using colorimetric papers sold by pool specialists.

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Video Instruction: Strainer types and Difference between Filter and Strainer in Urdu/Hindi