What are the different types of well screens?

WELL SCREENS

This article, written by the American Ground Water Trust was originally published in THE AMERICAN WELL OWNER, 2000, Number 3]

WELL SCREENS - WHAT DO THEY DO?

A well screen is an engineered device used in many water wells to help maintain a good water supply from the aquifer and allow for long-term satisfactory operation of the well.

Water wells are constructed in either unconsolidated materials such as sand and gravel or comparatively hard and (usually) stable bedrock. Well screens are installed in wells where the zone containing the water for the well (the aquifer) is comprised of loose or unstable material. The screen prevents rock fragments from entering the well, helps support the wall of the well and allows water to enter. Silt or sand particles may cause excessive abrasion and early failure of the well pump and/ or plugging of equipment in the home. In addition, sand may accumulate in a well and block off water-bearing zones.

In all wells, it is preferable to have water enter slowly. Turbulent flow can more easily transport particles and agitated water may release minerals and clog up the well. Selection of the right screen and the right length of screen can help improve a well’s efficiency and productive life. A commonly used and effective screen type for water wells uses a continuous slot construction, made by wrapping and welding a continuous length of wire or plastic around vertical rods. Wrapped screens have an elongated triangle shape when viewed in cross-section with the “point” of the triangle oriented inwards so that the outside slot width is small compared to the inside spacing. This design allows particles that do penetrate the screen to continue through without getting stuck.

Screens are also made by precision machine slotting (vertical or horizontal slots) or by making louver openings. Louver type well screens (shutter screens) are typically used only for high yield wells. Screens are made in many different slot or opening sizes and are usually installed by fixing the screen to the end of the casing, which is then lowered down the well to the selected water-producing zone(s) of the aquifer.

Many residential wells in bedrock do not need a well screen. Well screens are not a “one size fits all” item, and if one is needed, local well contractors know how to select a screen and choose the appropriate screen length. For most domestic wells a screen length of 4 to 5 feet is usually adequate. State or local well construction codes (in addition to cost) may influence screen selection.

By all means “screen” your wellhead with a flower display or a “wishing well” but don’t pile soil around the well casing and never use pesticides, manure or fertilizers around a water well.

[© American Ground Water Trust. This article may be reprinted for non-commercial educational purposes provided it is used in its entirety and that reference is made to its source as an article in THE AMERICAN WELL OWNER, 2000, Number 3]

Water well screen is a perforated water filter elements. It has a high-efficiency sand control effect, which can well block the formation sand and meet the needs of underground sand control.

Functions of Water Well Screens

In addition to water inflow, it can prevent particles of soil or rock around the well wall from flowing into the well and silting up the well pipe. At the same time, it also supports and protects the well wall, so that the pumping hole can be used normally. For loose pore aquifers or broken bedrock aquifers, suitable Water Well Screens must be installed.

Types of Water well screens

• Mesh type water well screen
  
  If water contains ferrous oxide and calcium carbonate and other salts in the precipitated water, the porosity will be drastically reduced. At the same time, it can be corroded in corrosive water. According to survey data, Mesh well screen rarely have a service life of more than 10 years, and the water production is decreasing year by year.

• Perforated type water well screen
  
  The perforated water well screen is formed by forming a certain geometric shape and a certain regular arrangement of water inlet holes on the well pipe. It can only be used directly in the aquifer above the coarse sand.
  The round slot water well screen is the oldest and simplest type. Generally, metal pipes and asbestos-cement pipes are usually made by drilling or punching. The size of the slots is mainly determined by the grain size of the aquifer. The arrangement of the water inlet holes on the pipe wall usually adopts staggered plum blossoms. 
• Wedge wire water well screen
  The well screen is made of a variety of SS 304 or 316 and other weldable metals, ranging in slot size from 0.2 mm to 4 mm. The screen and housing are manufactured according to customer requirements with threaded or flange connectors. Wedge wire water well screen adopts Vee-shaped wedge wire between the screen gaps. This design form operates more efficiently than other forms of products. Its continuous winding forms a continuous high-density uniform gap on the support rods arranged in a circular manner, which improves the opening area percentage and non-clogging of the screen, and avoids the blockage caused by the high-density accumulation of sediments.

• Bridge slot type water well screens
  
  The bridge-type water well screen has many advantages over other types of water filter pipes due to its special perforation structure. It has the following advantages: the special structure of the bridge slot makes the gravel not easy to block the orifice, and has a high water passing capacity. It has high mechanical strength and is plated with different anti-corrosion coatings according to user needs, which can increase the service life of the well; it can adopt a variety of connection methods, and the operation of the down pipe is convenient; the gap of the bridge hole can be changed to be suitable for different sand and rock geology. The unique spiral structure design greatly increases the tensile strength and compressive strength of the pipe body.

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